[tip: x86/core] x86: Suppress KMSAN reports in arch_within_stack_frames()

[tip-bot2 for Alexander Potapenko]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     ce3ba2af9695e4bd64d797e0026321e5dca29dd3
Gitweb:        https://git.kernel.org/tip/ce3ba2af9695e4bd64d797e0026321e5dca29dd3
Author:        Alexander Potapenko <glider@xxxxxxxxxx>
AuthorDate:    Fri, 18 Nov 2022 18:23:05 +01:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Fri, 27 Jan 2023 09:00:56 -08:00

x86: Suppress KMSAN reports in arch_within_stack_frames()

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.

Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Tested-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Link: https://github.com/google/kmsan/issues/89
Link: https://lore.kernel.org/lkml/Y3b9AAEKp2Vr3e6O@sol.localdomain/
Link: https://lore.kernel.org/all/20221118172305.3321253-1-glider%40google.com
---
 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 f0cb881..f1cccba 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)