Re: Patch "x86_64: increase stack size for KASAN_EXTRA" has been added to the 4.20-stable tree

Greg KH
2019-02-21T11:46:12Z

On Thu, Feb 21, 2019 at 12:43:23AM -0500, Sasha Levin wrote:
> This is a note to let you know that I've just added the patch titled
>
> x86_64: increase stack size for KASAN_EXTRA
>
> to the 4.20-stable tree which can be found at:
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
> x86_64-increase-stack-size-for-kasan_extra.patch
> and it can be found in the queue-4.20 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
>
>
>
> commit 67fd2fd35761d6bb8dcebe5070960c2f0baaef69
> Author: Qian Cai <cai@lca.pw>
> Date: Fri Feb 1 14:20:20 2019 -0800
>
> x86_64: increase stack size for KASAN_EXTRA
>
> [ Upstream commit a8e911d13540487942d53137c156bd7707f66e5d ]
>
> If the kernel is configured with KASAN_EXTRA, the stack size is
> increasted significantly because this option sets "-fstack-reuse" to
> "none" in GCC [1]. As a result, it triggers stack overrun quite often
> with 32k stack size compiled using GCC 8. For example, this reproducer
>
> https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise06.c
>
> triggers a "corrupted stack end detected inside scheduler" very reliably
> with CONFIG_SCHED_STACK_END_CHECK enabled.
>
> There are just too many functions that could have a large stack with
> KASAN_EXTRA due to large local variables that have been called over and
> over again without being able to reuse the stacks. Some noticiable ones
> are
>
> size
> 7648 shrink_page_list
> 3584 xfs_rmap_convert
> 3312 migrate_page_move_mapping
> 3312 dev_ethtool
> 3200 migrate_misplaced_transhuge_page
> 3168 copy_process
>
> There are other 49 functions are over 2k in size while compiling kernel
> with "-Wframe-larger-than=" even with a related minimal config on this
> machine. Hence, it is too much work to change Makefiles for each object
> to compile without "-fsanitize-address-use-after-scope" individually.
>
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715#c23
>
> Although there is a patch in GCC 9 to help the situation, GCC 9 probably
> won't be released in a few months and then it probably take another
> 6-month to 1-year for all major distros to include it as a default.
> Hence, the stack usage with KASAN_EXTRA can be revisited again in 2020
> when GCC 9 is everywhere. Until then, this patch will help users avoid
> stack overrun.
>
> This has already been fixed for arm64 for the same reason via
> 6e8830674ea ("arm64: kasan: Increase stack size for KASAN_EXTRA").
>
> Link: http://lkml.kernel.org/r/20190109215209.2903-1-cai@lca.pw
> Signed-off-by: Qian Cai <cai@lca.pw>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
>
> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> index 8f657286d599a..0ce558a8150d3 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/arch/x86/include/asm/page_64_types.h
> @@ -7,7 +7,11 @@
> #endif
>
> #ifdef CONFIG_KASAN
> +#ifdef CONFIG_KASAN_EXTRA
> +#define KASAN_STACK_ORDER 2
> +#else
> #define KASAN_STACK_ORDER 1
> +#endif
> #else
> #define KASAN_STACK_ORDER 0
> #endif

This looks like it is also relevant for 4.19.y so I have queued it up
there too.

greg k-h