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@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Eric Biggers <ebiggers@google.com>
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

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index f0cb881..f1cccba 100644 (file)
--- 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)