[PATCH] x86: suppress KMSAN reports in arch_within_stack_frames()

[Alexander Potapenko]

arch_within_stack_frames() performs stack walking and may confuse
KMSAN by stepping on stale shadow values. To prevent false positive
reports, disable KMSAN checks in this function.

This fixes KMSAN's interoperability with CONFIG_HARDENED_USERCOPY.

Link: https://github.com/google/kmsan/issues/89
Link: https://lore.kernel.org/lkml/Y3b9AAEKp2Vr3e6O@sol.localdomain/
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
 arch/x86/include/asm/thread_info.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index f0cb881c1d690..f1cccba52eb97 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -163,7 +163,12 @@ struct thread_info {
  *	GOOD_FRAME	if within a frame
  *	BAD_STACK	if placed across a frame boundary (or outside stack)
  *	NOT_STACK	unable to determine (no frame pointers, etc)
+ *
+ * This function reads pointers from the stack and dereferences them. The
+ * pointers may not have their KMSAN shadow set up properly, which may result
+ * in false positive reports. Disable instrumentation to avoid those.
  */
+__no_kmsan_checks
 static inline int arch_within_stack_frames(const void * const stack,
 					   const void * const stackend,
 					   const void *obj, unsigned long len)
-- 
2.38.1.584.g0f3c55d4c2-goog