[1/2] kbuild: remove cc-option test of -fno-stack-protector
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Message ID 20200626185913.92890-1-masahiroy@kernel.org
State New
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  • [1/2] kbuild: remove cc-option test of -fno-stack-protector
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Commit Message

Masahiro Yamada June 26, 2020, 6:59 p.m. UTC
Some Makefiles already pass -fno-stack-protector unconditionally.
For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
No problem report so far about hard-coding this option. So, we can
assume all supported compilers know -fno-stack-protector.

GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)

Get rid of cc-option from -fno-stack-protector.

Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.

Note:
arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
unconditionally, and second conditionally. I removed the second one.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 Documentation/kbuild/kconfig-language.rst | 4 ++--
 Makefile                                  | 2 +-
 arch/Kconfig                              | 3 ---
 arch/arm/boot/compressed/Makefile         | 3 +--
 arch/mips/vdso/Makefile                   | 3 +--
 arch/powerpc/kernel/Makefile              | 2 +-
 arch/powerpc/platforms/powermac/Makefile  | 2 +-
 arch/sparc/vdso/Makefile                  | 4 ++--
 arch/um/Makefile                          | 3 +--
 arch/x86/Makefile                         | 2 +-
 arch/x86/boot/compressed/Makefile         | 2 +-
 arch/x86/entry/vdso/Makefile              | 4 ++--
 arch/x86/kernel/cpu/Makefile              | 3 +--
 arch/x86/lib/Makefile                     | 2 +-
 arch/x86/mm/Makefile                      | 7 +++----
 arch/x86/power/Makefile                   | 3 +--
 arch/x86/purgatory/Makefile               | 2 +-
 arch/x86/um/vdso/Makefile                 | 2 +-
 arch/x86/xen/Makefile                     | 5 ++---
 drivers/firmware/efi/libstub/Makefile     | 2 +-
 drivers/xen/Makefile                      | 3 +--
 kernel/kcsan/Makefile                     | 3 +--
 lib/Makefile                              | 4 ++--
 mm/kasan/Makefile                         | 2 +-
 24 files changed, 30 insertions(+), 42 deletions(-)

Comments

Nick Desaulniers June 26, 2020, 7:09 p.m. UTC | #1
On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Some Makefiles already pass -fno-stack-protector unconditionally.
> For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> No problem report so far about hard-coding this option. So, we can
> assume all supported compilers know -fno-stack-protector.
>
> GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
>
> Get rid of cc-option from -fno-stack-protector.
>
> Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
>
> Note:
> arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> unconditionally, and second conditionally. I removed the second one.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
>  Documentation/kbuild/kconfig-language.rst | 4 ++--
>  Makefile                                  | 2 +-
>  arch/Kconfig                              | 3 ---
>  arch/arm/boot/compressed/Makefile         | 3 +--
>  arch/mips/vdso/Makefile                   | 3 +--
>  arch/powerpc/kernel/Makefile              | 2 +-
>  arch/powerpc/platforms/powermac/Makefile  | 2 +-
>  arch/sparc/vdso/Makefile                  | 4 ++--
>  arch/um/Makefile                          | 3 +--
>  arch/x86/Makefile                         | 2 +-
>  arch/x86/boot/compressed/Makefile         | 2 +-
>  arch/x86/entry/vdso/Makefile              | 4 ++--
>  arch/x86/kernel/cpu/Makefile              | 3 +--
>  arch/x86/lib/Makefile                     | 2 +-
>  arch/x86/mm/Makefile                      | 7 +++----
>  arch/x86/power/Makefile                   | 3 +--
>  arch/x86/purgatory/Makefile               | 2 +-
>  arch/x86/um/vdso/Makefile                 | 2 +-
>  arch/x86/xen/Makefile                     | 5 ++---
>  drivers/firmware/efi/libstub/Makefile     | 2 +-
>  drivers/xen/Makefile                      | 3 +--
>  kernel/kcsan/Makefile                     | 3 +--
>  lib/Makefile                              | 4 ++--
>  mm/kasan/Makefile                         | 2 +-
>  24 files changed, 30 insertions(+), 42 deletions(-)
>
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index a1601ec3317b..2538e7cb08e6 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -540,8 +540,8 @@ followed by a test macro::
>  If you need to expose a compiler capability to makefiles and/or C source files,
>  `CC_HAS_` is the recommended prefix for the config option::
>
> -  config CC_HAS_STACKPROTECTOR_NONE
> -       def_bool $(cc-option,-fno-stack-protector)
> +  config CC_HAS_ASM_GOTO
> +       def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
>
>  Build as module only
>  ~~~~~~~~~~~~~~~~~~~~
> diff --git a/Makefile b/Makefile
> index 5496a32dffa6..73948798ce3f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
>  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
>  endif
>
> -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> +stackp-flags-y                                    := -fno-stack-protector
>  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
>  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8cc35dc556c7..1ea61290900a 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR
>           An arch should select this symbol if:
>           - it has implemented a stack canary (e.g. __stack_chk_guard)
>
> -config CC_HAS_STACKPROTECTOR_NONE
> -       def_bool $(cc-option,-fno-stack-protector)
> -
>  config STACKPROTECTOR
>         bool "Stack Protector buffer overflow detection"
>         depends on HAVE_STACKPROTECTOR
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 00602a6fba04..cb7a56c6723c 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -84,9 +84,8 @@ endif
>
>  # -fstack-protector-strong triggers protection checks in this code,
>  # but it is being used too early to link to meaningful stack_chk logic.
> -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
>  $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
> -       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
> +       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
>
>  # These were previously generated C files. When you are building the kernel
>  # with O=, make sure to remove the stale files in the output tree. Otherwise,
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index 2e64c7600eea..57fe83235281 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \
>         -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
>         -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
>         -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> -       $(call cc-option, -fno-asynchronous-unwind-tables) \
> -       $(call cc-option, -fno-stack-protector)
> +       $(call cc-option, -fno-asynchronous-unwind-tables)
>  aflags-vdso := $(ccflags-vdso) \
>         -D__ASSEMBLY__ -Wa,-gdwarf-2
>
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 244542ae2a91..3a83f2b876a5 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>  CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>  CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>
> -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
> +CFLAGS_prom_init.o += -fno-stack-protector
>  CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
>  CFLAGS_prom_init.o += -ffreestanding
>
> diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> index f4247ade71ca..cf85f0662d0d 100644
> --- a/arch/powerpc/platforms/powermac/Makefile
> +++ b/arch/powerpc/platforms/powermac/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  CFLAGS_bootx_init.o            += -fPIC
> -CFLAGS_bootx_init.o            += $(call cc-option, -fno-stack-protector)
> +CFLAGS_bootx_init.o            += -fno-stack-protector
>
>  KASAN_SANITIZE_bootx_init.o := n
>
> diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> index 708cb6304c2d..f44355e46f31 100644
> --- a/arch/sparc/vdso/Makefile
> +++ b/arch/sparc/vdso/Makefile
> @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>
> @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
> -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS_32 += -fno-stack-protector
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index 3f27aa3ec0a6..1cea46ff9bb7 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
>  LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
>
>  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> -       $(call cc-option, -fno-stack-protector,) \
> -       $(call cc-option, -fno-stack-protector-all,)
> +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)

Just curious, looks like we could do the same for
`-fno-stack-protector-all`, here or tree-wide, right?  Wait, what
compiler recognizes -fno-stack-protector-all?
https://godbolt.org/z/QFQKE_

>
>  # Options used by linker script
>  export LDS_START      := $(START)
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 00e378de8bc0..89c3cdfba753 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -37,7 +37,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
>                    -mno-mmx -mno-sse
>
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
> -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
> +REALMODE_CFLAGS += -fno-stack-protector
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
>  export REALMODE_CFLAGS
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 7619742f91c9..c88a31569a5e 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -36,7 +36,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=small
>  KBUILD_CFLAGS += $(cflags-y)
>  KBUILD_CFLAGS += -mno-mmx -mno-sse
>  KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> -KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> +KBUILD_CFLAGS += -fno-stack-protector
>  KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
>  KBUILD_CFLAGS += -Wno-pointer-sign
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 04e65f0698f6..215376d975a2 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -82,7 +82,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>
> @@ -151,7 +151,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
> -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS_32 += -fno-stack-protector
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> index dba6a83bc349..93792b457b81 100644
> --- a/arch/x86/kernel/cpu/Makefile
> +++ b/arch/x86/kernel/cpu/Makefile
> @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
>  KCSAN_SANITIZE_common.o := n
>
>  # Make sure load_percpu_segment has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_common.o                := $(nostackp)
> +CFLAGS_common.o                := -fno-stack-protector
>
>  obj-y                  := cacheinfo.o scattered.o topology.o
>  obj-y                  += common.o
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index 6110bce7237b..d46fff11f06f 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -24,7 +24,7 @@ ifdef CONFIG_FUNCTION_TRACER
>  CFLAGS_REMOVE_cmdline.o = -pg
>  endif
>
> -CFLAGS_cmdline.o := $(call cc-option, -fno-stack-protector)
> +CFLAGS_cmdline.o := -fno-stack-protector
>  endif
>
>  inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
> diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
> index f7fd0e868c9c..5864219221ca 100644
> --- a/arch/x86/mm/Makefile
> +++ b/arch/x86/mm/Makefile
> @@ -22,10 +22,9 @@ obj-y                                :=  init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
>  obj-y                          += pat/
>
>  # Make sure __phys_addr has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_physaddr.o              := $(nostackp)
> -CFLAGS_setup_nx.o              := $(nostackp)
> -CFLAGS_mem_encrypt_identity.o  := $(nostackp)
> +CFLAGS_physaddr.o              := -fno-stack-protector
> +CFLAGS_setup_nx.o              := -fno-stack-protector
> +CFLAGS_mem_encrypt_identity.o  := -fno-stack-protector
>
>  CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace
>
> diff --git a/arch/x86/power/Makefile b/arch/x86/power/Makefile
> index 37923d715741..6907b523e856 100644
> --- a/arch/x86/power/Makefile
> +++ b/arch/x86/power/Makefile
> @@ -3,8 +3,7 @@ OBJECT_FILES_NON_STANDARD_hibernate_asm_$(BITS).o := y
>
>  # __restore_processor_state() restores %gs after S3 resume and so should not
>  # itself be stack-protected
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_cpu.o   := $(nostackp)
> +CFLAGS_cpu.o   := -fno-stack-protector
>
>  obj-$(CONFIG_PM_SLEEP)         += cpu.o
>  obj-$(CONFIG_HIBERNATION)      += hibernate_$(BITS).o hibernate_asm_$(BITS).o hibernate.o
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 088bd764e0b7..183ac60e5990 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -34,7 +34,7 @@ KCOV_INSTRUMENT := n
>  PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
>  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
>  PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
> -PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
> +PURGATORY_CFLAGS += -fno-stack-protector
>
>  # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
>  # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> index 0caddd6acb22..5943387e3f35 100644
> --- a/arch/x86/um/vdso/Makefile
> +++ b/arch/x86/um/vdso/Makefile
> @@ -42,7 +42,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls
>
>  $(vobjs): KBUILD_CFLAGS += $(CFL)
> diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
> index 084de77a109e..5f1db522d06b 100644
> --- a/arch/x86/xen/Makefile
> +++ b/arch/x86/xen/Makefile
> @@ -9,9 +9,8 @@ CFLAGS_REMOVE_irq.o = -pg
>  endif
>
>  # Make sure early boot has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_enlighten_pv.o          := $(nostackp)
> -CFLAGS_mmu_pv.o                        := $(nostackp)
> +CFLAGS_enlighten_pv.o          := -fno-stack-protector
> +CFLAGS_mmu_pv.o                        := -fno-stack-protector
>
>  obj-y                          += enlighten.o
>  obj-y                          += mmu.o
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 75daaf20374e..f8418763cd79 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -29,7 +29,7 @@ KBUILD_CFLAGS                 := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
>                                    -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
>                                    -D__NO_FORTIFY \
>                                    $(call cc-option,-ffreestanding) \
> -                                  $(call cc-option,-fno-stack-protector) \
> +                                  -fno-stack-protector \
>                                    $(call cc-option,-fno-addrsig) \
>                                    -D__DISABLE_EXPORTS
>
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 0d322f3d90cd..c25c9a699b48 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -5,8 +5,7 @@ obj-y   += mem-reservation.o
>  obj-y  += events/
>  obj-y  += xenbus/
>
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_features.o                      := $(nostackp)
> +CFLAGS_features.o                      := -fno-stack-protector
>
>  dom0-$(CONFIG_ARM64) += arm-device.o
>  dom0-$(CONFIG_PCI) += pci.o
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index d4999b38d1be..d111f32bd5fd 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -7,8 +7,7 @@ CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
>
> -CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
> -       $(call cc-option,-fno-stack-protector,)
> +CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) -fno-stack-protector
>
>  obj-y := core.o debugfs.o report.o
>  obj-$(CONFIG_KCSAN_SELFTEST) += test.o
> diff --git a/lib/Makefile b/lib/Makefile
> index b1c42c10073b..0cda70649f1c 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -22,7 +22,7 @@ KCOV_INSTRUMENT_fault-inject.o := n
>  ifdef CONFIG_AMD_MEM_ENCRYPT
>  KASAN_SANITIZE_string.o := n
>
> -CFLAGS_string.o := $(call cc-option, -fno-stack-protector)
> +CFLAGS_string.o := -fno-stack-protector
>  endif
>
>  # Used by KCSAN while enabled, avoid recursion.
> @@ -300,7 +300,7 @@ endif
>  UBSAN_SANITIZE_ubsan.o := n
>  KASAN_SANITIZE_ubsan.o := n
>  KCSAN_SANITIZE_ubsan.o := n
> -CFLAGS_ubsan.o := $(call cc-option, -fno-stack-protector) $(DISABLE_STACKLEAK_PLUGIN)
> +CFLAGS_ubsan.o := -fno-stack-protector $(DISABLE_STACKLEAK_PLUGIN)
>
>  obj-$(CONFIG_SBITMAP) += sbitmap.o
>
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index d532c2587731..370d970e5ab5 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
>  # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
>  # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
>  CC_FLAGS_KASAN_RUNTIME := $(call cc-option, -fno-conserve-stack)
> -CC_FLAGS_KASAN_RUNTIME += $(call cc-option, -fno-stack-protector)
> +CC_FLAGS_KASAN_RUNTIME += -fno-stack-protector
>  # Disable branch tracing to avoid recursion.
>  CC_FLAGS_KASAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
>
> --
> 2.25.1
>
> --
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Masahiro Yamada June 26, 2020, 8 p.m. UTC | #2
On Sat, Jun 27, 2020 at 4:09 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > Some Makefiles already pass -fno-stack-protector unconditionally.
> > For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> > No problem report so far about hard-coding this option. So, we can
> > assume all supported compilers know -fno-stack-protector.
> >
> > GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
> >
> > Get rid of cc-option from -fno-stack-protector.
> >
> > Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
> >
> > Note:
> > arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> > unconditionally, and second conditionally. I removed the second one.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
> >  Documentation/kbuild/kconfig-language.rst | 4 ++--
> >  Makefile                                  | 2 +-
> >  arch/Kconfig                              | 3 ---
> >  arch/arm/boot/compressed/Makefile         | 3 +--
> >  arch/mips/vdso/Makefile                   | 3 +--
> >  arch/powerpc/kernel/Makefile              | 2 +-
> >  arch/powerpc/platforms/powermac/Makefile  | 2 +-
> >  arch/sparc/vdso/Makefile                  | 4 ++--
> >  arch/um/Makefile                          | 3 +--
> >  arch/x86/Makefile                         | 2 +-
> >  arch/x86/boot/compressed/Makefile         | 2 +-
> >  arch/x86/entry/vdso/Makefile              | 4 ++--
> >  arch/x86/kernel/cpu/Makefile              | 3 +--
> >  arch/x86/lib/Makefile                     | 2 +-
> >  arch/x86/mm/Makefile                      | 7 +++----
> >  arch/x86/power/Makefile                   | 3 +--
> >  arch/x86/purgatory/Makefile               | 2 +-
> >  arch/x86/um/vdso/Makefile                 | 2 +-
> >  arch/x86/xen/Makefile                     | 5 ++---
> >  drivers/firmware/efi/libstub/Makefile     | 2 +-
> >  drivers/xen/Makefile                      | 3 +--
> >  kernel/kcsan/Makefile                     | 3 +--
> >  lib/Makefile                              | 4 ++--
> >  mm/kasan/Makefile                         | 2 +-
> >  24 files changed, 30 insertions(+), 42 deletions(-)
> >
> > diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> > index a1601ec3317b..2538e7cb08e6 100644
> > --- a/Documentation/kbuild/kconfig-language.rst
> > +++ b/Documentation/kbuild/kconfig-language.rst
> > @@ -540,8 +540,8 @@ followed by a test macro::
> >  If you need to expose a compiler capability to makefiles and/or C source files,
> >  `CC_HAS_` is the recommended prefix for the config option::
> >
> > -  config CC_HAS_STACKPROTECTOR_NONE
> > -       def_bool $(cc-option,-fno-stack-protector)
> > +  config CC_HAS_ASM_GOTO
> > +       def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> >
> >  Build as module only
> >  ~~~~~~~~~~~~~~~~~~~~
> > diff --git a/Makefile b/Makefile
> > index 5496a32dffa6..73948798ce3f 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
> >  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
> >  endif
> >
> > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> > +stackp-flags-y                                    := -fno-stack-protector
> >  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
> >  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 8cc35dc556c7..1ea61290900a 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR
> >           An arch should select this symbol if:
> >           - it has implemented a stack canary (e.g. __stack_chk_guard)
> >
> > -config CC_HAS_STACKPROTECTOR_NONE
> > -       def_bool $(cc-option,-fno-stack-protector)
> > -
> >  config STACKPROTECTOR
> >         bool "Stack Protector buffer overflow detection"
> >         depends on HAVE_STACKPROTECTOR
> > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> > index 00602a6fba04..cb7a56c6723c 100644
> > --- a/arch/arm/boot/compressed/Makefile
> > +++ b/arch/arm/boot/compressed/Makefile
> > @@ -84,9 +84,8 @@ endif
> >
> >  # -fstack-protector-strong triggers protection checks in this code,
> >  # but it is being used too early to link to meaningful stack_chk logic.
> > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> >  $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
> > -       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
> > +       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
> >
> >  # These were previously generated C files. When you are building the kernel
> >  # with O=, make sure to remove the stale files in the output tree. Otherwise,
> > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> > index 2e64c7600eea..57fe83235281 100644
> > --- a/arch/mips/vdso/Makefile
> > +++ b/arch/mips/vdso/Makefile
> > @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \
> >         -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
> >         -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
> >         -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> > -       $(call cc-option, -fno-asynchronous-unwind-tables) \
> > -       $(call cc-option, -fno-stack-protector)
> > +       $(call cc-option, -fno-asynchronous-unwind-tables)
> >  aflags-vdso := $(ccflags-vdso) \
> >         -D__ASSEMBLY__ -Wa,-gdwarf-2
> >
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index 244542ae2a91..3a83f2b876a5 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> >  CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> >  CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> >
> > -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
> > +CFLAGS_prom_init.o += -fno-stack-protector
> >  CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
> >  CFLAGS_prom_init.o += -ffreestanding
> >
> > diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> > index f4247ade71ca..cf85f0662d0d 100644
> > --- a/arch/powerpc/platforms/powermac/Makefile
> > +++ b/arch/powerpc/platforms/powermac/Makefile
> > @@ -1,6 +1,6 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  CFLAGS_bootx_init.o            += -fPIC
> > -CFLAGS_bootx_init.o            += $(call cc-option, -fno-stack-protector)
> > +CFLAGS_bootx_init.o            += -fno-stack-protector
> >
> >  KASAN_SANITIZE_bootx_init.o := n
> >
> > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> > index 708cb6304c2d..f44355e46f31 100644
> > --- a/arch/sparc/vdso/Makefile
> > +++ b/arch/sparc/vdso/Makefile
> > @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
> >  # optimize sibling calls.
> >  #
> >  CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> > -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> > +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
> >         -fno-omit-frame-pointer -foptimize-sibling-calls \
> >         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
> >
> > @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
> > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> > +KBUILD_CFLAGS_32 += -fno-stack-protector
> >  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
> >  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
> >  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> > diff --git a/arch/um/Makefile b/arch/um/Makefile
> > index 3f27aa3ec0a6..1cea46ff9bb7 100644
> > --- a/arch/um/Makefile
> > +++ b/arch/um/Makefile
> > @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
> >  LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
> >
> >  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> > -       $(call cc-option, -fno-stack-protector,) \
> > -       $(call cc-option, -fno-stack-protector-all,)
> > +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)
>
> Just curious, looks like we could do the same for
> `-fno-stack-protector-all`, here or tree-wide, right?  Wait, what
> compiler recognizes -fno-stack-protector-all?
> https://godbolt.org/z/QFQKE_


-fstack-protector
-fstack-protector-strong
-fstack-protector-all

are supported.

But,

-fno-stack-protector-strong
-fno-stack-protector-all

are unsupported.



Perheps, -fno-stack-protector is enough
to disable all variants of stack-protector.
Kees Cook June 26, 2020, 8:13 p.m. UTC | #3
On Fri, Jun 26, 2020 at 12:09:37PM -0700, Nick Desaulniers wrote:
> On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> > -       $(call cc-option, -fno-stack-protector,) \
> > -       $(call cc-option, -fno-stack-protector-all,)
> > +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)
> 
> Just curious, looks like we could do the same for
> `-fno-stack-protector-all`, here or tree-wide, right?  Wait, what
> compiler recognizes -fno-stack-protector-all?
> https://godbolt.org/z/QFQKE_

That is from ancient times, IIRC. -fno-stack-protector should be
sufficient.
Nick Desaulniers June 26, 2020, 8:13 p.m. UTC | #4
On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Some Makefiles already pass -fno-stack-protector unconditionally.
> For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> No problem report so far about hard-coding this option. So, we can
> assume all supported compilers know -fno-stack-protector.
>
> GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
>
> Get rid of cc-option from -fno-stack-protector.
>
> Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
>
> Note:
> arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> unconditionally, and second conditionally. I removed the second one.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Generally looks pretty good, just a few more questions before adding
my tag explicitly.

> ---
>
>  Documentation/kbuild/kconfig-language.rst | 4 ++--
>  Makefile                                  | 2 +-
>  arch/Kconfig                              | 3 ---
>  arch/arm/boot/compressed/Makefile         | 3 +--
>  arch/mips/vdso/Makefile                   | 3 +--
>  arch/powerpc/kernel/Makefile              | 2 +-
>  arch/powerpc/platforms/powermac/Makefile  | 2 +-
>  arch/sparc/vdso/Makefile                  | 4 ++--
>  arch/um/Makefile                          | 3 +--
>  arch/x86/Makefile                         | 2 +-
>  arch/x86/boot/compressed/Makefile         | 2 +-
>  arch/x86/entry/vdso/Makefile              | 4 ++--
>  arch/x86/kernel/cpu/Makefile              | 3 +--
>  arch/x86/lib/Makefile                     | 2 +-
>  arch/x86/mm/Makefile                      | 7 +++----
>  arch/x86/power/Makefile                   | 3 +--
>  arch/x86/purgatory/Makefile               | 2 +-
>  arch/x86/um/vdso/Makefile                 | 2 +-
>  arch/x86/xen/Makefile                     | 5 ++---
>  drivers/firmware/efi/libstub/Makefile     | 2 +-
>  drivers/xen/Makefile                      | 3 +--
>  kernel/kcsan/Makefile                     | 3 +--
>  lib/Makefile                              | 4 ++--
>  mm/kasan/Makefile                         | 2 +-
>  24 files changed, 30 insertions(+), 42 deletions(-)
>
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index a1601ec3317b..2538e7cb08e6 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -540,8 +540,8 @@ followed by a test macro::
>  If you need to expose a compiler capability to makefiles and/or C source files,
>  `CC_HAS_` is the recommended prefix for the config option::
>
> -  config CC_HAS_STACKPROTECTOR_NONE
> -       def_bool $(cc-option,-fno-stack-protector)
> +  config CC_HAS_ASM_GOTO
> +       def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
>
>  Build as module only
>  ~~~~~~~~~~~~~~~~~~~~
> diff --git a/Makefile b/Makefile
> index 5496a32dffa6..73948798ce3f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
>  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
>  endif
>
> -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> +stackp-flags-y                                    := -fno-stack-protector
>  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
>  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong

So it looks like the previous behavior always added
`-fno-stack-protector` (since CONFIG_CC_HAS_STACKPROTECTOR_NONE was
always true), but then we append either `-fstack-protector` or
`-fstack-protector-strong` based on configs.  While that's ok, and you
patch doesn't change that behavior, and it's good to be explicit to
set the stack protector or not...it seems weird to have
`-fno-stack-protector -fstack-protector` in the command line flags.  I
would prefer if we checked for not having CONFIG_STACKPROTECTOR or
CONFIG_STACKPROTECTOR_STRONG before adding `-fno-stack-protector`.
That doesn't have to be done in this patch, per se.

>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8cc35dc556c7..1ea61290900a 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR
>           An arch should select this symbol if:
>           - it has implemented a stack canary (e.g. __stack_chk_guard)
>
> -config CC_HAS_STACKPROTECTOR_NONE
> -       def_bool $(cc-option,-fno-stack-protector)
> -
>  config STACKPROTECTOR
>         bool "Stack Protector buffer overflow detection"
>         depends on HAVE_STACKPROTECTOR
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 00602a6fba04..cb7a56c6723c 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -84,9 +84,8 @@ endif
>
>  # -fstack-protector-strong triggers protection checks in this code,
>  # but it is being used too early to link to meaningful stack_chk logic.
> -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
>  $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
> -       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
> +       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
>
>  # These were previously generated C files. When you are building the kernel
>  # with O=, make sure to remove the stale files in the output tree. Otherwise,
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index 2e64c7600eea..57fe83235281 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \
>         -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
>         -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
>         -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> -       $(call cc-option, -fno-asynchronous-unwind-tables) \
> -       $(call cc-option, -fno-stack-protector)
> +       $(call cc-option, -fno-asynchronous-unwind-tables)
>  aflags-vdso := $(ccflags-vdso) \
>         -D__ASSEMBLY__ -Wa,-gdwarf-2
>
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 244542ae2a91..3a83f2b876a5 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>  CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>  CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>
> -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
> +CFLAGS_prom_init.o += -fno-stack-protector
>  CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
>  CFLAGS_prom_init.o += -ffreestanding
>
> diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> index f4247ade71ca..cf85f0662d0d 100644
> --- a/arch/powerpc/platforms/powermac/Makefile
> +++ b/arch/powerpc/platforms/powermac/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  CFLAGS_bootx_init.o            += -fPIC
> -CFLAGS_bootx_init.o            += $(call cc-option, -fno-stack-protector)
> +CFLAGS_bootx_init.o            += -fno-stack-protector
>
>  KASAN_SANITIZE_bootx_init.o := n
>
> diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> index 708cb6304c2d..f44355e46f31 100644
> --- a/arch/sparc/vdso/Makefile
> +++ b/arch/sparc/vdso/Makefile
> @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>
> @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
> -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS_32 += -fno-stack-protector
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index 3f27aa3ec0a6..1cea46ff9bb7 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
>  LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
>
>  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> -       $(call cc-option, -fno-stack-protector,) \
> -       $(call cc-option, -fno-stack-protector-all,)
> +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)
>
>  # Options used by linker script
>  export LDS_START      := $(START)
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 00e378de8bc0..89c3cdfba753 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -37,7 +37,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
>                    -mno-mmx -mno-sse
>
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
> -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
> +REALMODE_CFLAGS += -fno-stack-protector
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
>  export REALMODE_CFLAGS
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 7619742f91c9..c88a31569a5e 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -36,7 +36,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=small
>  KBUILD_CFLAGS += $(cflags-y)
>  KBUILD_CFLAGS += -mno-mmx -mno-sse
>  KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> -KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> +KBUILD_CFLAGS += -fno-stack-protector
>  KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
>  KBUILD_CFLAGS += -Wno-pointer-sign
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 04e65f0698f6..215376d975a2 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -82,7 +82,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>
> @@ -151,7 +151,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
> -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS_32 += -fno-stack-protector
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> index dba6a83bc349..93792b457b81 100644
> --- a/arch/x86/kernel/cpu/Makefile
> +++ b/arch/x86/kernel/cpu/Makefile
> @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
>  KCSAN_SANITIZE_common.o := n
>
>  # Make sure load_percpu_segment has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_common.o                := $(nostackp)
> +CFLAGS_common.o                := -fno-stack-protector

Any time I see `:=` assignment to a CFLAGS variable, it's a red flag
for overwriting existing CFLAGS, which is a common source of bugs.  I
recognize the kernel is current a mix and match for:

CFLAGS_<file>.o

rules to either use `+=` or `:=`, but I wish we were consistent, and
consistent in our use of `+=`.  For those rules, is there a difference
between the use of `+=` and `:=` like there is for the more general
case of appending to KBUILD_CFLAGS?  If not, it's ok to match the
existing style, but it's curious to me in this patch to see a mixed
use of `+=` and `:=`.

>
>  obj-y                  := cacheinfo.o scattered.o topology.o
>  obj-y                  += common.o
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index 6110bce7237b..d46fff11f06f 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -24,7 +24,7 @@ ifdef CONFIG_FUNCTION_TRACER
>  CFLAGS_REMOVE_cmdline.o = -pg
>  endif
>
> -CFLAGS_cmdline.o := $(call cc-option, -fno-stack-protector)
> +CFLAGS_cmdline.o := -fno-stack-protector
>  endif
>
>  inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
> diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
> index f7fd0e868c9c..5864219221ca 100644
> --- a/arch/x86/mm/Makefile
> +++ b/arch/x86/mm/Makefile
> @@ -22,10 +22,9 @@ obj-y                                :=  init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
>  obj-y                          += pat/
>
>  # Make sure __phys_addr has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_physaddr.o              := $(nostackp)
> -CFLAGS_setup_nx.o              := $(nostackp)
> -CFLAGS_mem_encrypt_identity.o  := $(nostackp)
> +CFLAGS_physaddr.o              := -fno-stack-protector
> +CFLAGS_setup_nx.o              := -fno-stack-protector
> +CFLAGS_mem_encrypt_identity.o  := -fno-stack-protector
>
>  CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace
>
> diff --git a/arch/x86/power/Makefile b/arch/x86/power/Makefile
> index 37923d715741..6907b523e856 100644
> --- a/arch/x86/power/Makefile
> +++ b/arch/x86/power/Makefile
> @@ -3,8 +3,7 @@ OBJECT_FILES_NON_STANDARD_hibernate_asm_$(BITS).o := y
>
>  # __restore_processor_state() restores %gs after S3 resume and so should not
>  # itself be stack-protected
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_cpu.o   := $(nostackp)
> +CFLAGS_cpu.o   := -fno-stack-protector
>
>  obj-$(CONFIG_PM_SLEEP)         += cpu.o
>  obj-$(CONFIG_HIBERNATION)      += hibernate_$(BITS).o hibernate_asm_$(BITS).o hibernate.o
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 088bd764e0b7..183ac60e5990 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -34,7 +34,7 @@ KCOV_INSTRUMENT := n
>  PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
>  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
>  PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
> -PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
> +PURGATORY_CFLAGS += -fno-stack-protector
>
>  # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
>  # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> index 0caddd6acb22..5943387e3f35 100644
> --- a/arch/x86/um/vdso/Makefile
> +++ b/arch/x86/um/vdso/Makefile
> @@ -42,7 +42,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls
>
>  $(vobjs): KBUILD_CFLAGS += $(CFL)
> diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
> index 084de77a109e..5f1db522d06b 100644
> --- a/arch/x86/xen/Makefile
> +++ b/arch/x86/xen/Makefile
> @@ -9,9 +9,8 @@ CFLAGS_REMOVE_irq.o = -pg
>  endif
>
>  # Make sure early boot has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_enlighten_pv.o          := $(nostackp)
> -CFLAGS_mmu_pv.o                        := $(nostackp)
> +CFLAGS_enlighten_pv.o          := -fno-stack-protector
> +CFLAGS_mmu_pv.o                        := -fno-stack-protector
>
>  obj-y                          += enlighten.o
>  obj-y                          += mmu.o
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 75daaf20374e..f8418763cd79 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -29,7 +29,7 @@ KBUILD_CFLAGS                 := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
>                                    -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
>                                    -D__NO_FORTIFY \
>                                    $(call cc-option,-ffreestanding) \
> -                                  $(call cc-option,-fno-stack-protector) \
> +                                  -fno-stack-protector \
>                                    $(call cc-option,-fno-addrsig) \
>                                    -D__DISABLE_EXPORTS
>
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 0d322f3d90cd..c25c9a699b48 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -5,8 +5,7 @@ obj-y   += mem-reservation.o
>  obj-y  += events/
>  obj-y  += xenbus/
>
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_features.o                      := $(nostackp)
> +CFLAGS_features.o                      := -fno-stack-protector
>
>  dom0-$(CONFIG_ARM64) += arm-device.o
>  dom0-$(CONFIG_PCI) += pci.o
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index d4999b38d1be..d111f32bd5fd 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -7,8 +7,7 @@ CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
>
> -CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
> -       $(call cc-option,-fno-stack-protector,)
> +CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) -fno-stack-protector
>
>  obj-y := core.o debugfs.o report.o
>  obj-$(CONFIG_KCSAN_SELFTEST) += test.o
> diff --git a/lib/Makefile b/lib/Makefile
> index b1c42c10073b..0cda70649f1c 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -22,7 +22,7 @@ KCOV_INSTRUMENT_fault-inject.o := n
>  ifdef CONFIG_AMD_MEM_ENCRYPT
>  KASAN_SANITIZE_string.o := n
>
> -CFLAGS_string.o := $(call cc-option, -fno-stack-protector)
> +CFLAGS_string.o := -fno-stack-protector
>  endif
>
>  # Used by KCSAN while enabled, avoid recursion.
> @@ -300,7 +300,7 @@ endif
>  UBSAN_SANITIZE_ubsan.o := n
>  KASAN_SANITIZE_ubsan.o := n
>  KCSAN_SANITIZE_ubsan.o := n
> -CFLAGS_ubsan.o := $(call cc-option, -fno-stack-protector) $(DISABLE_STACKLEAK_PLUGIN)
> +CFLAGS_ubsan.o := -fno-stack-protector $(DISABLE_STACKLEAK_PLUGIN)
>
>  obj-$(CONFIG_SBITMAP) += sbitmap.o
>
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index d532c2587731..370d970e5ab5 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
>  # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
>  # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
>  CC_FLAGS_KASAN_RUNTIME := $(call cc-option, -fno-conserve-stack)
> -CC_FLAGS_KASAN_RUNTIME += $(call cc-option, -fno-stack-protector)
> +CC_FLAGS_KASAN_RUNTIME += -fno-stack-protector
>  # Disable branch tracing to avoid recursion.
>  CC_FLAGS_KASAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
>
> --
Kees Cook June 26, 2020, 8:18 p.m. UTC | #5
On Sat, Jun 27, 2020 at 03:59:12AM +0900, Masahiro Yamada wrote:
> Some Makefiles already pass -fno-stack-protector unconditionally.
> For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> No problem report so far about hard-coding this option. So, we can
> assume all supported compilers know -fno-stack-protector.
> 
> GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
> 
> Get rid of cc-option from -fno-stack-protector.
> 
> Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
> 
> Note:
> arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> unconditionally, and second conditionally. I removed the second one.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>
Kees Cook June 26, 2020, 8:21 p.m. UTC | #6
On Fri, Jun 26, 2020 at 01:13:20PM -0700, Nick Desaulniers wrote:
> On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > +++ b/Makefile
> > @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
> >  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
> >  endif
> >
> > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> > +stackp-flags-y                                    := -fno-stack-protector
> >  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
> >  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> 
> So it looks like the previous behavior always added
> `-fno-stack-protector` (since CONFIG_CC_HAS_STACKPROTECTOR_NONE was
> always true), but then we append either `-fstack-protector` or
> `-fstack-protector-strong` based on configs.  While that's ok, and you
> patch doesn't change that behavior, and it's good to be explicit to
> set the stack protector or not...it seems weird to have
> `-fno-stack-protector -fstack-protector` in the command line flags.  I
> would prefer if we checked for not having CONFIG_STACKPROTECTOR or
> CONFIG_STACKPROTECTOR_STRONG before adding `-fno-stack-protector`.
> That doesn't have to be done in this patch, per se.

No, it would add only what was latest and most selected. (They're all
":=" assignments.) If CONFIG_STACKPROTECTOR_STRONG, only
-fstack-protector-strong is set. If only CONFIG_STACKPROTECTOR, only
-fstack-protector is set. Otherwise -fno-stack-protector.
Nick Desaulniers June 26, 2020, 8:25 p.m. UTC | #7
On Fri, Jun 26, 2020 at 1:21 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Jun 26, 2020 at 01:13:20PM -0700, Nick Desaulniers wrote:
> > On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > +++ b/Makefile
> > > @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
> > >  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
> > >  endif
> > >
> > > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> > > +stackp-flags-y                                    := -fno-stack-protector
> > >  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
> > >  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> >
> > So it looks like the previous behavior always added
> > `-fno-stack-protector` (since CONFIG_CC_HAS_STACKPROTECTOR_NONE was
> > always true), but then we append either `-fstack-protector` or
> > `-fstack-protector-strong` based on configs.  While that's ok, and you
> > patch doesn't change that behavior, and it's good to be explicit to
> > set the stack protector or not...it seems weird to have
> > `-fno-stack-protector -fstack-protector` in the command line flags.  I
> > would prefer if we checked for not having CONFIG_STACKPROTECTOR or
> > CONFIG_STACKPROTECTOR_STRONG before adding `-fno-stack-protector`.
> > That doesn't have to be done in this patch, per se.
>
> No, it would add only what was latest and most selected. (They're all
> ":=" assignments.) If CONFIG_STACKPROTECTOR_STRONG, only
> -fstack-protector-strong is set. If only CONFIG_STACKPROTECTOR, only
> -fstack-protector is set. Otherwise -fno-stack-protector.

Ah, right. Thanks for pointing that out.  I'm still curious if the
CFLAGS_<file>.o rules get appended or overwrite all flags for that
translation unit?
Kees Cook June 26, 2020, 8:37 p.m. UTC | #8
On Fri, Jun 26, 2020 at 01:25:27PM -0700, Nick Desaulniers wrote:
> Ah, right. Thanks for pointing that out.  I'm still curious if the
> CFLAGS_<file>.o rules get appended or overwrite all flags for that
> translation unit?

CFLAGS_file.o gets appended to the CFLAGS. For example, after my updated
patch[1], the command line for syscall_64.o looks like this:

gcc -Wp,-MMD,arch/x86/entry/.syscall_64.o.d  -nostdinc -isystem \
...
-Wframe-larger-than=2048 -fstack-protector-strong \
...
-fno-stack-protector -Wno-override-init \
-DKBUILD_MODFILE='"arch/x86/entry/syscall_64"' \
-DKBUILD_BASENAME='"syscall_64"' \
-DKBUILD_MODNAME='"syscall_64"' \
-c -o arch/x86/entry/syscall_64.o \
arch/x86/entry/syscall_64.c

-Kees

[1] https://lore.kernel.org/lkml/202006261333.585319CA6B@keescook/
Ard Biesheuvel June 27, 2020, 7:39 a.m. UTC | #9
On Fri, 26 Jun 2020 at 21:00, Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Some Makefiles already pass -fno-stack-protector unconditionally.
> For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> No problem report so far about hard-coding this option. So, we can
> assume all supported compilers know -fno-stack-protector.
>
> GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
>
> Get rid of cc-option from -fno-stack-protector.
>
> Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
>
> Note:
> arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> unconditionally, and second conditionally. I removed the second one.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>
>  Documentation/kbuild/kconfig-language.rst | 4 ++--
>  Makefile                                  | 2 +-
>  arch/Kconfig                              | 3 ---
>  arch/arm/boot/compressed/Makefile         | 3 +--
>  arch/mips/vdso/Makefile                   | 3 +--
>  arch/powerpc/kernel/Makefile              | 2 +-
>  arch/powerpc/platforms/powermac/Makefile  | 2 +-
>  arch/sparc/vdso/Makefile                  | 4 ++--
>  arch/um/Makefile                          | 3 +--
>  arch/x86/Makefile                         | 2 +-
>  arch/x86/boot/compressed/Makefile         | 2 +-
>  arch/x86/entry/vdso/Makefile              | 4 ++--
>  arch/x86/kernel/cpu/Makefile              | 3 +--
>  arch/x86/lib/Makefile                     | 2 +-
>  arch/x86/mm/Makefile                      | 7 +++----
>  arch/x86/power/Makefile                   | 3 +--
>  arch/x86/purgatory/Makefile               | 2 +-
>  arch/x86/um/vdso/Makefile                 | 2 +-
>  arch/x86/xen/Makefile                     | 5 ++---
>  drivers/firmware/efi/libstub/Makefile     | 2 +-
>  drivers/xen/Makefile                      | 3 +--
>  kernel/kcsan/Makefile                     | 3 +--
>  lib/Makefile                              | 4 ++--
>  mm/kasan/Makefile                         | 2 +-
>  24 files changed, 30 insertions(+), 42 deletions(-)
>
> diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> index a1601ec3317b..2538e7cb08e6 100644
> --- a/Documentation/kbuild/kconfig-language.rst
> +++ b/Documentation/kbuild/kconfig-language.rst
> @@ -540,8 +540,8 @@ followed by a test macro::
>  If you need to expose a compiler capability to makefiles and/or C source files,
>  `CC_HAS_` is the recommended prefix for the config option::
>
> -  config CC_HAS_STACKPROTECTOR_NONE
> -       def_bool $(cc-option,-fno-stack-protector)
> +  config CC_HAS_ASM_GOTO
> +       def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
>
>  Build as module only
>  ~~~~~~~~~~~~~~~~~~~~
> diff --git a/Makefile b/Makefile
> index 5496a32dffa6..73948798ce3f 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
>  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
>  endif
>
> -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> +stackp-flags-y                                    := -fno-stack-protector
>  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
>  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8cc35dc556c7..1ea61290900a 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR
>           An arch should select this symbol if:
>           - it has implemented a stack canary (e.g. __stack_chk_guard)
>
> -config CC_HAS_STACKPROTECTOR_NONE
> -       def_bool $(cc-option,-fno-stack-protector)
> -
>  config STACKPROTECTOR
>         bool "Stack Protector buffer overflow detection"
>         depends on HAVE_STACKPROTECTOR
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index 00602a6fba04..cb7a56c6723c 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -84,9 +84,8 @@ endif
>
>  # -fstack-protector-strong triggers protection checks in this code,
>  # but it is being used too early to link to meaningful stack_chk logic.
> -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
>  $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
> -       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
> +       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
>
>  # These were previously generated C files. When you are building the kernel
>  # with O=, make sure to remove the stale files in the output tree. Otherwise,
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index 2e64c7600eea..57fe83235281 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \
>         -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
>         -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
>         -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> -       $(call cc-option, -fno-asynchronous-unwind-tables) \
> -       $(call cc-option, -fno-stack-protector)
> +       $(call cc-option, -fno-asynchronous-unwind-tables)
>  aflags-vdso := $(ccflags-vdso) \
>         -D__ASSEMBLY__ -Wa,-gdwarf-2
>
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 244542ae2a91..3a83f2b876a5 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>  CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>  CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
>
> -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
> +CFLAGS_prom_init.o += -fno-stack-protector
>  CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
>  CFLAGS_prom_init.o += -ffreestanding
>
> diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> index f4247ade71ca..cf85f0662d0d 100644
> --- a/arch/powerpc/platforms/powermac/Makefile
> +++ b/arch/powerpc/platforms/powermac/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  CFLAGS_bootx_init.o            += -fPIC
> -CFLAGS_bootx_init.o            += $(call cc-option, -fno-stack-protector)
> +CFLAGS_bootx_init.o            += -fno-stack-protector
>
>  KASAN_SANITIZE_bootx_init.o := n
>
> diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> index 708cb6304c2d..f44355e46f31 100644
> --- a/arch/sparc/vdso/Makefile
> +++ b/arch/sparc/vdso/Makefile
> @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>
> @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
> -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS_32 += -fno-stack-protector
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index 3f27aa3ec0a6..1cea46ff9bb7 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
>  LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
>
>  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> -       $(call cc-option, -fno-stack-protector,) \
> -       $(call cc-option, -fno-stack-protector-all,)
> +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)
>
>  # Options used by linker script
>  export LDS_START      := $(START)
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 00e378de8bc0..89c3cdfba753 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -37,7 +37,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
>                    -mno-mmx -mno-sse
>
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
> -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
> +REALMODE_CFLAGS += -fno-stack-protector
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
>  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
>  export REALMODE_CFLAGS
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 7619742f91c9..c88a31569a5e 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -36,7 +36,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=small
>  KBUILD_CFLAGS += $(cflags-y)
>  KBUILD_CFLAGS += -mno-mmx -mno-sse
>  KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> -KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> +KBUILD_CFLAGS += -fno-stack-protector
>  KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
>  KBUILD_CFLAGS += -Wno-pointer-sign
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 04e65f0698f6..215376d975a2 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -82,7 +82,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls \
>         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
>
> @@ -151,7 +151,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
>  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
> -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> +KBUILD_CFLAGS_32 += -fno-stack-protector
>  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
>  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
>  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> index dba6a83bc349..93792b457b81 100644
> --- a/arch/x86/kernel/cpu/Makefile
> +++ b/arch/x86/kernel/cpu/Makefile
> @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
>  KCSAN_SANITIZE_common.o := n
>
>  # Make sure load_percpu_segment has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_common.o                := $(nostackp)
> +CFLAGS_common.o                := -fno-stack-protector
>
>  obj-y                  := cacheinfo.o scattered.o topology.o
>  obj-y                  += common.o
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index 6110bce7237b..d46fff11f06f 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -24,7 +24,7 @@ ifdef CONFIG_FUNCTION_TRACER
>  CFLAGS_REMOVE_cmdline.o = -pg
>  endif
>
> -CFLAGS_cmdline.o := $(call cc-option, -fno-stack-protector)
> +CFLAGS_cmdline.o := -fno-stack-protector
>  endif
>
>  inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
> diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
> index f7fd0e868c9c..5864219221ca 100644
> --- a/arch/x86/mm/Makefile
> +++ b/arch/x86/mm/Makefile
> @@ -22,10 +22,9 @@ obj-y                                :=  init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
>  obj-y                          += pat/
>
>  # Make sure __phys_addr has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_physaddr.o              := $(nostackp)
> -CFLAGS_setup_nx.o              := $(nostackp)
> -CFLAGS_mem_encrypt_identity.o  := $(nostackp)
> +CFLAGS_physaddr.o              := -fno-stack-protector
> +CFLAGS_setup_nx.o              := -fno-stack-protector
> +CFLAGS_mem_encrypt_identity.o  := -fno-stack-protector
>
>  CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace
>
> diff --git a/arch/x86/power/Makefile b/arch/x86/power/Makefile
> index 37923d715741..6907b523e856 100644
> --- a/arch/x86/power/Makefile
> +++ b/arch/x86/power/Makefile
> @@ -3,8 +3,7 @@ OBJECT_FILES_NON_STANDARD_hibernate_asm_$(BITS).o := y
>
>  # __restore_processor_state() restores %gs after S3 resume and so should not
>  # itself be stack-protected
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_cpu.o   := $(nostackp)
> +CFLAGS_cpu.o   := -fno-stack-protector
>
>  obj-$(CONFIG_PM_SLEEP)         += cpu.o
>  obj-$(CONFIG_HIBERNATION)      += hibernate_$(BITS).o hibernate_asm_$(BITS).o hibernate.o
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 088bd764e0b7..183ac60e5990 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -34,7 +34,7 @@ KCOV_INSTRUMENT := n
>  PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
>  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
>  PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
> -PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
> +PURGATORY_CFLAGS += -fno-stack-protector
>
>  # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
>  # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> index 0caddd6acb22..5943387e3f35 100644
> --- a/arch/x86/um/vdso/Makefile
> +++ b/arch/x86/um/vdso/Makefile
> @@ -42,7 +42,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
>  # optimize sibling calls.
>  #
>  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
>         -fno-omit-frame-pointer -foptimize-sibling-calls
>
>  $(vobjs): KBUILD_CFLAGS += $(CFL)
> diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
> index 084de77a109e..5f1db522d06b 100644
> --- a/arch/x86/xen/Makefile
> +++ b/arch/x86/xen/Makefile
> @@ -9,9 +9,8 @@ CFLAGS_REMOVE_irq.o = -pg
>  endif
>
>  # Make sure early boot has no stackprotector
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_enlighten_pv.o          := $(nostackp)
> -CFLAGS_mmu_pv.o                        := $(nostackp)
> +CFLAGS_enlighten_pv.o          := -fno-stack-protector
> +CFLAGS_mmu_pv.o                        := -fno-stack-protector
>
>  obj-y                          += enlighten.o
>  obj-y                          += mmu.o
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 75daaf20374e..f8418763cd79 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -29,7 +29,7 @@ KBUILD_CFLAGS                 := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
>                                    -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
>                                    -D__NO_FORTIFY \
>                                    $(call cc-option,-ffreestanding) \
> -                                  $(call cc-option,-fno-stack-protector) \
> +                                  -fno-stack-protector \
>                                    $(call cc-option,-fno-addrsig) \
>                                    -D__DISABLE_EXPORTS
>
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 0d322f3d90cd..c25c9a699b48 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -5,8 +5,7 @@ obj-y   += mem-reservation.o
>  obj-y  += events/
>  obj-y  += xenbus/
>
> -nostackp := $(call cc-option, -fno-stack-protector)
> -CFLAGS_features.o                      := $(nostackp)
> +CFLAGS_features.o                      := -fno-stack-protector
>
>  dom0-$(CONFIG_ARM64) += arm-device.o
>  dom0-$(CONFIG_PCI) += pci.o
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index d4999b38d1be..d111f32bd5fd 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -7,8 +7,7 @@ CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
>
> -CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
> -       $(call cc-option,-fno-stack-protector,)
> +CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) -fno-stack-protector
>
>  obj-y := core.o debugfs.o report.o
>  obj-$(CONFIG_KCSAN_SELFTEST) += test.o
> diff --git a/lib/Makefile b/lib/Makefile
> index b1c42c10073b..0cda70649f1c 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -22,7 +22,7 @@ KCOV_INSTRUMENT_fault-inject.o := n
>  ifdef CONFIG_AMD_MEM_ENCRYPT
>  KASAN_SANITIZE_string.o := n
>
> -CFLAGS_string.o := $(call cc-option, -fno-stack-protector)
> +CFLAGS_string.o := -fno-stack-protector
>  endif
>
>  # Used by KCSAN while enabled, avoid recursion.
> @@ -300,7 +300,7 @@ endif
>  UBSAN_SANITIZE_ubsan.o := n
>  KASAN_SANITIZE_ubsan.o := n
>  KCSAN_SANITIZE_ubsan.o := n
> -CFLAGS_ubsan.o := $(call cc-option, -fno-stack-protector) $(DISABLE_STACKLEAK_PLUGIN)
> +CFLAGS_ubsan.o := -fno-stack-protector $(DISABLE_STACKLEAK_PLUGIN)
>
>  obj-$(CONFIG_SBITMAP) += sbitmap.o
>
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index d532c2587731..370d970e5ab5 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -16,7 +16,7 @@ CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
>  # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
>  # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
>  CC_FLAGS_KASAN_RUNTIME := $(call cc-option, -fno-conserve-stack)
> -CC_FLAGS_KASAN_RUNTIME += $(call cc-option, -fno-stack-protector)
> +CC_FLAGS_KASAN_RUNTIME += -fno-stack-protector
>  # Disable branch tracing to avoid recursion.
>  CC_FLAGS_KASAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
>
> --
> 2.25.1
>
Masahiro Yamada June 27, 2020, 11:58 a.m. UTC | #10
On Sat, Jun 27, 2020 at 5:13 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > Some Makefiles already pass -fno-stack-protector unconditionally.
> > For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> > No problem report so far about hard-coding this option. So, we can
> > assume all supported compilers know -fno-stack-protector.
> >
> > GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
> >
> > Get rid of cc-option from -fno-stack-protector.
> >
> > Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
> >
> > Note:
> > arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> > unconditionally, and second conditionally. I removed the second one.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
>
> Generally looks pretty good, just a few more questions before adding
> my tag explicitly.
>
> > ---
> >
> >  Documentation/kbuild/kconfig-language.rst | 4 ++--
> >  Makefile                                  | 2 +-
> >  arch/Kconfig                              | 3 ---
> >  arch/arm/boot/compressed/Makefile         | 3 +--
> >  arch/mips/vdso/Makefile                   | 3 +--
> >  arch/powerpc/kernel/Makefile              | 2 +-
> >  arch/powerpc/platforms/powermac/Makefile  | 2 +-
> >  arch/sparc/vdso/Makefile                  | 4 ++--
> >  arch/um/Makefile                          | 3 +--
> >  arch/x86/Makefile                         | 2 +-
> >  arch/x86/boot/compressed/Makefile         | 2 +-
> >  arch/x86/entry/vdso/Makefile              | 4 ++--
> >  arch/x86/kernel/cpu/Makefile              | 3 +--
> >  arch/x86/lib/Makefile                     | 2 +-
> >  arch/x86/mm/Makefile                      | 7 +++----
> >  arch/x86/power/Makefile                   | 3 +--
> >  arch/x86/purgatory/Makefile               | 2 +-
> >  arch/x86/um/vdso/Makefile                 | 2 +-
> >  arch/x86/xen/Makefile                     | 5 ++---
> >  drivers/firmware/efi/libstub/Makefile     | 2 +-
> >  drivers/xen/Makefile                      | 3 +--
> >  kernel/kcsan/Makefile                     | 3 +--
> >  lib/Makefile                              | 4 ++--
> >  mm/kasan/Makefile                         | 2 +-
> >  24 files changed, 30 insertions(+), 42 deletions(-)
> >
> > diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> > index a1601ec3317b..2538e7cb08e6 100644
> > --- a/Documentation/kbuild/kconfig-language.rst
> > +++ b/Documentation/kbuild/kconfig-language.rst
> > @@ -540,8 +540,8 @@ followed by a test macro::
> >  If you need to expose a compiler capability to makefiles and/or C source files,
> >  `CC_HAS_` is the recommended prefix for the config option::
> >
> > -  config CC_HAS_STACKPROTECTOR_NONE
> > -       def_bool $(cc-option,-fno-stack-protector)
> > +  config CC_HAS_ASM_GOTO
> > +       def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> >
> >  Build as module only
> >  ~~~~~~~~~~~~~~~~~~~~
> > diff --git a/Makefile b/Makefile
> > index 5496a32dffa6..73948798ce3f 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
> >  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
> >  endif
> >
> > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> > +stackp-flags-y                                    := -fno-stack-protector
> >  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
> >  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
>
> So it looks like the previous behavior always added
> `-fno-stack-protector` (since CONFIG_CC_HAS_STACKPROTECTOR_NONE was
> always true), but then we append either `-fstack-protector` or
> `-fstack-protector-strong` based on configs.  While that's ok, and you
> patch doesn't change that behavior, and it's good to be explicit to
> set the stack protector or not...it seems weird to have
> `-fno-stack-protector -fstack-protector` in the command line flags.  I
> would prefer if we checked for not having CONFIG_STACKPROTECTOR or
> CONFIG_STACKPROTECTOR_STRONG before adding `-fno-stack-protector`.
> That doesn't have to be done in this patch, per se.
>
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 8cc35dc556c7..1ea61290900a 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR
> >           An arch should select this symbol if:
> >           - it has implemented a stack canary (e.g. __stack_chk_guard)
> >
> > -config CC_HAS_STACKPROTECTOR_NONE
> > -       def_bool $(cc-option,-fno-stack-protector)
> > -
> >  config STACKPROTECTOR
> >         bool "Stack Protector buffer overflow detection"
> >         depends on HAVE_STACKPROTECTOR
> > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> > index 00602a6fba04..cb7a56c6723c 100644
> > --- a/arch/arm/boot/compressed/Makefile
> > +++ b/arch/arm/boot/compressed/Makefile
> > @@ -84,9 +84,8 @@ endif
> >
> >  # -fstack-protector-strong triggers protection checks in this code,
> >  # but it is being used too early to link to meaningful stack_chk logic.
> > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> >  $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
> > -       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
> > +       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
> >
> >  # These were previously generated C files. When you are building the kernel
> >  # with O=, make sure to remove the stale files in the output tree. Otherwise,
> > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> > index 2e64c7600eea..57fe83235281 100644
> > --- a/arch/mips/vdso/Makefile
> > +++ b/arch/mips/vdso/Makefile
> > @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \
> >         -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
> >         -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
> >         -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> > -       $(call cc-option, -fno-asynchronous-unwind-tables) \
> > -       $(call cc-option, -fno-stack-protector)
> > +       $(call cc-option, -fno-asynchronous-unwind-tables)
> >  aflags-vdso := $(ccflags-vdso) \
> >         -D__ASSEMBLY__ -Wa,-gdwarf-2
> >
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index 244542ae2a91..3a83f2b876a5 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> >  CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> >  CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> >
> > -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
> > +CFLAGS_prom_init.o += -fno-stack-protector
> >  CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
> >  CFLAGS_prom_init.o += -ffreestanding
> >
> > diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> > index f4247ade71ca..cf85f0662d0d 100644
> > --- a/arch/powerpc/platforms/powermac/Makefile
> > +++ b/arch/powerpc/platforms/powermac/Makefile
> > @@ -1,6 +1,6 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  CFLAGS_bootx_init.o            += -fPIC
> > -CFLAGS_bootx_init.o            += $(call cc-option, -fno-stack-protector)
> > +CFLAGS_bootx_init.o            += -fno-stack-protector
> >
> >  KASAN_SANITIZE_bootx_init.o := n
> >
> > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> > index 708cb6304c2d..f44355e46f31 100644
> > --- a/arch/sparc/vdso/Makefile
> > +++ b/arch/sparc/vdso/Makefile
> > @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
> >  # optimize sibling calls.
> >  #
> >  CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> > -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> > +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
> >         -fno-omit-frame-pointer -foptimize-sibling-calls \
> >         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
> >
> > @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
> > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> > +KBUILD_CFLAGS_32 += -fno-stack-protector
> >  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
> >  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
> >  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> > diff --git a/arch/um/Makefile b/arch/um/Makefile
> > index 3f27aa3ec0a6..1cea46ff9bb7 100644
> > --- a/arch/um/Makefile
> > +++ b/arch/um/Makefile
> > @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
> >  LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
> >
> >  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> > -       $(call cc-option, -fno-stack-protector,) \
> > -       $(call cc-option, -fno-stack-protector-all,)
> > +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)
> >
> >  # Options used by linker script
> >  export LDS_START      := $(START)
> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > index 00e378de8bc0..89c3cdfba753 100644
> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -37,7 +37,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
> >                    -mno-mmx -mno-sse
> >
> >  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
> > -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
> > +REALMODE_CFLAGS += -fno-stack-protector
> >  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
> >  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
> >  export REALMODE_CFLAGS
> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > index 7619742f91c9..c88a31569a5e 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -36,7 +36,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=small
> >  KBUILD_CFLAGS += $(cflags-y)
> >  KBUILD_CFLAGS += -mno-mmx -mno-sse
> >  KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> > -KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> > +KBUILD_CFLAGS += -fno-stack-protector
> >  KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
> >  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> >  KBUILD_CFLAGS += -Wno-pointer-sign
> > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> > index 04e65f0698f6..215376d975a2 100644
> > --- a/arch/x86/entry/vdso/Makefile
> > +++ b/arch/x86/entry/vdso/Makefile
> > @@ -82,7 +82,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
> >  # optimize sibling calls.
> >  #
> >  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> > -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> > +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
> >         -fno-omit-frame-pointer -foptimize-sibling-calls \
> >         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
> >
> > @@ -151,7 +151,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
> >  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
> > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> > +KBUILD_CFLAGS_32 += -fno-stack-protector
> >  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
> >  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
> >  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> > index dba6a83bc349..93792b457b81 100644
> > --- a/arch/x86/kernel/cpu/Makefile
> > +++ b/arch/x86/kernel/cpu/Makefile
> > @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
> >  KCSAN_SANITIZE_common.o := n
> >
> >  # Make sure load_percpu_segment has no stackprotector
> > -nostackp := $(call cc-option, -fno-stack-protector)
> > -CFLAGS_common.o                := $(nostackp)
> > +CFLAGS_common.o                := -fno-stack-protector
>
> Any time I see `:=` assignment to a CFLAGS variable, it's a red flag
> for overwriting existing CFLAGS, which is a common source of bugs.  I
> recognize the kernel is current a mix and match for:
>
> CFLAGS_<file>.o
>
> rules to either use `+=` or `:=`, but I wish we were consistent, and
> consistent in our use of `+=`.  For those rules, is there a difference
> between the use of `+=` and `:=` like there is for the more general
> case of appending to KBUILD_CFLAGS?  If not, it's ok to match the
> existing style, but it's curious to me in this patch to see a mixed
> use of `+=` and `:=`.


I think Kees mostly answered your question.

Let me add some comments.


'+=' is the most used in kernel Makefiles, but
':=' and '=' are also used.

So, you are right, we are inconsistent.
This applies to not only CFLAGS_<file>.o, but also obj-y, etc.

For example,
https://github.com/torvalds/linux/blob/v5.7/arch/arm64/kernel/Makefile#L15
'obj-y :=' works since it is the first assignment to obj-y in that file.
'obj-y +=' also works, of course.

We can consistently use '+=' everywhere, but I do not send
patches for churn.


You can use any assignment operator to CFLAGS_<file>.o
if it is the first assignment in the Makefile.
Using '+=' is robust for future code insertion/removal, though.


If the right-hand side contains variable references,
there is important difference in the behavior.

You may know two flavors in variables
(https://www.gnu.org/software/make/manual/make.html#Flavors)


CFLAGS_foo.o := $(call cc-option,-fno-stack-protector)
The cc-option is expanded immediately when this line is parsed.
(So, the compiler is invoked for 'make clean' too)


CFLAGS_foo.o += $(call cc-option,-fno-stack-protector)
If this is the first assignment in the file,
'+=' act as '=', so the evaluation of cc-option
is delayed until $(CFLAGS_foo.o) is expanded.
(So, the compiler is NOT invoked for 'make clean')
Nick Desaulniers June 29, 2020, 6:26 p.m. UTC | #11
On Sat, Jun 27, 2020 at 4:59 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sat, Jun 27, 2020 at 5:13 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > Some Makefiles already pass -fno-stack-protector unconditionally.
> > > For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> > > No problem report so far about hard-coding this option. So, we can
> > > assume all supported compilers know -fno-stack-protector.
> > >
> > > GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
> > >
> > > Get rid of cc-option from -fno-stack-protector.
> > >
> > > Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
> > >
> > > Note:
> > > arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> > > unconditionally, and second conditionally. I removed the second one.
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> >
> > Generally looks pretty good, just a few more questions before adding
> > my tag explicitly.
> >
> > > ---
> > >
> > >  Documentation/kbuild/kconfig-language.rst | 4 ++--
> > >  Makefile                                  | 2 +-
> > >  arch/Kconfig                              | 3 ---
> > >  arch/arm/boot/compressed/Makefile         | 3 +--
> > >  arch/mips/vdso/Makefile                   | 3 +--
> > >  arch/powerpc/kernel/Makefile              | 2 +-
> > >  arch/powerpc/platforms/powermac/Makefile  | 2 +-
> > >  arch/sparc/vdso/Makefile                  | 4 ++--
> > >  arch/um/Makefile                          | 3 +--
> > >  arch/x86/Makefile                         | 2 +-
> > >  arch/x86/boot/compressed/Makefile         | 2 +-
> > >  arch/x86/entry/vdso/Makefile              | 4 ++--
> > >  arch/x86/kernel/cpu/Makefile              | 3 +--
> > >  arch/x86/lib/Makefile                     | 2 +-
> > >  arch/x86/mm/Makefile                      | 7 +++----
> > >  arch/x86/power/Makefile                   | 3 +--
> > >  arch/x86/purgatory/Makefile               | 2 +-
> > >  arch/x86/um/vdso/Makefile                 | 2 +-
> > >  arch/x86/xen/Makefile                     | 5 ++---
> > >  drivers/firmware/efi/libstub/Makefile     | 2 +-
> > >  drivers/xen/Makefile                      | 3 +--
> > >  kernel/kcsan/Makefile                     | 3 +--
> > >  lib/Makefile                              | 4 ++--
> > >  mm/kasan/Makefile                         | 2 +-
> > >  24 files changed, 30 insertions(+), 42 deletions(-)
> > >
> > > diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
> > > index a1601ec3317b..2538e7cb08e6 100644
> > > --- a/Documentation/kbuild/kconfig-language.rst
> > > +++ b/Documentation/kbuild/kconfig-language.rst
> > > @@ -540,8 +540,8 @@ followed by a test macro::
> > >  If you need to expose a compiler capability to makefiles and/or C source files,
> > >  `CC_HAS_` is the recommended prefix for the config option::
> > >
> > > -  config CC_HAS_STACKPROTECTOR_NONE
> > > -       def_bool $(cc-option,-fno-stack-protector)
> > > +  config CC_HAS_ASM_GOTO
> > > +       def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
> > >
> > >  Build as module only
> > >  ~~~~~~~~~~~~~~~~~~~~
> > > diff --git a/Makefile b/Makefile
> > > index 5496a32dffa6..73948798ce3f 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0)
> > >  KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
> > >  endif
> > >
> > > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> > > +stackp-flags-y                                    := -fno-stack-protector
> > >  stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
> > >  stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> >
> > So it looks like the previous behavior always added
> > `-fno-stack-protector` (since CONFIG_CC_HAS_STACKPROTECTOR_NONE was
> > always true), but then we append either `-fstack-protector` or
> > `-fstack-protector-strong` based on configs.  While that's ok, and you
> > patch doesn't change that behavior, and it's good to be explicit to
> > set the stack protector or not...it seems weird to have
> > `-fno-stack-protector -fstack-protector` in the command line flags.  I
> > would prefer if we checked for not having CONFIG_STACKPROTECTOR or
> > CONFIG_STACKPROTECTOR_STRONG before adding `-fno-stack-protector`.
> > That doesn't have to be done in this patch, per se.
> >
> > >
> > > diff --git a/arch/Kconfig b/arch/Kconfig
> > > index 8cc35dc556c7..1ea61290900a 100644
> > > --- a/arch/Kconfig
> > > +++ b/arch/Kconfig
> > > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR
> > >           An arch should select this symbol if:
> > >           - it has implemented a stack canary (e.g. __stack_chk_guard)
> > >
> > > -config CC_HAS_STACKPROTECTOR_NONE
> > > -       def_bool $(cc-option,-fno-stack-protector)
> > > -
> > >  config STACKPROTECTOR
> > >         bool "Stack Protector buffer overflow detection"
> > >         depends on HAVE_STACKPROTECTOR
> > > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> > > index 00602a6fba04..cb7a56c6723c 100644
> > > --- a/arch/arm/boot/compressed/Makefile
> > > +++ b/arch/arm/boot/compressed/Makefile
> > > @@ -84,9 +84,8 @@ endif
> > >
> > >  # -fstack-protector-strong triggers protection checks in this code,
> > >  # but it is being used too early to link to meaningful stack_chk logic.
> > > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> > >  $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
> > > -       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
> > > +       $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
> > >
> > >  # These were previously generated C files. When you are building the kernel
> > >  # with O=, make sure to remove the stale files in the output tree. Otherwise,
> > > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> > > index 2e64c7600eea..57fe83235281 100644
> > > --- a/arch/mips/vdso/Makefile
> > > +++ b/arch/mips/vdso/Makefile
> > > @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \
> > >         -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
> > >         -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
> > >         -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> > > -       $(call cc-option, -fno-asynchronous-unwind-tables) \
> > > -       $(call cc-option, -fno-stack-protector)
> > > +       $(call cc-option, -fno-asynchronous-unwind-tables)
> > >  aflags-vdso := $(ccflags-vdso) \
> > >         -D__ASSEMBLY__ -Wa,-gdwarf-2
> > >
> > > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > > index 244542ae2a91..3a83f2b876a5 100644
> > > --- a/arch/powerpc/kernel/Makefile
> > > +++ b/arch/powerpc/kernel/Makefile
> > > @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> > >  CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> > >  CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
> > >
> > > -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
> > > +CFLAGS_prom_init.o += -fno-stack-protector
> > >  CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
> > >  CFLAGS_prom_init.o += -ffreestanding
> > >
> > > diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
> > > index f4247ade71ca..cf85f0662d0d 100644
> > > --- a/arch/powerpc/platforms/powermac/Makefile
> > > +++ b/arch/powerpc/platforms/powermac/Makefile
> > > @@ -1,6 +1,6 @@
> > >  # SPDX-License-Identifier: GPL-2.0
> > >  CFLAGS_bootx_init.o            += -fPIC
> > > -CFLAGS_bootx_init.o            += $(call cc-option, -fno-stack-protector)
> > > +CFLAGS_bootx_init.o            += -fno-stack-protector
> > >
> > >  KASAN_SANITIZE_bootx_init.o := n
> > >
> > > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> > > index 708cb6304c2d..f44355e46f31 100644
> > > --- a/arch/sparc/vdso/Makefile
> > > +++ b/arch/sparc/vdso/Makefile
> > > @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
> > >  # optimize sibling calls.
> > >  #
> > >  CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> > > -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> > > +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
> > >         -fno-omit-frame-pointer -foptimize-sibling-calls \
> > >         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
> > >
> > > @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
> > >  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
> > >  KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
> > >  KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
> > > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> > > +KBUILD_CFLAGS_32 += -fno-stack-protector
> > >  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
> > >  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
> > >  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> > > diff --git a/arch/um/Makefile b/arch/um/Makefile
> > > index 3f27aa3ec0a6..1cea46ff9bb7 100644
> > > --- a/arch/um/Makefile
> > > +++ b/arch/um/Makefile
> > > @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
> > >  LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
> > >
> > >  CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
> > > -       $(call cc-option, -fno-stack-protector,) \
> > > -       $(call cc-option, -fno-stack-protector-all,)
> > > +       -fno-stack-protector $(call cc-option, -fno-stack-protector-all)
> > >
> > >  # Options used by linker script
> > >  export LDS_START      := $(START)
> > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > > index 00e378de8bc0..89c3cdfba753 100644
> > > --- a/arch/x86/Makefile
> > > +++ b/arch/x86/Makefile
> > > @@ -37,7 +37,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
> > >                    -mno-mmx -mno-sse
> > >
> > >  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
> > > -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
> > > +REALMODE_CFLAGS += -fno-stack-protector
> > >  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
> > >  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
> > >  export REALMODE_CFLAGS
> > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > > index 7619742f91c9..c88a31569a5e 100644
> > > --- a/arch/x86/boot/compressed/Makefile
> > > +++ b/arch/x86/boot/compressed/Makefile
> > > @@ -36,7 +36,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=small
> > >  KBUILD_CFLAGS += $(cflags-y)
> > >  KBUILD_CFLAGS += -mno-mmx -mno-sse
> > >  KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> > > -KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> > > +KBUILD_CFLAGS += -fno-stack-protector
> > >  KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
> > >  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> > >  KBUILD_CFLAGS += -Wno-pointer-sign
> > > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> > > index 04e65f0698f6..215376d975a2 100644
> > > --- a/arch/x86/entry/vdso/Makefile
> > > +++ b/arch/x86/entry/vdso/Makefile
> > > @@ -82,7 +82,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
> > >  # optimize sibling calls.
> > >  #
> > >  CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
> > > -       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
> > > +       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
> > >         -fno-omit-frame-pointer -foptimize-sibling-calls \
> > >         -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
> > >
> > > @@ -151,7 +151,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
> > >  KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
> > >  KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
> > >  KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
> > > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
> > > +KBUILD_CFLAGS_32 += -fno-stack-protector
> > >  KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
> > >  KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
> > >  KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
> > > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> > > index dba6a83bc349..93792b457b81 100644
> > > --- a/arch/x86/kernel/cpu/Makefile
> > > +++ b/arch/x86/kernel/cpu/Makefile
> > > @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
> > >  KCSAN_SANITIZE_common.o := n
> > >
> > >  # Make sure load_percpu_segment has no stackprotector
> > > -nostackp := $(call cc-option, -fno-stack-protector)
> > > -CFLAGS_common.o                := $(nostackp)
> > > +CFLAGS_common.o                := -fno-stack-protector
> >
> > Any time I see `:=` assignment to a CFLAGS variable, it's a red flag
> > for overwriting existing CFLAGS, which is a common source of bugs.  I
> > recognize the kernel is current a mix and match for:
> >
> > CFLAGS_<file>.o
> >
> > rules to either use `+=` or `:=`, but I wish we were consistent, and
> > consistent in our use of `+=`.  For those rules, is there a difference
> > between the use of `+=` and `:=` like there is for the more general
> > case of appending to KBUILD_CFLAGS?  If not, it's ok to match the
> > existing style, but it's curious to me in this patch to see a mixed
> > use of `+=` and `:=`.
>
>
> I think Kees mostly answered your question.
>
> Let me add some comments.
>
>
> '+=' is the most used in kernel Makefiles, but
> ':=' and '=' are also used.
>
> So, you are right, we are inconsistent.
> This applies to not only CFLAGS_<file>.o, but also obj-y, etc.
>
> For example,
> https://github.com/torvalds/linux/blob/v5.7/arch/arm64/kernel/Makefile#L15
> 'obj-y :=' works since it is the first assignment to obj-y in that file.
> 'obj-y +=' also works, of course.
>
> We can consistently use '+=' everywhere, but I do not send
> patches for churn.
>
>
> You can use any assignment operator to CFLAGS_<file>.o
> if it is the first assignment in the Makefile.
> Using '+=' is robust for future code insertion/removal, though.
>
>
> If the right-hand side contains variable references,
> there is important difference in the behavior.
>
> You may know two flavors in variables
> (https://www.gnu.org/software/make/manual/make.html#Flavors)

Cool, thanks for all the info.  With that, I'm happy with this patch.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>


> CFLAGS_foo.o := $(call cc-option,-fno-stack-protector)
> The cc-option is expanded immediately when this line is parsed.
> (So, the compiler is invoked for 'make clean' too)
>
>
> CFLAGS_foo.o += $(call cc-option,-fno-stack-protector)
> If this is the first assignment in the file,
> '+=' act as '=', so the evaluation of cc-option
> is delayed until $(CFLAGS_foo.o) is expanded.
> (So, the compiler is NOT invoked for 'make clean')

Ah, I think that may explain: I've been seeing the occasional warning
from $(NM) when running `make clean` for ARCH=arm, I'll bet that's
where this is coming from then.  Next time I reproduce it, I'll try to
find maybe where we're using `:=` or `=` with `$(NM)`.

Maybe arch/arm/boot/compressed/Makefile, KBSS_SZ is evaluated for
`make clean`? (If you start an arm build, but kill it before vmlinux
is created, then `make clean` I suspect that KBSS_SZ is evaluated?)
Nick Desaulniers June 29, 2020, 10:39 p.m. UTC | #12
On Mon, Jun 29, 2020 at 11:26 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Sat, Jun 27, 2020 at 4:59 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Sat, Jun 27, 2020 at 5:13 AM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > >
> > > > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> > > > index dba6a83bc349..93792b457b81 100644
> > > > --- a/arch/x86/kernel/cpu/Makefile
> > > > +++ b/arch/x86/kernel/cpu/Makefile
> > > > @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
> > > >  KCSAN_SANITIZE_common.o := n
> > > >
> > > >  # Make sure load_percpu_segment has no stackprotector
> > > > -nostackp := $(call cc-option, -fno-stack-protector)
> > > > -CFLAGS_common.o                := $(nostackp)
> > > > +CFLAGS_common.o                := -fno-stack-protector
> > >
> > > Any time I see `:=` assignment to a CFLAGS variable, it's a red flag
> > > for overwriting existing CFLAGS, which is a common source of bugs.  I
> > > recognize the kernel is current a mix and match for:
> > >
> > > CFLAGS_<file>.o
> > >
> > > rules to either use `+=` or `:=`, but I wish we were consistent, and
> > > consistent in our use of `+=`.  For those rules, is there a difference
> > > between the use of `+=` and `:=` like there is for the more general
> > > case of appending to KBUILD_CFLAGS?  If not, it's ok to match the
> > > existing style, but it's curious to me in this patch to see a mixed
> > > use of `+=` and `:=`.
> >
> >
> > I think Kees mostly answered your question.
> >
> > Let me add some comments.
> >
> >
> > '+=' is the most used in kernel Makefiles, but
> > ':=' and '=' are also used.
> >
> > So, you are right, we are inconsistent.
> > This applies to not only CFLAGS_<file>.o, but also obj-y, etc.
> >
> > For example,
> > https://github.com/torvalds/linux/blob/v5.7/arch/arm64/kernel/Makefile#L15
> > 'obj-y :=' works since it is the first assignment to obj-y in that file.
> > 'obj-y +=' also works, of course.
> >
> > We can consistently use '+=' everywhere, but I do not send
> > patches for churn.
> >
> >
> > You can use any assignment operator to CFLAGS_<file>.o
> > if it is the first assignment in the Makefile.
> > Using '+=' is robust for future code insertion/removal, though.
> >
> >
> > If the right-hand side contains variable references,
> > there is important difference in the behavior.
> >
> > You may know two flavors in variables
> > (https://www.gnu.org/software/make/manual/make.html#Flavors)
>
> Cool, thanks for all the info.  With that, I'm happy with this patch.
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
>
> > CFLAGS_foo.o := $(call cc-option,-fno-stack-protector)
> > The cc-option is expanded immediately when this line is parsed.
> > (So, the compiler is invoked for 'make clean' too)
> >
> >
> > CFLAGS_foo.o += $(call cc-option,-fno-stack-protector)
> > If this is the first assignment in the file,
> > '+=' act as '=', so the evaluation of cc-option
> > is delayed until $(CFLAGS_foo.o) is expanded.
> > (So, the compiler is NOT invoked for 'make clean')
>
> Ah, I think that may explain: I've been seeing the occasional warning
> from $(NM) when running `make clean` for ARCH=arm, I'll bet that's
> where this is coming from then.  Next time I reproduce it, I'll try to
> find maybe where we're using `:=` or `=` with `$(NM)`.
>
> Maybe arch/arm/boot/compressed/Makefile, KBSS_SZ is evaluated for
> `make clean`? (If you start an arm build, but kill it before vmlinux
> is created, then `make clean` I suspect that KBSS_SZ is evaluated?)

$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 -j71
$ rm vmlinux
$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 -j71 clean
llvm-nm: error: arch/arm/boot/compressed/../../../../vmlinux: No such
file or directory.

I suspect I see this from doing an ARCH=arm build, then building a
different ARCH and killing the build before vmlinux is produced or
`make clean` for a different ARCH, then run a `make clean` for
ARCH=arm.

Is the above (regarding lazy evaluation) not true for LDFLAGS_vmlinux?
I would have thought this would work:

diff --git a/arch/arm/boot/compressed/Makefile
b/arch/arm/boot/compressed/Makefile
index 00602a6fba04..9e7343ccc279 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -113,10 +113,9 @@ ccflags-y := -fpic $(call
cc-option,-mno-single-pic-base,) -fno-builtin \
 asflags-y := -DZIMAGE

 # Supply kernel BSS size to the decompressor via a linker symbol.
-KBSS_SZ = $(shell echo $$(($$($(NM) $(obj)/../../../../vmlinux | \
+LDFLAGS_vmlinux = --defsym _kernel_bss_size=$(shell echo $$(($$($(NM)
$(obj)/../../../../vmlinux | \
                sed -n -e 's/^\([^ ]*\) [AB] __bss_start$$/-0x\1/p' \
-                      -e 's/^\([^ ]*\) [AB] __bss_stop$$/+0x\1/p') )) )
-LDFLAGS_vmlinux = --defsym _kernel_bss_size=$(KBSS_SZ)
+                                        -e 's/^\([^ ]*\) [AB]
__bss_stop$$/+0x\1/p') )) )
Masahiro Yamada June 30, 2020, 6:18 p.m. UTC | #13
On Tue, Jun 30, 2020 at 7:39 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Mon, Jun 29, 2020 at 11:26 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Sat, Jun 27, 2020 at 4:59 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > On Sat, Jun 27, 2020 at 5:13 AM Nick Desaulniers
> > > <ndesaulniers@google.com> wrote:
> > > >
> > > > On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > > >
> > > > > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> > > > > index dba6a83bc349..93792b457b81 100644
> > > > > --- a/arch/x86/kernel/cpu/Makefile
> > > > > +++ b/arch/x86/kernel/cpu/Makefile
> > > > > @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
> > > > >  KCSAN_SANITIZE_common.o := n
> > > > >
> > > > >  # Make sure load_percpu_segment has no stackprotector
> > > > > -nostackp := $(call cc-option, -fno-stack-protector)
> > > > > -CFLAGS_common.o                := $(nostackp)
> > > > > +CFLAGS_common.o                := -fno-stack-protector
> > > >
> > > > Any time I see `:=` assignment to a CFLAGS variable, it's a red flag
> > > > for overwriting existing CFLAGS, which is a common source of bugs.  I
> > > > recognize the kernel is current a mix and match for:
> > > >
> > > > CFLAGS_<file>.o
> > > >
> > > > rules to either use `+=` or `:=`, but I wish we were consistent, and
> > > > consistent in our use of `+=`.  For those rules, is there a difference
> > > > between the use of `+=` and `:=` like there is for the more general
> > > > case of appending to KBUILD_CFLAGS?  If not, it's ok to match the
> > > > existing style, but it's curious to me in this patch to see a mixed
> > > > use of `+=` and `:=`.
> > >
> > >
> > > I think Kees mostly answered your question.
> > >
> > > Let me add some comments.
> > >
> > >
> > > '+=' is the most used in kernel Makefiles, but
> > > ':=' and '=' are also used.
> > >
> > > So, you are right, we are inconsistent.
> > > This applies to not only CFLAGS_<file>.o, but also obj-y, etc.
> > >
> > > For example,
> > > https://github.com/torvalds/linux/blob/v5.7/arch/arm64/kernel/Makefile#L15
> > > 'obj-y :=' works since it is the first assignment to obj-y in that file.
> > > 'obj-y +=' also works, of course.
> > >
> > > We can consistently use '+=' everywhere, but I do not send
> > > patches for churn.
> > >
> > >
> > > You can use any assignment operator to CFLAGS_<file>.o
> > > if it is the first assignment in the Makefile.
> > > Using '+=' is robust for future code insertion/removal, though.
> > >
> > >
> > > If the right-hand side contains variable references,
> > > there is important difference in the behavior.
> > >
> > > You may know two flavors in variables
> > > (https://www.gnu.org/software/make/manual/make.html#Flavors)
> >
> > Cool, thanks for all the info.  With that, I'm happy with this patch.
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> >
> > > CFLAGS_foo.o := $(call cc-option,-fno-stack-protector)
> > > The cc-option is expanded immediately when this line is parsed.
> > > (So, the compiler is invoked for 'make clean' too)
> > >
> > >
> > > CFLAGS_foo.o += $(call cc-option,-fno-stack-protector)
> > > If this is the first assignment in the file,
> > > '+=' act as '=', so the evaluation of cc-option
> > > is delayed until $(CFLAGS_foo.o) is expanded.
> > > (So, the compiler is NOT invoked for 'make clean')
> >
> > Ah, I think that may explain: I've been seeing the occasional warning
> > from $(NM) when running `make clean` for ARCH=arm, I'll bet that's
> > where this is coming from then.  Next time I reproduce it, I'll try to
> > find maybe where we're using `:=` or `=` with `$(NM)`.
> >
> > Maybe arch/arm/boot/compressed/Makefile, KBSS_SZ is evaluated for
> > `make clean`? (If you start an arm build, but kill it before vmlinux
> > is created, then `make clean` I suspect that KBSS_SZ is evaluated?)
>
> $ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 -j71
> $ rm vmlinux
> $ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 -j71 clean
> llvm-nm: error: arch/arm/boot/compressed/../../../../vmlinux: No such
> file or directory.

yeah, I had noticed this noise, but
I did not get around to digging into it.


> I suspect I see this from doing an ARCH=arm build, then building a
> different ARCH and killing the build before vmlinux is produced or
> `make clean` for a different ARCH, then run a `make clean` for
> ARCH=arm.
>
> Is the above (regarding lazy evaluation) not true for LDFLAGS_vmlinux?
> I would have thought this would work:


No, this does not work.

LDFLAGS_vmlinux is assigned by '=',
so it already has the lazy expansion flavor.


Unexporting LDFLAGS_vmlinux will fix it.
(I may write a better patch, though)



diff --git a/arch/arm/boot/compressed/Makefile
b/arch/arm/boot/compressed/Makefile
index 00602a6fba04..fab54b1c39aa 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -131,6 +131,8 @@ LDFLAGS_vmlinux += -X
 # Next argument is a linker script
 LDFLAGS_vmlinux += -T

+unexport LDFLAGS_vmlinux
+
 # For __aeabi_uidivmod
 lib1funcs = $(obj)/lib1funcs.o
Marco Elver July 1, 2020, 6:01 a.m. UTC | #14
On Sat, Jun 27, 2020 at 03:59AM +0900, Masahiro Yamada wrote:
> Some Makefiles already pass -fno-stack-protector unconditionally.
> For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.
> No problem report so far about hard-coding this option. So, we can
> assume all supported compilers know -fno-stack-protector.
> 
> GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)
> 
> Get rid of cc-option from -fno-stack-protector.
> 
> Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'.
> 
> Note:
> arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
> unconditionally, and second conditionally. I removed the second one.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
> 
>  Documentation/kbuild/kconfig-language.rst | 4 ++--
>  Makefile                                  | 2 +-
>  arch/Kconfig                              | 3 ---
>  arch/arm/boot/compressed/Makefile         | 3 +--
>  arch/mips/vdso/Makefile                   | 3 +--
>  arch/powerpc/kernel/Makefile              | 2 +-
>  arch/powerpc/platforms/powermac/Makefile  | 2 +-
>  arch/sparc/vdso/Makefile                  | 4 ++--
>  arch/um/Makefile                          | 3 +--
>  arch/x86/Makefile                         | 2 +-
>  arch/x86/boot/compressed/Makefile         | 2 +-
>  arch/x86/entry/vdso/Makefile              | 4 ++--
>  arch/x86/kernel/cpu/Makefile              | 3 +--
>  arch/x86/lib/Makefile                     | 2 +-
>  arch/x86/mm/Makefile                      | 7 +++----
>  arch/x86/power/Makefile                   | 3 +--
>  arch/x86/purgatory/Makefile               | 2 +-
>  arch/x86/um/vdso/Makefile                 | 2 +-
>  arch/x86/xen/Makefile                     | 5 ++---
>  drivers/firmware/efi/libstub/Makefile     | 2 +-
>  drivers/xen/Makefile                      | 3 +--
>  kernel/kcsan/Makefile                     | 3 +--

Is it possible that this patch drops the KCSAN portion? We have a patch
that is part of a series intended for 5.9 that also removes the
cc-option from -fno-stack-protector, but can't easily be dropped from
the surrounding series.

Please see: https://lkml.kernel.org/r/20200624190236.GA6603@paulmck-ThinkPad-P72

Thanks,
-- Marco
Masahiro Yamada July 1, 2020, 7:33 p.m. UTC | #15
On Tue, Jun 30, 2020 at 7:39 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Mon, Jun 29, 2020 at 11:26 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Sat, Jun 27, 2020 at 4:59 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > On Sat, Jun 27, 2020 at 5:13 AM Nick Desaulniers
> > > <ndesaulniers@google.com> wrote:
> > > >
> > > > On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > > >
> > > > > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> > > > > index dba6a83bc349..93792b457b81 100644
> > > > > --- a/arch/x86/kernel/cpu/Makefile
> > > > > +++ b/arch/x86/kernel/cpu/Makefile
> > > > > @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n
> > > > >  KCSAN_SANITIZE_common.o := n
> > > > >
> > > > >  # Make sure load_percpu_segment has no stackprotector
> > > > > -nostackp := $(call cc-option, -fno-stack-protector)
> > > > > -CFLAGS_common.o                := $(nostackp)
> > > > > +CFLAGS_common.o                := -fno-stack-protector
> > > >
> > > > Any time I see `:=` assignment to a CFLAGS variable, it's a red flag
> > > > for overwriting existing CFLAGS, which is a common source of bugs.  I
> > > > recognize the kernel is current a mix and match for:
> > > >
> > > > CFLAGS_<file>.o
> > > >
> > > > rules to either use `+=` or `:=`, but I wish we were consistent, and
> > > > consistent in our use of `+=`.  For those rules, is there a difference
> > > > between the use of `+=` and `:=` like there is for the more general
> > > > case of appending to KBUILD_CFLAGS?  If not, it's ok to match the
> > > > existing style, but it's curious to me in this patch to see a mixed
> > > > use of `+=` and `:=`.
> > >
> > >
> > > I think Kees mostly answered your question.
> > >
> > > Let me add some comments.
> > >
> > >
> > > '+=' is the most used in kernel Makefiles, but
> > > ':=' and '=' are also used.
> > >
> > > So, you are right, we are inconsistent.
> > > This applies to not only CFLAGS_<file>.o, but also obj-y, etc.
> > >
> > > For example,
> > > https://github.com/torvalds/linux/blob/v5.7/arch/arm64/kernel/Makefile#L15
> > > 'obj-y :=' works since it is the first assignment to obj-y in that file.
> > > 'obj-y +=' also works, of course.
> > >
> > > We can consistently use '+=' everywhere, but I do not send
> > > patches for churn.
> > >
> > >
> > > You can use any assignment operator to CFLAGS_<file>.o
> > > if it is the first assignment in the Makefile.
> > > Using '+=' is robust for future code insertion/removal, though.
> > >
> > >
> > > If the right-hand side contains variable references,
> > > there is important difference in the behavior.
> > >
> > > You may know two flavors in variables
> > > (https://www.gnu.org/software/make/manual/make.html#Flavors)
> >
> > Cool, thanks for all the info.  With that, I'm happy with this patch.
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> >
> > > CFLAGS_foo.o := $(call cc-option,-fno-stack-protector)
> > > The cc-option is expanded immediately when this line is parsed.
> > > (So, the compiler is invoked for 'make clean' too)
> > >
> > >
> > > CFLAGS_foo.o += $(call cc-option,-fno-stack-protector)
> > > If this is the first assignment in the file,
> > > '+=' act as '=', so the evaluation of cc-option
> > > is delayed until $(CFLAGS_foo.o) is expanded.
> > > (So, the compiler is NOT invoked for 'make clean')
> >
> > Ah, I think that may explain: I've been seeing the occasional warning
> > from $(NM) when running `make clean` for ARCH=arm, I'll bet that's
> > where this is coming from then.  Next time I reproduce it, I'll try to
> > find maybe where we're using `:=` or `=` with `$(NM)`.
> >
> > Maybe arch/arm/boot/compressed/Makefile, KBSS_SZ is evaluated for
> > `make clean`? (If you start an arm build, but kill it before vmlinux
> > is created, then `make clean` I suspect that KBSS_SZ is evaluated?)
>
> $ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 -j71
> $ rm vmlinux
> $ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 -j71 clean
> llvm-nm: error: arch/arm/boot/compressed/../../../../vmlinux: No such
> file or directory.
>
> I suspect I see this from doing an ARCH=arm build, then building a
> different ARCH and killing the build before vmlinux is produced or
> `make clean` for a different ARCH, then run a `make clean` for
> ARCH=arm.
>
> Is the above (regarding lazy evaluation) not true for LDFLAGS_vmlinux?
> I would have thought this would work:
>


I described why this error message is displayed:

https://patchwork.kernel.org/patch/11637129/

Patch
diff mbox series

diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
index a1601ec3317b..2538e7cb08e6 100644
--- a/Documentation/kbuild/kconfig-language.rst
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -540,8 +540,8 @@  followed by a test macro::
 If you need to expose a compiler capability to makefiles and/or C source files,
 `CC_HAS_` is the recommended prefix for the config option::
 
-  config CC_HAS_STACKPROTECTOR_NONE
-	def_bool $(cc-option,-fno-stack-protector)
+  config CC_HAS_ASM_GOTO
+	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
 
 Build as module only
 ~~~~~~~~~~~~~~~~~~~~
diff --git a/Makefile b/Makefile
index 5496a32dffa6..73948798ce3f 100644
--- a/Makefile
+++ b/Makefile
@@ -762,7 +762,7 @@  ifneq ($(CONFIG_FRAME_WARN),0)
 KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
 endif
 
-stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
+stackp-flags-y                                    := -fno-stack-protector
 stackp-flags-$(CONFIG_STACKPROTECTOR)             := -fstack-protector
 stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
 
diff --git a/arch/Kconfig b/arch/Kconfig
index 8cc35dc556c7..1ea61290900a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -478,9 +478,6 @@  config HAVE_STACKPROTECTOR
 	  An arch should select this symbol if:
 	  - it has implemented a stack canary (e.g. __stack_chk_guard)
 
-config CC_HAS_STACKPROTECTOR_NONE
-	def_bool $(cc-option,-fno-stack-protector)
-
 config STACKPROTECTOR
 	bool "Stack Protector buffer overflow detection"
 	depends on HAVE_STACKPROTECTOR
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 00602a6fba04..cb7a56c6723c 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -84,9 +84,8 @@  endif
 
 # -fstack-protector-strong triggers protection checks in this code,
 # but it is being used too early to link to meaningful stack_chk logic.
-nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
 $(foreach o, $(libfdt_objs) atags_to_fdt.o, \
-	$(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y)))
+	$(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector))
 
 # These were previously generated C files. When you are building the kernel
 # with O=, make sure to remove the stale files in the output tree. Otherwise,
diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index 2e64c7600eea..57fe83235281 100644
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -35,8 +35,7 @@  cflags-vdso := $(ccflags-vdso) \
 	-O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
 	-mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
 	-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
-	$(call cc-option, -fno-asynchronous-unwind-tables) \
-	$(call cc-option, -fno-stack-protector)
+	$(call cc-option, -fno-asynchronous-unwind-tables)
 aflags-vdso := $(ccflags-vdso) \
 	-D__ASSEMBLY__ -Wa,-gdwarf-2
 
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 244542ae2a91..3a83f2b876a5 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -16,7 +16,7 @@  CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 
-CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
+CFLAGS_prom_init.o += -fno-stack-protector
 CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING
 CFLAGS_prom_init.o += -ffreestanding
 
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index f4247ade71ca..cf85f0662d0d 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -1,6 +1,6 @@ 
 # SPDX-License-Identifier: GPL-2.0
 CFLAGS_bootx_init.o  		+= -fPIC
-CFLAGS_bootx_init.o  		+= $(call cc-option, -fno-stack-protector)
+CFLAGS_bootx_init.o		+= -fno-stack-protector
 
 KASAN_SANITIZE_bootx_init.o := n
 
diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
index 708cb6304c2d..f44355e46f31 100644
--- a/arch/sparc/vdso/Makefile
+++ b/arch/sparc/vdso/Makefile
@@ -54,7 +54,7 @@  $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
 # optimize sibling calls.
 #
 CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \
-       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
+       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
        -fno-omit-frame-pointer -foptimize-sibling-calls \
        -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
 
@@ -93,7 +93,7 @@  KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic
-KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
+KBUILD_CFLAGS_32 += -fno-stack-protector
 KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
 KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
 KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
diff --git a/arch/um/Makefile b/arch/um/Makefile
index 3f27aa3ec0a6..1cea46ff9bb7 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -121,8 +121,7 @@  LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
 LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
 
 CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
-	$(call cc-option, -fno-stack-protector,) \
-	$(call cc-option, -fno-stack-protector-all,)
+	-fno-stack-protector $(call cc-option, -fno-stack-protector-all)
 
 # Options used by linker script
 export LDS_START      := $(START)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 00e378de8bc0..89c3cdfba753 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -37,7 +37,7 @@  REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \
 		   -mno-mmx -mno-sse
 
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
-REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
+REALMODE_CFLAGS += -fno-stack-protector
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
 export REALMODE_CFLAGS
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 7619742f91c9..c88a31569a5e 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -36,7 +36,7 @@  cflags-$(CONFIG_X86_64) := -mcmodel=small
 KBUILD_CFLAGS += $(cflags-y)
 KBUILD_CFLAGS += -mno-mmx -mno-sse
 KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
-KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
+KBUILD_CFLAGS += -fno-stack-protector
 KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
 KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
 KBUILD_CFLAGS += -Wno-pointer-sign
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 04e65f0698f6..215376d975a2 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -82,7 +82,7 @@  $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
 # optimize sibling calls.
 #
 CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
-       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
+       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
        -fno-omit-frame-pointer -foptimize-sibling-calls \
        -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
 
@@ -151,7 +151,7 @@  KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
-KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
+KBUILD_CFLAGS_32 += -fno-stack-protector
 KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
 KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
 KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index dba6a83bc349..93792b457b81 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -17,8 +17,7 @@  KCOV_INSTRUMENT_perf_event.o := n
 KCSAN_SANITIZE_common.o := n
 
 # Make sure load_percpu_segment has no stackprotector
-nostackp := $(call cc-option, -fno-stack-protector)
-CFLAGS_common.o		:= $(nostackp)
+CFLAGS_common.o		:= -fno-stack-protector
 
 obj-y			:= cacheinfo.o scattered.o topology.o
 obj-y			+= common.o
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 6110bce7237b..d46fff11f06f 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -24,7 +24,7 @@  ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_cmdline.o = -pg
 endif
 
-CFLAGS_cmdline.o := $(call cc-option, -fno-stack-protector)
+CFLAGS_cmdline.o := -fno-stack-protector
 endif
 
 inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index f7fd0e868c9c..5864219221ca 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -22,10 +22,9 @@  obj-y				:=  init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
 obj-y				+= pat/
 
 # Make sure __phys_addr has no stackprotector
-nostackp := $(call cc-option, -fno-stack-protector)
-CFLAGS_physaddr.o		:= $(nostackp)
-CFLAGS_setup_nx.o		:= $(nostackp)
-CFLAGS_mem_encrypt_identity.o	:= $(nostackp)
+CFLAGS_physaddr.o		:= -fno-stack-protector
+CFLAGS_setup_nx.o		:= -fno-stack-protector
+CFLAGS_mem_encrypt_identity.o	:= -fno-stack-protector
 
 CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace
 
diff --git a/arch/x86/power/Makefile b/arch/x86/power/Makefile
index 37923d715741..6907b523e856 100644
--- a/arch/x86/power/Makefile
+++ b/arch/x86/power/Makefile
@@ -3,8 +3,7 @@  OBJECT_FILES_NON_STANDARD_hibernate_asm_$(BITS).o := y
 
 # __restore_processor_state() restores %gs after S3 resume and so should not
 # itself be stack-protected
-nostackp := $(call cc-option, -fno-stack-protector)
-CFLAGS_cpu.o	:= $(nostackp)
+CFLAGS_cpu.o	:= -fno-stack-protector
 
 obj-$(CONFIG_PM_SLEEP)		+= cpu.o
 obj-$(CONFIG_HIBERNATION)	+= hibernate_$(BITS).o hibernate_asm_$(BITS).o hibernate.o
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 088bd764e0b7..183ac60e5990 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -34,7 +34,7 @@  KCOV_INSTRUMENT := n
 PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
 PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
 PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
-PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)
+PURGATORY_CFLAGS += -fno-stack-protector
 
 # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
 # in turn leaves some undefined symbols like __fentry__ in purgatory and not
diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
index 0caddd6acb22..5943387e3f35 100644
--- a/arch/x86/um/vdso/Makefile
+++ b/arch/x86/um/vdso/Makefile
@@ -42,7 +42,7 @@  $(obj)/%.so: $(obj)/%.so.dbg FORCE
 # optimize sibling calls.
 #
 CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
-       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
+       $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \
        -fno-omit-frame-pointer -foptimize-sibling-calls
 
 $(vobjs): KBUILD_CFLAGS += $(CFL)
diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index 084de77a109e..5f1db522d06b 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -9,9 +9,8 @@  CFLAGS_REMOVE_irq.o = -pg
 endif
 
 # Make sure early boot has no stackprotector
-nostackp := $(call cc-option, -fno-stack-protector)
-CFLAGS_enlighten_pv.o		:= $(nostackp)
-CFLAGS_mmu_pv.o			:= $(nostackp)
+CFLAGS_enlighten_pv.o		:= -fno-stack-protector
+CFLAGS_mmu_pv.o			:= -fno-stack-protector
 
 obj-y				+= enlighten.o
 obj-y				+= mmu.o
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 75daaf20374e..f8418763cd79 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -29,7 +29,7 @@  KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
 				   -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \
 				   -D__NO_FORTIFY \
 				   $(call cc-option,-ffreestanding) \
-				   $(call cc-option,-fno-stack-protector) \
+				   -fno-stack-protector \
 				   $(call cc-option,-fno-addrsig) \
 				   -D__DISABLE_EXPORTS
 
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0d322f3d90cd..c25c9a699b48 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -5,8 +5,7 @@  obj-y	+= mem-reservation.o
 obj-y	+= events/
 obj-y	+= xenbus/
 
-nostackp := $(call cc-option, -fno-stack-protector)
-CFLAGS_features.o			:= $(nostackp)
+CFLAGS_features.o			:= -fno-stack-protector
 
 dom0-$(CONFIG_ARM64) += arm-device.o
 dom0-$(CONFIG_PCI) += pci.o
diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index d4999b38d1be..d111f32bd5fd 100644
--- a/kernel/kcsan/Makefile
+++ b/kernel/kcsan/Makefile
@@ -7,8 +7,7 @@  CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
 
-CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
-	$(call cc-option,-fno-stack-protector,)
+CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) -fno-stack-protector
 
 obj-y := core.o debugfs.o report.o
 obj-$(CONFIG_KCSAN_SELFTEST) += test.o
diff --git a/lib/Makefile b/lib/Makefile
index b1c42c10073b..0cda70649f1c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -22,7 +22,7 @@  KCOV_INSTRUMENT_fault-inject.o := n
 ifdef CONFIG_AMD_MEM_ENCRYPT
 KASAN_SANITIZE_string.o := n
 
-CFLAGS_string.o := $(call cc-option, -fno-stack-protector)
+CFLAGS_string.o := -fno-stack-protector
 endif
 
 # Used by KCSAN while enabled, avoid recursion.
@@ -300,7 +300,7 @@  endif
 UBSAN_SANITIZE_ubsan.o := n
 KASAN_SANITIZE_ubsan.o := n
 KCSAN_SANITIZE_ubsan.o := n
-CFLAGS_ubsan.o := $(call cc-option, -fno-stack-protector) $(DISABLE_STACKLEAK_PLUGIN)
+CFLAGS_ubsan.o := -fno-stack-protector $(DISABLE_STACKLEAK_PLUGIN)
 
 obj-$(CONFIG_SBITMAP) += sbitmap.o
 
diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index d532c2587731..370d970e5ab5 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -16,7 +16,7 @@  CFLAGS_REMOVE_tags_report.o = $(CC_FLAGS_FTRACE)
 # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
 # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
 CC_FLAGS_KASAN_RUNTIME := $(call cc-option, -fno-conserve-stack)
-CC_FLAGS_KASAN_RUNTIME += $(call cc-option, -fno-stack-protector)
+CC_FLAGS_KASAN_RUNTIME += -fno-stack-protector
 # Disable branch tracing to avoid recursion.
 CC_FLAGS_KASAN_RUNTIME += -DDISABLE_BRANCH_PROFILING