[PATCH] x86_64: increase stack size for KASAN_EXTRA

[Qian Cai]

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 <cai@xxxxxx>
---
 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
+#else
 #define KASAN_STACK_ORDER 1
+#endif
 #else
 #define KASAN_STACK_ORDER 0
 #endif
-- 
2.17.2 (Apple Git-113)