[2/3] Makefile: Move stackprotector availability out of Kconfig
diff mbox series

Message ID 1506972007-80614-3-git-send-email-keescook@chromium.org
State New, archived
Headers show
Series
  • Makefile: Introduce CONFIG_CC_STACKPROTECTOR_AUTO
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Commit Message

Kees Cook Oct. 2, 2017, 7:20 p.m. UTC
Various portions of the kernel, especially per-architecture pieces,
need to know if the compiler is building it with the stack protector.
This was done in the arch/Kconfig with 'select', but this doesn't
allow a way to do auto-detected compiler support. In preparation for
creating an on-if-available default, move the logic for the definition of
CONFIG_CC_STACKPROTECTOR into the Makefile.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <mmarek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 Makefile     | 7 +++++--
 arch/Kconfig | 8 --------
 2 files changed, 5 insertions(+), 10 deletions(-)

Comments

Masahiro Yamada Oct. 4, 2017, 2:33 p.m. UTC | #1
Hi Kees,


2017-10-03 4:20 GMT+09:00 Kees Cook <keescook@chromium.org>:
> Various portions of the kernel, especially per-architecture pieces,
> need to know if the compiler is building it with the stack protector.
> This was done in the arch/Kconfig with 'select', but this doesn't
> allow a way to do auto-detected compiler support. In preparation for
> creating an on-if-available default, move the logic for the definition of
> CONFIG_CC_STACKPROTECTOR into the Makefile.
>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Michal Marek <mmarek@suse.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Laura Abbott <labbott@redhat.com>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: linux-kbuild@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  Makefile     | 7 +++++--
>  arch/Kconfig | 8 --------
>  2 files changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index d1119941261c..e122a9cf0399 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -688,8 +688,11 @@ else
>    stackp-flag := $(call cc-option, -fno-stack-protector)
>  endif
>  endif
> -# Find arch-specific stack protector compiler sanity-checking script.
> -ifdef CONFIG_CC_STACKPROTECTOR
> +ifdef stackp-name
> +  # If the stack protector has been selected, inform the rest of the build.
> +  KBUILD_CFLAGS += -DCONFIG_CC_STACKPROTECTOR
> +  KBUILD_AFLAGS += -DCONFIG_CC_STACKPROTECTOR
> +  # Find arch-specific stack protector compiler sanity-checking script.
>    stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh
>    stackp-check := $(wildcard $(stackp-path))
>  endif


I have not tested this series,
but I think this commit is bad (with the follow-up patch applied).


I thought of this scenario:

[1] Kernel is configured with CONFIG_CC_STACKPROTECTOR_AUTO

[2] Kernel is built with a compiler without stack protector support.

[3] CONFIG_CC_STACKPROTECTOR is not defined,
    so __stack_chk_fail() is not compiled.

[4] Out-of-tree modules are compiled with a compiler with
    stack protector support.
    __stack_chk_fail() is inserted to functions of the modules.

[5] insmod fails because reference to __stack_chk_fail()
    can not be resolved.




I think "select CC_STACKPROTECTOR" should be kept in Kconfig.
Greg KH Oct. 4, 2017, 3:13 p.m. UTC | #2
On Wed, Oct 04, 2017 at 11:33:38PM +0900, Masahiro Yamada wrote:
> Hi Kees,
> 
> 
> 2017-10-03 4:20 GMT+09:00 Kees Cook <keescook@chromium.org>:
> > Various portions of the kernel, especially per-architecture pieces,
> > need to know if the compiler is building it with the stack protector.
> > This was done in the arch/Kconfig with 'select', but this doesn't
> > allow a way to do auto-detected compiler support. In preparation for
> > creating an on-if-available default, move the logic for the definition of
> > CONFIG_CC_STACKPROTECTOR into the Makefile.
> >
> > Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> > Cc: Michal Marek <mmarek@suse.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Laura Abbott <labbott@redhat.com>
> > Cc: Nicholas Piggin <npiggin@gmail.com>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: linux-kbuild@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  Makefile     | 7 +++++--
> >  arch/Kconfig | 8 --------
> >  2 files changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index d1119941261c..e122a9cf0399 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -688,8 +688,11 @@ else
> >    stackp-flag := $(call cc-option, -fno-stack-protector)
> >  endif
> >  endif
> > -# Find arch-specific stack protector compiler sanity-checking script.
> > -ifdef CONFIG_CC_STACKPROTECTOR
> > +ifdef stackp-name
> > +  # If the stack protector has been selected, inform the rest of the build.
> > +  KBUILD_CFLAGS += -DCONFIG_CC_STACKPROTECTOR
> > +  KBUILD_AFLAGS += -DCONFIG_CC_STACKPROTECTOR
> > +  # Find arch-specific stack protector compiler sanity-checking script.
> >    stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh
> >    stackp-check := $(wildcard $(stackp-path))
> >  endif
> 
> 
> I have not tested this series,
> but I think this commit is bad (with the follow-up patch applied).
> 
> 
> I thought of this scenario:
> 
> [1] Kernel is configured with CONFIG_CC_STACKPROTECTOR_AUTO
> 
> [2] Kernel is built with a compiler without stack protector support.
> 
> [3] CONFIG_CC_STACKPROTECTOR is not defined,
>     so __stack_chk_fail() is not compiled.
> 
> [4] Out-of-tree modules are compiled with a compiler with
>     stack protector support.
>     __stack_chk_fail() is inserted to functions of the modules.

We don't ever support the system of loading a module built with anything
other than the _exact_ same compiler than the kernel was.  So this will
not happen (well, if someone tries it, they get to keep the pieces their
kernel image is now in...)

> [5] insmod fails because reference to __stack_chk_fail()
>     can not be resolved.

Even nicer, we failed "cleanly" :)

This isn't a real-world issue, sorry.

thanks,

greg k-h
Kees Cook Oct. 4, 2017, 4:22 p.m. UTC | #3
On Wed, Oct 4, 2017 at 8:13 AM, Greg KH <greg@kroah.com> wrote:
> On Wed, Oct 04, 2017 at 11:33:38PM +0900, Masahiro Yamada wrote:
>> Hi Kees,
>>
>>
>> 2017-10-03 4:20 GMT+09:00 Kees Cook <keescook@chromium.org>:
>> > Various portions of the kernel, especially per-architecture pieces,
>> > need to know if the compiler is building it with the stack protector.
>> > This was done in the arch/Kconfig with 'select', but this doesn't
>> > allow a way to do auto-detected compiler support. In preparation for
>> > creating an on-if-available default, move the logic for the definition of
>> > CONFIG_CC_STACKPROTECTOR into the Makefile.
>> >
>> > Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
>> > Cc: Michal Marek <mmarek@suse.com>
>> > Cc: Andrew Morton <akpm@linux-foundation.org>
>> > Cc: Ingo Molnar <mingo@kernel.org>
>> > Cc: Laura Abbott <labbott@redhat.com>
>> > Cc: Nicholas Piggin <npiggin@gmail.com>
>> > Cc: Al Viro <viro@zeniv.linux.org.uk>
>> > Cc: linux-kbuild@vger.kernel.org
>> > Signed-off-by: Kees Cook <keescook@chromium.org>
>> > ---
>> >  Makefile     | 7 +++++--
>> >  arch/Kconfig | 8 --------
>> >  2 files changed, 5 insertions(+), 10 deletions(-)
>> >
>> > diff --git a/Makefile b/Makefile
>> > index d1119941261c..e122a9cf0399 100644
>> > --- a/Makefile
>> > +++ b/Makefile
>> > @@ -688,8 +688,11 @@ else
>> >    stackp-flag := $(call cc-option, -fno-stack-protector)
>> >  endif
>> >  endif
>> > -# Find arch-specific stack protector compiler sanity-checking script.
>> > -ifdef CONFIG_CC_STACKPROTECTOR
>> > +ifdef stackp-name
>> > +  # If the stack protector has been selected, inform the rest of the build.
>> > +  KBUILD_CFLAGS += -DCONFIG_CC_STACKPROTECTOR
>> > +  KBUILD_AFLAGS += -DCONFIG_CC_STACKPROTECTOR
>> > +  # Find arch-specific stack protector compiler sanity-checking script.
>> >    stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh
>> >    stackp-check := $(wildcard $(stackp-path))
>> >  endif
>>
>>
>> I have not tested this series,
>> but I think this commit is bad (with the follow-up patch applied).
>>
>>
>> I thought of this scenario:
>>
>> [1] Kernel is configured with CONFIG_CC_STACKPROTECTOR_AUTO
>>
>> [2] Kernel is built with a compiler without stack protector support.
>>
>> [3] CONFIG_CC_STACKPROTECTOR is not defined,
>>     so __stack_chk_fail() is not compiled.
>>
>> [4] Out-of-tree modules are compiled with a compiler with
>>     stack protector support.
>>     __stack_chk_fail() is inserted to functions of the modules.
>
> We don't ever support the system of loading a module built with anything
> other than the _exact_ same compiler than the kernel was.  So this will
> not happen (well, if someone tries it, they get to keep the pieces their
> kernel image is now in...)
>
>> [5] insmod fails because reference to __stack_chk_fail()
>>     can not be resolved.
>
> Even nicer, we failed "cleanly" :)
>
> This isn't a real-world issue, sorry.

If we wanted a slightly different failure, we could simply add the
stack protection feature to the VERMAGIC_STRING define:

diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index af6c03f7f986..300163aba666 100644
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h
@@ -30,11 +30,19 @@
 #else
 #define MODULE_RANDSTRUCT_PLUGIN
 #endif
+#if defined(__SSP__)
+#define MODULE_STACKPROTECTOR "stack-protector "
+#elif define (__SSP_STRONG__)
+#define MODULE_STACKPROTECTOR "stack-protector-strong "
+#else
+#define MODULE_STACKPROTECTOR ""
+#endif

 #define VERMAGIC_STRING                                                \
        UTS_RELEASE " "                                                 \
        MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT                     \
        MODULE_VERMAGIC_MODULE_UNLOAD MODULE_VERMAGIC_MODVERSIONS       \
        MODULE_ARCH_VERMAGIC                                            \
+       MODULE_STACKPROTECTOR                                           \
        MODULE_RANDSTRUCT_PLUGIN


Do you want me to send this patch, or should we allow it to fail with
the "missing reference" (which may actually be more expressive...) I
think the way it is right now is better, but I'm open to either.

-Kees
Greg KH Oct. 4, 2017, 5:15 p.m. UTC | #4
On Wed, Oct 04, 2017 at 09:22:24AM -0700, Kees Cook wrote:
> Do you want me to send this patch, or should we allow it to fail with
> the "missing reference" (which may actually be more expressive...) I
> think the way it is right now is better, but I'm open to either.

I think the current way is fine.

And nice work on the patchset.

greg k-h

Patch
diff mbox series

diff --git a/Makefile b/Makefile
index d1119941261c..e122a9cf0399 100644
--- a/Makefile
+++ b/Makefile
@@ -688,8 +688,11 @@  else
   stackp-flag := $(call cc-option, -fno-stack-protector)
 endif
 endif
-# Find arch-specific stack protector compiler sanity-checking script.
-ifdef CONFIG_CC_STACKPROTECTOR
+ifdef stackp-name
+  # If the stack protector has been selected, inform the rest of the build.
+  KBUILD_CFLAGS += -DCONFIG_CC_STACKPROTECTOR
+  KBUILD_AFLAGS += -DCONFIG_CC_STACKPROTECTOR
+  # Find arch-specific stack protector compiler sanity-checking script.
   stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh
   stackp-check := $(wildcard $(stackp-path))
 endif
diff --git a/arch/Kconfig b/arch/Kconfig
index 1aafb4efbb51..7007c1bfa79c 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -523,12 +523,6 @@  config HAVE_CC_STACKPROTECTOR
 	  - its compiler supports the -fstack-protector option
 	  - it has implemented a stack canary (e.g. __stack_chk_guard)
 
-config CC_STACKPROTECTOR
-	def_bool n
-	help
-	  Set when a stack-protector mode is enabled, so that the build
-	  can enable kernel-side support for the GCC feature.
-
 choice
 	prompt "Stack Protector buffer overflow detection"
 	depends on HAVE_CC_STACKPROTECTOR
@@ -549,7 +543,6 @@  config CC_STACKPROTECTOR_NONE
 
 config CC_STACKPROTECTOR_REGULAR
 	bool "Regular"
-	select CC_STACKPROTECTOR
 	help
 	  Functions will have the stack-protector canary logic added if they
 	  have an 8-byte or larger character array on the stack.
@@ -563,7 +556,6 @@  config CC_STACKPROTECTOR_REGULAR
 
 config CC_STACKPROTECTOR_STRONG
 	bool "Strong"
-	select CC_STACKPROTECTOR
 	help
 	  Functions will have the stack-protector canary logic added in any
 	  of the following conditions: