[v3,1/2] initmem: introduce CONFIG_INIT_ALL_MEMORY and CONFIG_INIT_ALL_STACK
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Message ID 20190408170418.148554-2-glider@google.com
State New
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Series
  • RFC: introduce CONFIG_INIT_ALL_MEMORY
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Commit Message

Alexander Potapenko April 8, 2019, 5:04 p.m. UTC
CONFIG_INIT_ALL_MEMORY is going to be an umbrella config for options
that force heap and stack initialization.
The rationale behind doing so is to reduce the severity of bugs caused
by using uninitialized memory.

CONFIG_INIT_ALL_STACK turns on stack initialization based on
-ftrivial-auto-var-init in Clang builds and on
-fplugin-arg-structleak_plugin-byref-all in GCC builds.

-ftrivial-auto-var-init is a Clang flag that provides trivial
initializers for uninitialized local variables, variable fields and
padding.

It has three possible values:
  pattern - uninitialized locals are filled with a fixed pattern
    (mostly 0xAA on 64-bit platforms, see https://reviews.llvm.org/D54604
    for more details) likely to cause crashes when uninitialized value is
    used;
  zero (it's still debated whether this flag makes it to the official
    Clang release) - uninitialized locals are filled with zeroes;
  uninitialized (default) - uninitialized locals are left intact.

The proposed config builds the kernel with
-ftrivial-auto-var-init=pattern.

Developers have the possibility to opt-out of this feature on a
per-variable basis by using __attribute__((uninitialized)).

For GCC builds, CONFIG_INIT_ALL_STACK is simply wired up to
CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. No opt-out is possible at the
moment.

Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Sandeep Patil <sspatil@android.com>
Cc: linux-security-module@vger.kernel.org
Cc: linux-kbuild@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
---
 v2:
  - addressed Kees Cook's comments: added GCC support
 v3: addressed Masahiro Yamada's comments:
  - dropped per-file opt-out mechanism
  - fixed GCC_PLUGINS dependencies
---
 Makefile                 |  3 ++-
 scripts/Makefile.initmem | 10 ++++++++++
 security/Kconfig         |  1 +
 security/Kconfig.initmem | 29 +++++++++++++++++++++++++++++
 4 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 scripts/Makefile.initmem
 create mode 100644 security/Kconfig.initmem

Comments

Randy Dunlap April 8, 2019, 10:15 p.m. UTC | #1
On 4/8/19 10:04 AM, Alexander Potapenko wrote:
> diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
> new file mode 100644
> index 000000000000..5e49a55382ad
> --- /dev/null
> +++ b/security/Kconfig.initmem
> @@ -0,0 +1,29 @@
> +menu "Initialize all memory"
> +
> +config CC_HAS_AUTO_VAR_INIT
> +	def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
> +
> +config INIT_ALL_MEMORY
> +	bool "Initialize all memory"
> +	default n
> +	help
> +	  Enforce memory initialization to mitigate infoleaks and make
> +	  the control-flow bugs depending on uninitialized values more
> +	  deterministic.
> +
> +if INIT_ALL_MEMORY
> +
> +config INIT_ALL_STACK
> +	bool "Initialize all stack"
> +	depends on INIT_ALL_MEMORY

This "depends on" is redundant with the "if INIT_ALL_MEMORY" above it.

Similar comment for patch 2/2 and INIT_ALL_HEAP.

> +	depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
> +	select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
> +	select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
> +	select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
> +	default y
> +	help
> +	  Initialize uninitialized stack data with a fixed pattern
> +	  (0x00 in GCC, 0xAA in Clang).
> +
> +endif # INIT_ALL_MEMORY
> +endmenu
Alexander Potapenko April 9, 2019, 8:29 a.m. UTC | #2
On Tue, Apr 9, 2019 at 12:15 AM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> On 4/8/19 10:04 AM, Alexander Potapenko wrote:
> > diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
> > new file mode 100644
> > index 000000000000..5e49a55382ad
> > --- /dev/null
> > +++ b/security/Kconfig.initmem
> > @@ -0,0 +1,29 @@
> > +menu "Initialize all memory"
> > +
> > +config CC_HAS_AUTO_VAR_INIT
> > +     def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
> > +
> > +config INIT_ALL_MEMORY
> > +     bool "Initialize all memory"
> > +     default n
> > +     help
> > +       Enforce memory initialization to mitigate infoleaks and make
> > +       the control-flow bugs depending on uninitialized values more
> > +       deterministic.
> > +
> > +if INIT_ALL_MEMORY
> > +
> > +config INIT_ALL_STACK
> > +     bool "Initialize all stack"
> > +     depends on INIT_ALL_MEMORY
>
> This "depends on" is redundant with the "if INIT_ALL_MEMORY" above it.
Ack, thank you!
> Similar comment for patch 2/2 and INIT_ALL_HEAP.
>
> > +     depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
> > +     select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
> > +     select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
> > +     select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
> > +     default y
> > +     help
> > +       Initialize uninitialized stack data with a fixed pattern
> > +       (0x00 in GCC, 0xAA in Clang).
> > +
> > +endif # INIT_ALL_MEMORY
> > +endmenu
>
>
> --
> ~Randy
Masahiro Yamada April 9, 2019, 8:37 a.m. UTC | #3
On Tue, Apr 9, 2019 at 2:04 AM Alexander Potapenko <glider@google.com> wrote:
>
> CONFIG_INIT_ALL_MEMORY is going to be an umbrella config for options
> that force heap and stack initialization.
> The rationale behind doing so is to reduce the severity of bugs caused
> by using uninitialized memory.
>
> CONFIG_INIT_ALL_STACK turns on stack initialization based on
> -ftrivial-auto-var-init in Clang builds and on
> -fplugin-arg-structleak_plugin-byref-all in GCC builds.
>
> -ftrivial-auto-var-init is a Clang flag that provides trivial
> initializers for uninitialized local variables, variable fields and
> padding.
>
> It has three possible values:
>   pattern - uninitialized locals are filled with a fixed pattern
>     (mostly 0xAA on 64-bit platforms, see https://reviews.llvm.org/D54604
>     for more details) likely to cause crashes when uninitialized value is
>     used;
>   zero (it's still debated whether this flag makes it to the official
>     Clang release) - uninitialized locals are filled with zeroes;
>   uninitialized (default) - uninitialized locals are left intact.
>
> The proposed config builds the kernel with
> -ftrivial-auto-var-init=pattern.
>
> Developers have the possibility to opt-out of this feature on a
> per-variable basis by using __attribute__((uninitialized)).
>
> For GCC builds, CONFIG_INIT_ALL_STACK is simply wired up to
> CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. No opt-out is possible at the
> moment.
>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: James Morris <jmorris@namei.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Kostya Serebryany <kcc@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Sandeep Patil <sspatil@android.com>
> Cc: linux-security-module@vger.kernel.org
> Cc: linux-kbuild@vger.kernel.org
> Cc: kernel-hardening@lists.openwall.com
> ---
>  v2:
>   - addressed Kees Cook's comments: added GCC support
>  v3: addressed Masahiro Yamada's comments:
>   - dropped per-file opt-out mechanism
>   - fixed GCC_PLUGINS dependencies
> ---
>  Makefile                 |  3 ++-
>  scripts/Makefile.initmem | 10 ++++++++++
>  security/Kconfig         |  1 +
>  security/Kconfig.initmem | 29 +++++++++++++++++++++++++++++
>  4 files changed, 42 insertions(+), 1 deletion(-)
>  create mode 100644 scripts/Makefile.initmem
>  create mode 100644 security/Kconfig.initmem
>
> diff --git a/Makefile b/Makefile
> index f070e0d65186..028ca37878fd 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -448,7 +448,7 @@ export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
>
>  export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
>  export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
> -export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
> +export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_INITMEM
>  export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
>  export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
>  export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
> @@ -840,6 +840,7 @@ KBUILD_ARFLAGS := $(call ar-option,D)
>  include scripts/Makefile.kasan
>  include scripts/Makefile.extrawarn
>  include scripts/Makefile.ubsan
> +include scripts/Makefile.initmem
>
>  # Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
>  # last assignments
> diff --git a/scripts/Makefile.initmem b/scripts/Makefile.initmem
> new file mode 100644
> index 000000000000..a6253d78fe35
> --- /dev/null
> +++ b/scripts/Makefile.initmem
> @@ -0,0 +1,10 @@
> +ifdef CONFIG_INIT_ALL_STACK
> +
> +# Clang's -ftrivial-auto-var-init=pattern flag initializes the
> +# uninitialized parts of local variables (including fields and padding)
> +# with a fixed pattern (0xAA in most cases).
> +ifdef CONFIG_CC_HAS_AUTO_VAR_INIT
> +  CFLAGS_INITMEM := -ftrivial-auto-var-init=pattern
> +endif
> +
> +endif

Now that you dropped per-file control,
why is this necessary?
Also, CFLAGS_INITMEM is not wired up to anything,
so this patch has no effect.


I think you can add the following to top Makefile, and that's it.

ifdef CONFIG_AUTO_VAR_INIT
KBUILD_CFLAGS += -ftrivial-auto-var-init=pattern
endif




> diff --git a/security/Kconfig b/security/Kconfig
> index e4fe2f3c2c65..cc12a39424dd 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -230,6 +230,7 @@ config STATIC_USERMODEHELPER_PATH
>           If you wish for all usermode helper programs to be disabled,
>           specify an empty string here (i.e. "").
>
> +source "security/Kconfig.initmem"
>  source "security/selinux/Kconfig"
>  source "security/smack/Kconfig"
>  source "security/tomoyo/Kconfig"
> diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
> new file mode 100644
> index 000000000000..5e49a55382ad
> --- /dev/null
> +++ b/security/Kconfig.initmem
> @@ -0,0 +1,29 @@
> +menu "Initialize all memory"
> +
> +config CC_HAS_AUTO_VAR_INIT
> +       def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
> +
> +config INIT_ALL_MEMORY
> +       bool "Initialize all memory"
> +       default n
> +       help
> +         Enforce memory initialization to mitigate infoleaks and make
> +         the control-flow bugs depending on uninitialized values more
> +         deterministic.
> +
> +if INIT_ALL_MEMORY
> +
> +config INIT_ALL_STACK
> +       bool "Initialize all stack"
> +       depends on INIT_ALL_MEMORY
> +       depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
> +       select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
> +       select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
> +       select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
> +       default y
> +       help
> +         Initialize uninitialized stack data with a fixed pattern
> +         (0x00 in GCC, 0xAA in Clang).
> +


I am not sure about the benefit of these umbrella CONFIGs
since these make 'depends on' and 'select' complicated.
I will leave it to Kees, though.



> +endif # INIT_ALL_MEMORY
> +endmenu
> --
> 2.21.0.392.gf8f6787159e-goog
>
Alexander Potapenko April 9, 2019, 9:02 a.m. UTC | #4
On Tue, Apr 9, 2019 at 10:38 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> On Tue, Apr 9, 2019 at 2:04 AM Alexander Potapenko <glider@google.com> wrote:
> >
> > CONFIG_INIT_ALL_MEMORY is going to be an umbrella config for options
> > that force heap and stack initialization.
> > The rationale behind doing so is to reduce the severity of bugs caused
> > by using uninitialized memory.
> >
> > CONFIG_INIT_ALL_STACK turns on stack initialization based on
> > -ftrivial-auto-var-init in Clang builds and on
> > -fplugin-arg-structleak_plugin-byref-all in GCC builds.
> >
> > -ftrivial-auto-var-init is a Clang flag that provides trivial
> > initializers for uninitialized local variables, variable fields and
> > padding.
> >
> > It has three possible values:
> >   pattern - uninitialized locals are filled with a fixed pattern
> >     (mostly 0xAA on 64-bit platforms, see https://reviews.llvm.org/D54604
> >     for more details) likely to cause crashes when uninitialized value is
> >     used;
> >   zero (it's still debated whether this flag makes it to the official
> >     Clang release) - uninitialized locals are filled with zeroes;
> >   uninitialized (default) - uninitialized locals are left intact.
> >
> > The proposed config builds the kernel with
> > -ftrivial-auto-var-init=pattern.
> >
> > Developers have the possibility to opt-out of this feature on a
> > per-variable basis by using __attribute__((uninitialized)).
> >
> > For GCC builds, CONFIG_INIT_ALL_STACK is simply wired up to
> > CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. No opt-out is possible at the
> > moment.
> >
> > Signed-off-by: Alexander Potapenko <glider@google.com>
> > Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> > Cc: James Morris <jmorris@namei.org>
> > Cc: "Serge E. Hallyn" <serge@hallyn.com>
> > Cc: Nick Desaulniers <ndesaulniers@google.com>
> > Cc: Kostya Serebryany <kcc@google.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Sandeep Patil <sspatil@android.com>
> > Cc: linux-security-module@vger.kernel.org
> > Cc: linux-kbuild@vger.kernel.org
> > Cc: kernel-hardening@lists.openwall.com
> > ---
> >  v2:
> >   - addressed Kees Cook's comments: added GCC support
> >  v3: addressed Masahiro Yamada's comments:
> >   - dropped per-file opt-out mechanism
> >   - fixed GCC_PLUGINS dependencies
> > ---
> >  Makefile                 |  3 ++-
> >  scripts/Makefile.initmem | 10 ++++++++++
> >  security/Kconfig         |  1 +
> >  security/Kconfig.initmem | 29 +++++++++++++++++++++++++++++
> >  4 files changed, 42 insertions(+), 1 deletion(-)
> >  create mode 100644 scripts/Makefile.initmem
> >  create mode 100644 security/Kconfig.initmem
> >
> > diff --git a/Makefile b/Makefile
> > index f070e0d65186..028ca37878fd 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -448,7 +448,7 @@ export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
> >
> >  export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
> >  export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
> > -export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
> > +export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_INITMEM
> >  export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
> >  export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
> >  export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
> > @@ -840,6 +840,7 @@ KBUILD_ARFLAGS := $(call ar-option,D)
> >  include scripts/Makefile.kasan
> >  include scripts/Makefile.extrawarn
> >  include scripts/Makefile.ubsan
> > +include scripts/Makefile.initmem
> >
> >  # Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
> >  # last assignments
> > diff --git a/scripts/Makefile.initmem b/scripts/Makefile.initmem
> > new file mode 100644
> > index 000000000000..a6253d78fe35
> > --- /dev/null
> > +++ b/scripts/Makefile.initmem
> > @@ -0,0 +1,10 @@
> > +ifdef CONFIG_INIT_ALL_STACK
> > +
> > +# Clang's -ftrivial-auto-var-init=pattern flag initializes the
> > +# uninitialized parts of local variables (including fields and padding)
> > +# with a fixed pattern (0xAA in most cases).
> > +ifdef CONFIG_CC_HAS_AUTO_VAR_INIT
> > +  CFLAGS_INITMEM := -ftrivial-auto-var-init=pattern
> > +endif
> > +
> > +endif
>
> Now that you dropped per-file control,
> why is this necessary?
> Also, CFLAGS_INITMEM is not wired up to anything,
> so this patch has no effect.
There's CFLAGS_INITMEM in the top Makefile, so I suppose it should be working.
But I agree there's no point in adding extra files for a single build flag.
>
> I think you can add the following to top Makefile, and that's it.
>
> ifdef CONFIG_AUTO_VAR_INIT
> KBUILD_CFLAGS += -ftrivial-auto-var-init=pattern
> endif
>
>
>
>
> > diff --git a/security/Kconfig b/security/Kconfig
> > index e4fe2f3c2c65..cc12a39424dd 100644
> > --- a/security/Kconfig
> > +++ b/security/Kconfig
> > @@ -230,6 +230,7 @@ config STATIC_USERMODEHELPER_PATH
> >           If you wish for all usermode helper programs to be disabled,
> >           specify an empty string here (i.e. "").
> >
> > +source "security/Kconfig.initmem"
> >  source "security/selinux/Kconfig"
> >  source "security/smack/Kconfig"
> >  source "security/tomoyo/Kconfig"
> > diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
> > new file mode 100644
> > index 000000000000..5e49a55382ad
> > --- /dev/null
> > +++ b/security/Kconfig.initmem
> > @@ -0,0 +1,29 @@
> > +menu "Initialize all memory"
> > +
> > +config CC_HAS_AUTO_VAR_INIT
> > +       def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
> > +
> > +config INIT_ALL_MEMORY
> > +       bool "Initialize all memory"
> > +       default n
> > +       help
> > +         Enforce memory initialization to mitigate infoleaks and make
> > +         the control-flow bugs depending on uninitialized values more
> > +         deterministic.
> > +
> > +if INIT_ALL_MEMORY
> > +
> > +config INIT_ALL_STACK
> > +       bool "Initialize all stack"
> > +       depends on INIT_ALL_MEMORY
> > +       depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
> > +       select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
> > +       select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
> > +       select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
> > +       default y
> > +       help
> > +         Initialize uninitialized stack data with a fixed pattern
> > +         (0x00 in GCC, 0xAA in Clang).
> > +
>
>
> I am not sure about the benefit of these umbrella CONFIGs
> since these make 'depends on' and 'select' complicated.
> I will leave it to Kees, though.
>
>
>
> > +endif # INIT_ALL_MEMORY
> > +endmenu
> > --
> > 2.21.0.392.gf8f6787159e-goog
> >
>
>
> --
> Best Regards
> Masahiro Yamada
Alexander Potapenko April 9, 2019, 9:03 a.m. UTC | #5
On Tue, Apr 9, 2019 at 11:02 AM Alexander Potapenko <glider@google.com> wrote:
>
> On Tue, Apr 9, 2019 at 10:38 AM Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
> >
> > On Tue, Apr 9, 2019 at 2:04 AM Alexander Potapenko <glider@google.com> wrote:
> > >
> > > CONFIG_INIT_ALL_MEMORY is going to be an umbrella config for options
> > > that force heap and stack initialization.
> > > The rationale behind doing so is to reduce the severity of bugs caused
> > > by using uninitialized memory.
> > >
> > > CONFIG_INIT_ALL_STACK turns on stack initialization based on
> > > -ftrivial-auto-var-init in Clang builds and on
> > > -fplugin-arg-structleak_plugin-byref-all in GCC builds.
> > >
> > > -ftrivial-auto-var-init is a Clang flag that provides trivial
> > > initializers for uninitialized local variables, variable fields and
> > > padding.
> > >
> > > It has three possible values:
> > >   pattern - uninitialized locals are filled with a fixed pattern
> > >     (mostly 0xAA on 64-bit platforms, see https://reviews.llvm.org/D54604
> > >     for more details) likely to cause crashes when uninitialized value is
> > >     used;
> > >   zero (it's still debated whether this flag makes it to the official
> > >     Clang release) - uninitialized locals are filled with zeroes;
> > >   uninitialized (default) - uninitialized locals are left intact.
> > >
> > > The proposed config builds the kernel with
> > > -ftrivial-auto-var-init=pattern.
> > >
> > > Developers have the possibility to opt-out of this feature on a
> > > per-variable basis by using __attribute__((uninitialized)).
> > >
> > > For GCC builds, CONFIG_INIT_ALL_STACK is simply wired up to
> > > CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. No opt-out is possible at the
> > > moment.
> > >
> > > Signed-off-by: Alexander Potapenko <glider@google.com>
> > > Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> > > Cc: James Morris <jmorris@namei.org>
> > > Cc: "Serge E. Hallyn" <serge@hallyn.com>
> > > Cc: Nick Desaulniers <ndesaulniers@google.com>
> > > Cc: Kostya Serebryany <kcc@google.com>
> > > Cc: Dmitry Vyukov <dvyukov@google.com>
> > > Cc: Kees Cook <keescook@chromium.org>
> > > Cc: Sandeep Patil <sspatil@android.com>
> > > Cc: linux-security-module@vger.kernel.org
> > > Cc: linux-kbuild@vger.kernel.org
> > > Cc: kernel-hardening@lists.openwall.com
> > > ---
> > >  v2:
> > >   - addressed Kees Cook's comments: added GCC support
> > >  v3: addressed Masahiro Yamada's comments:
> > >   - dropped per-file opt-out mechanism
> > >   - fixed GCC_PLUGINS dependencies
> > > ---
> > >  Makefile                 |  3 ++-
> > >  scripts/Makefile.initmem | 10 ++++++++++
> > >  security/Kconfig         |  1 +
> > >  security/Kconfig.initmem | 29 +++++++++++++++++++++++++++++
> > >  4 files changed, 42 insertions(+), 1 deletion(-)
> > >  create mode 100644 scripts/Makefile.initmem
> > >  create mode 100644 security/Kconfig.initmem
> > >
> > > diff --git a/Makefile b/Makefile
> > > index f070e0d65186..028ca37878fd 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -448,7 +448,7 @@ export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
> > >
> > >  export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
> > >  export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
> > > -export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
> > > +export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_INITMEM
> > >  export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
> > >  export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
> > >  export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
> > > @@ -840,6 +840,7 @@ KBUILD_ARFLAGS := $(call ar-option,D)
> > >  include scripts/Makefile.kasan
> > >  include scripts/Makefile.extrawarn
> > >  include scripts/Makefile.ubsan
> > > +include scripts/Makefile.initmem
> > >
> > >  # Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
> > >  # last assignments
> > > diff --git a/scripts/Makefile.initmem b/scripts/Makefile.initmem
> > > new file mode 100644
> > > index 000000000000..a6253d78fe35
> > > --- /dev/null
> > > +++ b/scripts/Makefile.initmem
> > > @@ -0,0 +1,10 @@
> > > +ifdef CONFIG_INIT_ALL_STACK
> > > +
> > > +# Clang's -ftrivial-auto-var-init=pattern flag initializes the
> > > +# uninitialized parts of local variables (including fields and padding)
> > > +# with a fixed pattern (0xAA in most cases).
> > > +ifdef CONFIG_CC_HAS_AUTO_VAR_INIT
> > > +  CFLAGS_INITMEM := -ftrivial-auto-var-init=pattern
> > > +endif
> > > +
> > > +endif
> >
> > Now that you dropped per-file control,
> > why is this necessary?
> > Also, CFLAGS_INITMEM is not wired up to anything,
> > so this patch has no effect.
> There's CFLAGS_INITMEM in the top Makefile, so I suppose it should be working.
Ah, now I see. Yes, I was too hasty with this patchset.
> But I agree there's no point in adding extra files for a single build flag.
> >
> > I think you can add the following to top Makefile, and that's it.
> >
> > ifdef CONFIG_AUTO_VAR_INIT
> > KBUILD_CFLAGS += -ftrivial-auto-var-init=pattern
> > endif
> >
> >
> >
> >
> > > diff --git a/security/Kconfig b/security/Kconfig
> > > index e4fe2f3c2c65..cc12a39424dd 100644
> > > --- a/security/Kconfig
> > > +++ b/security/Kconfig
> > > @@ -230,6 +230,7 @@ config STATIC_USERMODEHELPER_PATH
> > >           If you wish for all usermode helper programs to be disabled,
> > >           specify an empty string here (i.e. "").
> > >
> > > +source "security/Kconfig.initmem"
> > >  source "security/selinux/Kconfig"
> > >  source "security/smack/Kconfig"
> > >  source "security/tomoyo/Kconfig"
> > > diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
> > > new file mode 100644
> > > index 000000000000..5e49a55382ad
> > > --- /dev/null
> > > +++ b/security/Kconfig.initmem
> > > @@ -0,0 +1,29 @@
> > > +menu "Initialize all memory"
> > > +
> > > +config CC_HAS_AUTO_VAR_INIT
> > > +       def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
> > > +
> > > +config INIT_ALL_MEMORY
> > > +       bool "Initialize all memory"
> > > +       default n
> > > +       help
> > > +         Enforce memory initialization to mitigate infoleaks and make
> > > +         the control-flow bugs depending on uninitialized values more
> > > +         deterministic.
> > > +
> > > +if INIT_ALL_MEMORY
> > > +
> > > +config INIT_ALL_STACK
> > > +       bool "Initialize all stack"
> > > +       depends on INIT_ALL_MEMORY
> > > +       depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
> > > +       select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
> > > +       select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
> > > +       select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
> > > +       default y
> > > +       help
> > > +         Initialize uninitialized stack data with a fixed pattern
> > > +         (0x00 in GCC, 0xAA in Clang).
> > > +
> >
> >
> > I am not sure about the benefit of these umbrella CONFIGs
> > since these make 'depends on' and 'select' complicated.
> > I will leave it to Kees, though.
> >
> >
> >
> > > +endif # INIT_ALL_MEMORY
> > > +endmenu
> > > --
> > > 2.21.0.392.gf8f6787159e-goog
> > >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
Kees Cook April 9, 2019, 5:06 p.m. UTC | #6
On Tue, Apr 9, 2019 at 1:38 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> > +config INIT_ALL_STACK
> > +       bool "Initialize all stack"
> > +       depends on INIT_ALL_MEMORY
> > +       depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
> > +       select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
> > +       select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
> > +       select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
> > +       default y
> > +       help
> > +         Initialize uninitialized stack data with a fixed pattern
> > +         (0x00 in GCC, 0xAA in Clang).
> > +
>
> I am not sure about the benefit of these umbrella CONFIGs
> since these make 'depends on' and 'select' complicated.
> I will leave it to Kees, though.

Yeah, I think this could use some more cleanup to get a single config
that represents that if gcc plugins are available (instead of having
it split across two configs now). Additionally I think this needs
refactoring against the current menu choices for
GCC_PLUGIN_STRUCTLEAK. Let me send a proposed patch in a few hours...

Patch
diff mbox series

diff --git a/Makefile b/Makefile
index f070e0d65186..028ca37878fd 100644
--- a/Makefile
+++ b/Makefile
@@ -448,7 +448,7 @@  export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
 export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
-export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_INITMEM
 export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
 export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
@@ -840,6 +840,7 @@  KBUILD_ARFLAGS := $(call ar-option,D)
 include scripts/Makefile.kasan
 include scripts/Makefile.extrawarn
 include scripts/Makefile.ubsan
+include scripts/Makefile.initmem
 
 # Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
 # last assignments
diff --git a/scripts/Makefile.initmem b/scripts/Makefile.initmem
new file mode 100644
index 000000000000..a6253d78fe35
--- /dev/null
+++ b/scripts/Makefile.initmem
@@ -0,0 +1,10 @@ 
+ifdef CONFIG_INIT_ALL_STACK
+
+# Clang's -ftrivial-auto-var-init=pattern flag initializes the
+# uninitialized parts of local variables (including fields and padding)
+# with a fixed pattern (0xAA in most cases).
+ifdef CONFIG_CC_HAS_AUTO_VAR_INIT
+  CFLAGS_INITMEM := -ftrivial-auto-var-init=pattern
+endif
+
+endif
diff --git a/security/Kconfig b/security/Kconfig
index e4fe2f3c2c65..cc12a39424dd 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -230,6 +230,7 @@  config STATIC_USERMODEHELPER_PATH
 	  If you wish for all usermode helper programs to be disabled,
 	  specify an empty string here (i.e. "").
 
+source "security/Kconfig.initmem"
 source "security/selinux/Kconfig"
 source "security/smack/Kconfig"
 source "security/tomoyo/Kconfig"
diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
new file mode 100644
index 000000000000..5e49a55382ad
--- /dev/null
+++ b/security/Kconfig.initmem
@@ -0,0 +1,29 @@ 
+menu "Initialize all memory"
+
+config CC_HAS_AUTO_VAR_INIT
+	def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
+
+config INIT_ALL_MEMORY
+	bool "Initialize all memory"
+	default n
+	help
+	  Enforce memory initialization to mitigate infoleaks and make
+	  the control-flow bugs depending on uninitialized values more
+	  deterministic.
+
+if INIT_ALL_MEMORY
+
+config INIT_ALL_STACK
+	bool "Initialize all stack"
+	depends on INIT_ALL_MEMORY
+	depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "")
+	select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT
+	select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT
+	select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT
+	default y
+	help
+	  Initialize uninitialized stack data with a fixed pattern
+	  (0x00 in GCC, 0xAA in Clang).
+
+endif # INIT_ALL_MEMORY
+endmenu