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

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

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)
>