| Message ID | 20171120141259.6724-1-ard.biesheuvel@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 20 November 2017 at 14:12, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > When building the arm64 kernel with both CONFIG_ARM64_MODULE_PLTS and > CONFIG_DYNAMIC_FTRACE enabled, the ftrace-mod.o object file is built > with the kernel and contains a trampoline that is linked into each > module, so that modules can be loaded far away from the kernel and > still reach the ftrace entry point in the core kernel with an ordinary > relative branch, as is emitted by the compiler instrumentation code > dynamic ftrace relies on. > > In order to be able to build out of tree modules, this object file > needs to be included into the linux-headers or linux-devel packages, > which is undesirable, as it makes arm64 a special case (although a > precedent does exist for 32-bit PPC). > > Given that the trampoline only consists of two instructions, let's > not bother with a source or object file for it, and simply patch in > these instructions whenever the trampoline is being populated. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > v2: populate the two trampoline instruction slots from the ftrace code so > there is no longer a need to have a template .o or .S in the first place > don't use a separate linker scripts for ftrace+PLTs > Actually, I will respin this to reuse the existing plt_entry code, given that it is so similar to the ftrace trampoline. > arch/arm64/Makefile | 3 --- > arch/arm64/kernel/Makefile | 3 --- > arch/arm64/kernel/ftrace-mod.S | 18 ------------------ > arch/arm64/kernel/ftrace-trampoline.h | 18 ++++++++++++++++++ > arch/arm64/kernel/ftrace.c | 16 ++++++++++------ > arch/arm64/kernel/module-plts.c | 14 ++++++++++++++ > arch/arm64/kernel/module.lds | 1 + > 7 files changed, 43 insertions(+), 30 deletions(-) > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index b35788c909f1..b481b4a7c011 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -83,9 +83,6 @@ endif > > ifeq ($(CONFIG_ARM64_MODULE_PLTS),y) > KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/module.lds > -ifeq ($(CONFIG_DYNAMIC_FTRACE),y) > -KBUILD_LDFLAGS_MODULE += $(objtree)/arch/arm64/kernel/ftrace-mod.o > -endif > endif > > # Default value > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index 8265dd790895..067baace74a0 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -61,6 +61,3 @@ extra-y += $(head-y) vmlinux.lds > ifeq ($(CONFIG_DEBUG_EFI),y) > AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\"" > endif > - > -# will be included by each individual module but not by the core kernel itself > -extra-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o > diff --git a/arch/arm64/kernel/ftrace-mod.S b/arch/arm64/kernel/ftrace-mod.S > deleted file mode 100644 > index 00c4025be4ff..000000000000 > --- a/arch/arm64/kernel/ftrace-mod.S > +++ /dev/null > @@ -1,18 +0,0 @@ > -/* > - * Copyright (C) 2017 Linaro Ltd <ard.biesheuvel@linaro.org> > - * > - * This program is free software; you can redistribute it and/or modify > - * it under the terms of the GNU General Public License version 2 as > - * published by the Free Software Foundation. > - */ > - > -#include <linux/linkage.h> > -#include <asm/assembler.h> > - > - .section ".text.ftrace_trampoline", "ax" > - .align 3 > -0: .quad 0 > -__ftrace_trampoline: > - ldr x16, 0b > - br x16 > -ENDPROC(__ftrace_trampoline) > diff --git a/arch/arm64/kernel/ftrace-trampoline.h b/arch/arm64/kernel/ftrace-trampoline.h > new file mode 100644 > index 000000000000..caf8434ca52a > --- /dev/null > +++ b/arch/arm64/kernel/ftrace-trampoline.h > @@ -0,0 +1,18 @@ > +/* > + * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org> > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License version 2 as > + * published by the Free Software Foundation. > + */ > + > +#include <linux/types.h> > + > +#define FTRACE_TRAMPOLINE_LDR cpu_to_le32(0x58ffffd0) > +#define FTRACE_TRAMPOLINE_BR cpu_to_le32(0xd61f0200) > + > +struct ftrace_trampoline { > + u64 literal; /* 0: .quad 0x0 */ > + __le32 ldr; /* ldr x16, 0b */ > + __le32 br; /* br x16 */ > +}; > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index c13b1fca0e5b..2198b5a48871 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -19,6 +19,8 @@ > #include <asm/ftrace.h> > #include <asm/insn.h> > > +#include "ftrace-trampoline.h" > + > #ifdef CONFIG_DYNAMIC_FTRACE > /* > * Replace a single instruction, which may be a branch or NOP. > @@ -76,7 +78,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) > > if (offset < -SZ_128M || offset >= SZ_128M) { > #ifdef CONFIG_ARM64_MODULE_PLTS > - unsigned long *trampoline; > + struct ftrace_trampoline *trampoline; > struct module *mod; > > /* > @@ -104,22 +106,24 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) > * is added in the future, but for now, the pr_err() below > * deals with a theoretical issue only. > */ > - trampoline = (unsigned long *)mod->arch.ftrace_trampoline; > - if (trampoline[0] != addr) { > - if (trampoline[0] != 0) { > + trampoline = (void *)mod->arch.ftrace_trampoline; > + if (trampoline->literal != addr) { > + if (trampoline->literal != 0) { > pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n"); > return -EINVAL; > } > > /* point the trampoline to our ftrace entry point */ > module_disable_ro(mod); > - trampoline[0] = addr; > + trampoline->literal = addr; > + trampoline->ldr = FTRACE_TRAMPOLINE_LDR; > + trampoline->br = FTRACE_TRAMPOLINE_BR; > module_enable_ro(mod, true); > > /* update trampoline before patching in the branch */ > smp_wmb(); > } > - addr = (unsigned long)&trampoline[1]; > + addr = (unsigned long)&trampoline->ldr; > #else /* CONFIG_ARM64_MODULE_PLTS */ > return -EINVAL; > #endif /* CONFIG_ARM64_MODULE_PLTS */ > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > index d05dbe658409..c8fe9c98abc4 100644 > --- a/arch/arm64/kernel/module-plts.c > +++ b/arch/arm64/kernel/module-plts.c > @@ -11,6 +11,8 @@ > #include <linux/module.h> > #include <linux/sort.h> > > +#include "ftrace-trampoline.h" > + > struct plt_entry { > /* > * A program that conforms to the AArch64 Procedure Call Standard > @@ -154,6 +156,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > unsigned long core_plts = 0; > unsigned long init_plts = 0; > Elf64_Sym *syms = NULL; > + Elf_Shdr *tramp = NULL; > int i; > > /* > @@ -165,6 +168,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > mod->arch.core.plt = sechdrs + i; > else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) > mod->arch.init.plt = sechdrs + i; > + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && > + !strcmp(secstrings + sechdrs[i].sh_name, > + ".text.ftrace_trampoline")) > + tramp = sechdrs + i; > else if (sechdrs[i].sh_type == SHT_SYMTAB) > syms = (Elf64_Sym *)sechdrs[i].sh_addr; > } > @@ -215,5 +222,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > mod->arch.init.plt_num_entries = 0; > mod->arch.init.plt_max_entries = init_plts; > > + if (tramp) { > + tramp->sh_type = SHT_NOBITS; > + tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC; > + tramp->sh_addralign = __alignof__(struct ftrace_trampoline); > + tramp->sh_size = sizeof(struct ftrace_trampoline); > + } > + > return 0; > } > diff --git a/arch/arm64/kernel/module.lds b/arch/arm64/kernel/module.lds > index f7c9781a9d48..22e36a21c113 100644 > --- a/arch/arm64/kernel/module.lds > +++ b/arch/arm64/kernel/module.lds > @@ -1,4 +1,5 @@ > SECTIONS { > .plt (NOLOAD) : { BYTE(0) } > .init.plt (NOLOAD) : { BYTE(0) } > + .text.ftrace_trampoline (NOLOAD) : { BYTE(0) } > } > -- > 2.11.0 >
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index b35788c909f1..b481b4a7c011 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -83,9 +83,6 @@ endif ifeq ($(CONFIG_ARM64_MODULE_PLTS),y) KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/module.lds -ifeq ($(CONFIG_DYNAMIC_FTRACE),y) -KBUILD_LDFLAGS_MODULE += $(objtree)/arch/arm64/kernel/ftrace-mod.o -endif endif # Default value diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 8265dd790895..067baace74a0 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -61,6 +61,3 @@ extra-y += $(head-y) vmlinux.lds ifeq ($(CONFIG_DEBUG_EFI),y) AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\"" endif - -# will be included by each individual module but not by the core kernel itself -extra-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o diff --git a/arch/arm64/kernel/ftrace-mod.S b/arch/arm64/kernel/ftrace-mod.S deleted file mode 100644 index 00c4025be4ff..000000000000 --- a/arch/arm64/kernel/ftrace-mod.S +++ /dev/null @@ -1,18 +0,0 @@ -/* - * Copyright (C) 2017 Linaro Ltd <ard.biesheuvel@linaro.org> - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 as - * published by the Free Software Foundation. - */ - -#include <linux/linkage.h> -#include <asm/assembler.h> - - .section ".text.ftrace_trampoline", "ax" - .align 3 -0: .quad 0 -__ftrace_trampoline: - ldr x16, 0b - br x16 -ENDPROC(__ftrace_trampoline) diff --git a/arch/arm64/kernel/ftrace-trampoline.h b/arch/arm64/kernel/ftrace-trampoline.h new file mode 100644 index 000000000000..caf8434ca52a --- /dev/null +++ b/arch/arm64/kernel/ftrace-trampoline.h @@ -0,0 +1,18 @@ +/* + * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#include <linux/types.h> + +#define FTRACE_TRAMPOLINE_LDR cpu_to_le32(0x58ffffd0) +#define FTRACE_TRAMPOLINE_BR cpu_to_le32(0xd61f0200) + +struct ftrace_trampoline { + u64 literal; /* 0: .quad 0x0 */ + __le32 ldr; /* ldr x16, 0b */ + __le32 br; /* br x16 */ +}; diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index c13b1fca0e5b..2198b5a48871 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -19,6 +19,8 @@ #include <asm/ftrace.h> #include <asm/insn.h> +#include "ftrace-trampoline.h" + #ifdef CONFIG_DYNAMIC_FTRACE /* * Replace a single instruction, which may be a branch or NOP. @@ -76,7 +78,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) if (offset < -SZ_128M || offset >= SZ_128M) { #ifdef CONFIG_ARM64_MODULE_PLTS - unsigned long *trampoline; + struct ftrace_trampoline *trampoline; struct module *mod; /* @@ -104,22 +106,24 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) * is added in the future, but for now, the pr_err() below * deals with a theoretical issue only. */ - trampoline = (unsigned long *)mod->arch.ftrace_trampoline; - if (trampoline[0] != addr) { - if (trampoline[0] != 0) { + trampoline = (void *)mod->arch.ftrace_trampoline; + if (trampoline->literal != addr) { + if (trampoline->literal != 0) { pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n"); return -EINVAL; } /* point the trampoline to our ftrace entry point */ module_disable_ro(mod); - trampoline[0] = addr; + trampoline->literal = addr; + trampoline->ldr = FTRACE_TRAMPOLINE_LDR; + trampoline->br = FTRACE_TRAMPOLINE_BR; module_enable_ro(mod, true); /* update trampoline before patching in the branch */ smp_wmb(); } - addr = (unsigned long)&trampoline[1]; + addr = (unsigned long)&trampoline->ldr; #else /* CONFIG_ARM64_MODULE_PLTS */ return -EINVAL; #endif /* CONFIG_ARM64_MODULE_PLTS */ diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c index d05dbe658409..c8fe9c98abc4 100644 --- a/arch/arm64/kernel/module-plts.c +++ b/arch/arm64/kernel/module-plts.c @@ -11,6 +11,8 @@ #include <linux/module.h> #include <linux/sort.h> +#include "ftrace-trampoline.h" + struct plt_entry { /* * A program that conforms to the AArch64 Procedure Call Standard @@ -154,6 +156,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, unsigned long core_plts = 0; unsigned long init_plts = 0; Elf64_Sym *syms = NULL; + Elf_Shdr *tramp = NULL; int i; /* @@ -165,6 +168,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, mod->arch.core.plt = sechdrs + i; else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) mod->arch.init.plt = sechdrs + i; + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && + !strcmp(secstrings + sechdrs[i].sh_name, + ".text.ftrace_trampoline")) + tramp = sechdrs + i; else if (sechdrs[i].sh_type == SHT_SYMTAB) syms = (Elf64_Sym *)sechdrs[i].sh_addr; } @@ -215,5 +222,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, mod->arch.init.plt_num_entries = 0; mod->arch.init.plt_max_entries = init_plts; + if (tramp) { + tramp->sh_type = SHT_NOBITS; + tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + tramp->sh_addralign = __alignof__(struct ftrace_trampoline); + tramp->sh_size = sizeof(struct ftrace_trampoline); + } + return 0; } diff --git a/arch/arm64/kernel/module.lds b/arch/arm64/kernel/module.lds index f7c9781a9d48..22e36a21c113 100644 --- a/arch/arm64/kernel/module.lds +++ b/arch/arm64/kernel/module.lds @@ -1,4 +1,5 @@ SECTIONS { .plt (NOLOAD) : { BYTE(0) } .init.plt (NOLOAD) : { BYTE(0) } + .text.ftrace_trampoline (NOLOAD) : { BYTE(0) } }
When building the arm64 kernel with both CONFIG_ARM64_MODULE_PLTS and CONFIG_DYNAMIC_FTRACE enabled, the ftrace-mod.o object file is built with the kernel and contains a trampoline that is linked into each module, so that modules can be loaded far away from the kernel and still reach the ftrace entry point in the core kernel with an ordinary relative branch, as is emitted by the compiler instrumentation code dynamic ftrace relies on. In order to be able to build out of tree modules, this object file needs to be included into the linux-headers or linux-devel packages, which is undesirable, as it makes arm64 a special case (although a precedent does exist for 32-bit PPC). Given that the trampoline only consists of two instructions, let's not bother with a source or object file for it, and simply patch in these instructions whenever the trampoline is being populated. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- v2: populate the two trampoline instruction slots from the ftrace code so there is no longer a need to have a template .o or .S in the first place don't use a separate linker scripts for ftrace+PLTs arch/arm64/Makefile | 3 --- arch/arm64/kernel/Makefile | 3 --- arch/arm64/kernel/ftrace-mod.S | 18 ------------------ arch/arm64/kernel/ftrace-trampoline.h | 18 ++++++++++++++++++ arch/arm64/kernel/ftrace.c | 16 ++++++++++------ arch/arm64/kernel/module-plts.c | 14 ++++++++++++++ arch/arm64/kernel/module.lds | 1 + 7 files changed, 43 insertions(+), 30 deletions(-)