On 1/10/19 12:52 AM, Qian Cai wrote: > If the kernel is configured with KASAN_EXTRA, the stack size is > increasted significantly due to enable this option will set > "-fstack-reuse" to "none" in GCC [1]. As the results, it could trigger > 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 > > could trigger 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). > > Signed-off-by: Qian Cai <c...@lca.pw> > --- > arch/x86/include/asm/page_64_types.h | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/include/asm/page_64_types.h > b/arch/x86/include/asm/page_64_types.h > index 8f657286d599..0ce558a8150d 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 So the kernel stack becomes 4-order page. That's above PAGE_ALLOC_COSTLY_ORDER, so people will start seeing fork() failures with -ENOMEM due to high memory fragmentation. I don't think we can afford such change. Give that use-after-scope has proven to be almost useless for the kernel, I think we should just remove it entirely. > +#else > #define KASAN_STACK_ORDER 1 > +#endif > #else > #define KASAN_STACK_ORDER 0 > #endif >