[PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[Arnd Bergmann]

In the upcoming gcc-7 release, the -fsanitize=kernel-address option
implies -fsanitize-address-use-after-scope, which relies on the
definition of two global functions, causing many link errors if they
are not defined, e.g:

arch/x86/built-in.o: In function `x86_pmu_handle_irq':
(.text+0x88e6): undefined reference to `__asan_unpoison_stack_memory'
arch/x86/built-in.o: In function `x86_pmu_handle_irq':
(.text+0x8ad7): undefined reference to `__asan_poison_stack_memory'
kernel/built-in.o: In function `perf_tp_event':
(.text+0x225472): undefined reference to `__asan_unpoison_stack_memory'
kernel/built-in.o: In function `perf_tp_event':
(.text+0x22583a): undefined reference to `__asan_unpoison_stack_memory'
kernel/built-in.o: In function `perf_tp_event':
(.text+0x2258ae): undefined reference to `__asan_poison_stack_memory'
kernel/built-in.o: In function `perf_event_aux_event':

I think we really want to define those two functions so we can make
use of a helpful feature, but as I have no idea what they are supposed
to do, I'd suggest to turn the option off on existing kernels to allow
building with gcc-7 and kasan.

For some reason, the problem showed up in only a few randconfig builds,
but it is easy to reproduce using an x86-64 tinyconfig build with
CONFIG_KASAN=y.

If we decide to take this approach, we probably want to do the same
change on all stable kernels that support KASAN, i.e. v4.0 or higher.

Link: https://gcc.gnu.org/viewcvs/gcc?limit_changes=0&view=revision&revision=241896
Cc: Martin Liška <marxin@gcc.gnu.org>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 scripts/Makefile.kasan | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 37323b0df374..0e68fef09f76 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -29,3 +29,5 @@ else
     endif
 endif
 endif
+
+CFLAGS_KASAN += $(call cc-option, -fno-sanitize-address-use-after-scope)
-- 
2.9.0

Re: [PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[Andrey Ryabinin]

On 11/23/2016 01:54 AM, Arnd Bergmann wrote:
> In the upcoming gcc-7 release, the -fsanitize=kernel-address option
> implies -fsanitize-address-use-after-scope, which relies on the
> definition of two global functions, causing many link errors if they
> are not defined, e.g:
> 
> arch/x86/built-in.o: In function `x86_pmu_handle_irq':
> (.text+0x88e6): undefined reference to `__asan_unpoison_stack_memory'
> arch/x86/built-in.o: In function `x86_pmu_handle_irq':
> (.text+0x8ad7): undefined reference to `__asan_poison_stack_memory'
> kernel/built-in.o: In function `perf_tp_event':
> (.text+0x225472): undefined reference to `__asan_unpoison_stack_memory'
> kernel/built-in.o: In function `perf_tp_event':
> (.text+0x22583a): undefined reference to `__asan_unpoison_stack_memory'
> kernel/built-in.o: In function `perf_tp_event':
> (.text+0x2258ae): undefined reference to `__asan_poison_stack_memory'
> kernel/built-in.o: In function `perf_event_aux_event':
> 
> I think we really want to define those two functions so we can make
> use of a helpful feature, but as I have no idea what they are supposed
> to do, I'd suggest to turn the option off on existing kernels to allow
> building with gcc-7 and kasan.
> 
> For some reason, the problem showed up in only a few randconfig builds,
> but it is easy to reproduce using an x86-64 tinyconfig build with
> CONFIG_KASAN=y.
> 
> If we decide to take this approach, we probably want to do the same
> change on all stable kernels that support KASAN, i.e. v4.0 or higher.
> 

We have implementation for this feature:
	"[PATCH] kasan: support use-after-scope detection" - http://lkml.kernel.org/r/<1479226045-145148-1-git-send-email-dvyukov@google.com>
and given how simple it is I'd suggest to just backport implementation.

BTW, we also need "[PATCH] kasan: update kasan_global for gcc 7" - http://lkml.kernel.org/r/<1479219743-28682-1-git-send-email-dvyukov@google.com>
in v4.0+ stable.

> Link: https://gcc.gnu.org/viewcvs/gcc?limit_changes=0&view=revision&revision=241896
> Cc: Martin Liška <marxin@gcc.gnu.org>
> Cc: Andrey Ryabinin <a.ryabinin@samsung.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  scripts/Makefile.kasan | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 37323b0df374..0e68fef09f76 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -29,3 +29,5 @@ else
>      endif
>  endif
>  endif
> +
> +CFLAGS_KASAN += $(call cc-option, -fno-sanitize-address-use-after-scope)
> 

Re: [PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[Arnd Bergmann]

On Wednesday, November 23, 2016 11:25:49 AM CET Andrey Ryabinin wrote:
> 
> We have implementation for this feature:
>         "[PATCH] kasan: support use-after-scope detection" - http://lkml.kernel.org/r/<1479226045-145148-1-git-send-email-dvyukov@google.com>
> and given how simple it is I'd suggest to just backport implementation.
> 
> BTW, we also need "[PATCH] kasan: update kasan_global for gcc 7" - http://lkml.kernel.org/r/<1479219743-28682-1-git-send-email-dvyukov@google.com>
> in v4.0+ stable.

Ah, good. What's the plan for this patch? Would you still expect to
see that merged into v4.9, or get backported later once it's part of v4.10?

Either way, you proabably want a Cc:stable tag on it to trigger the
backport to older kernels.

	Arnd

Re: [PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[Dmitry Vyukov]

On Wed, Nov 23, 2016 at 9:46 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday, November 23, 2016 11:25:49 AM CET Andrey Ryabinin wrote:
>>
>> We have implementation for this feature:
>>         "[PATCH] kasan: support use-after-scope detection" - http://lkml.kernel.org/r/<1479226045-145148-1-git-send-email-dvyukov@google.com>
>> and given how simple it is I'd suggest to just backport implementation.
>>
>> BTW, we also need "[PATCH] kasan: update kasan_global for gcc 7" - http://lkml.kernel.org/r/<1479219743-28682-1-git-send-email-dvyukov@google.com>
>> in v4.0+ stable.
>
> Ah, good. What's the plan for this patch? Would you still expect to
> see that merged into v4.9, or get backported later once it's part of v4.10?
>
> Either way, you proabably want a Cc:stable tag on it to trigger the
> backport to older kernels.

+Andrew, what is the plan for the "[PATCH] kasan: update kasan_global
for gcc 7" patch?
Do I need to remail to include Cc:stable?

Re: [PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[Andrew Morton]

On Wed, 23 Nov 2016 10:33:41 +0100 Dmitry Vyukov <dvyukov@google.com> wrote:

> On Wed, Nov 23, 2016 at 9:46 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wednesday, November 23, 2016 11:25:49 AM CET Andrey Ryabinin wrote:
> >>
> >> We have implementation for this feature:
> >>         "[PATCH] kasan: support use-after-scope detection" - http://lkml.kernel.org/r/<1479226045-145148-1-git-send-email-dvyukov@google.com>
> >> and given how simple it is I'd suggest to just backport implementation.
> >>
> >> BTW, we also need "[PATCH] kasan: update kasan_global for gcc 7" - http://lkml.kernel.org/r/<1479219743-28682-1-git-send-email-dvyukov@google.com>
> >> in v4.0+ stable.
> >
> > Ah, good. What's the plan for this patch? Would you still expect to
> > see that merged into v4.9, or get backported later once it's part of v4.10?
> >
> > Either way, you proabably want a Cc:stable tag on it to trigger the
> > backport to older kernels.
> 
> +Andrew, what is the plan for the "[PATCH] kasan: update kasan_global
> for gcc 7" patch?
> Do I need to remail to include Cc:stable?

I'm planning on merging it into 4.10-rc1.  There's nothing in the
changelog to indicate that it is more urgent than that.

Please send out a new changelog which can be used to justify a merge
into 4.9 and -stable.

Re: [PATCH] kasan: turn off -fsanitize-address-use-after-scope for now

[Dmitry Vyukov]

On Wed, Nov 23, 2016 at 7:49 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Wed, 23 Nov 2016 10:33:41 +0100 Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> On Wed, Nov 23, 2016 at 9:46 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>> > On Wednesday, November 23, 2016 11:25:49 AM CET Andrey Ryabinin wrote:
>> >>
>> >> We have implementation for this feature:
>> >>         "[PATCH] kasan: support use-after-scope detection" - http://lkml.kernel.org/r/<1479226045-145148-1-git-send-email-dvyukov@google.com>
>> >> and given how simple it is I'd suggest to just backport implementation.
>> >>
>> >> BTW, we also need "[PATCH] kasan: update kasan_global for gcc 7" - http://lkml.kernel.org/r/<1479219743-28682-1-git-send-email-dvyukov@google.com>
>> >> in v4.0+ stable.
>> >
>> > Ah, good. What's the plan for this patch? Would you still expect to
>> > see that merged into v4.9, or get backported later once it's part of v4.10?
>> >
>> > Either way, you proabably want a Cc:stable tag on it to trigger the
>> > backport to older kernels.
>>
>> +Andrew, what is the plan for the "[PATCH] kasan: update kasan_global
>> for gcc 7" patch?
>> Do I need to remail to include Cc:stable?
>
> I'm planning on merging it into 4.10-rc1.  There's nothing in the
> changelog to indicate that it is more urgent than that.
>
> Please send out a new changelog which can be used to justify a merge
> into 4.9 and -stable.

Remailed the patches with Cc: stable@vger.kernel.org # 4.0+
and with a note that without these patches KASAN is broken with gcc 7.