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
Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
---
mm/kasan/kasan.h | 3 +--
mm/kasan/sw_tags.c | 10 +++++++---
2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 8c55634d6edd..e18e8da35255 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -368,8 +368,7 @@ static inline bool kasan_byte_accessible(const void *addr)
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 */
diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
index 94c2d33be333..00ae8913fc74 100644
--- a/mm/kasan/sw_tags.c
+++ b/mm/kasan/sw_tags.c
@@ -121,10 +121,14 @@ bool kasan_check_range(unsigned long addr, size_t size, bool write,
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) \
--
2.31.0.208.g409f899ff0-goog
