From: Peter Collingbourne <pcc@xxxxxxxxxx>
Subject: kasan: fix kasan_byte_accessible() to be consistent with actual checks
We can sometimes end up with kasan_byte_accessible() being called on
non-slab memory. For example ksize() and krealloc() may end up calling it
on KFENCE allocated memory. In this case the memory will be tagged with
KASAN_SHADOW_INIT, which a subsequent patch ("kasan: initialize shadow to
TAG_INVALID for SW_TAGS") will set to the same value as KASAN_TAG_INVALID,
causing kasan_byte_accessible() to fail when called on non-slab memory.
This highlighted the fact that the check in kasan_byte_accessible() was
inconsistent with checks as implemented for loads and stores
(kasan_check_range() in SW tags mode and hardware-implemented checks in HW
tags mode). kasan_check_range() does not have a check for
KASAN_TAG_INVALID, and instead has a comparison against
KASAN_SHADOW_START. In HW tags mode, we do not have either, but we do set
TCR_EL1.TCMA which corresponds with the comparison against
KASAN_TAG_KERNEL.
Therefore, update kasan_byte_accessible() for both SW and HW tags modes to
correspond with the respective checks on loads and stores.
Link: https://linux-review.googlesource.com/id/Ic6d40803c57dcc6331bd97fbb9a60b0d38a65a36
Link: https://lkml.kernel.org/r/20210405220647.1965262-1-pcc@xxxxxxxxxx
Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kasan/kasan.h | 3 +--
mm/kasan/sw_tags.c | 10 +++++++---
2 files changed, 8 insertions(+), 5 deletions(-)
--- a/mm/kasan/kasan.h~kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks
+++ a/mm/kasan/kasan.h
@@ -396,8 +396,7 @@ static inline bool kasan_byte_accessible
u8 ptr_tag = get_tag(addr);
u8 mem_tag = hw_get_mem_tag((void *)addr);
- return (mem_tag != KASAN_TAG_INVALID) &&
- (ptr_tag == KASAN_TAG_KERNEL || ptr_tag == mem_tag);
+ return ptr_tag == KASAN_TAG_KERNEL || ptr_tag == mem_tag;
}
#else /* CONFIG_KASAN_HW_TAGS */
--- a/mm/kasan/sw_tags.c~kasan-fix-kasan_byte_accessible-to-be-consistent-with-actual-checks
+++ a/mm/kasan/sw_tags.c
@@ -121,10 +121,14 @@ bool kasan_check_range(unsigned long add
bool kasan_byte_accessible(const void *addr)
{
u8 tag = get_tag(addr);
- u8 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(kasan_reset_tag(addr)));
+ void *untagged_addr = kasan_reset_tag(addr);
+ u8 shadow_byte;
- return (shadow_byte != KASAN_TAG_INVALID) &&
- (tag == KASAN_TAG_KERNEL || tag == shadow_byte);
+ if (untagged_addr < kasan_shadow_to_mem((void *)KASAN_SHADOW_START))
+ return false;
+
+ shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(untagged_addr));
+ return tag == KASAN_TAG_KERNEL || tag == shadow_byte;
}
#define DEFINE_HWASAN_LOAD_STORE(size) \
_
