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ANDROID: kasan: fix interoperability with KFENCE

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MTE-related KASAN changes were preceded by noticeable KASAN refactorings
that were backported to android12-5.10, but not android12-5.4.
As a result, some last-minute mm changes fixing "kfence, kasan: make KFENCE
compatible with KASAN"
(https://android.googlesource.com/kernel/common/+/f03825db4d6834a9d97e96eee2404a36ca79dafa)
did not make it to android12-5.4.

Given that they do not exist as separate upstream commits and do not
apply cleanly to 5.4 kernels, reimplement them.

These changes boil down to skipping KASAN poisoning for KFENCE-allocated
objects and to resetting the object tag in __kasan_kmalloc().

Bug: 172318110
Bug: 190593700
Signed-off-by: Alexander Potapenko <glider@google.com>
Change-Id: I117ea37a1d41514a3c5beaf87386bb5f2f0046c8
This commit is contained in:
Alexander Potapenko 2021-06-09 14:05:25 +02:00 • committed by Michael Bestas
commit 9484ee8820
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1 changed files with 13 additions and 1 deletions
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14
mm/kasan/common.c
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@ -141,6 +141,10 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
*/
address = reset_tag(address);
/* Skip KFENCE memory if called explicitly outside of sl*b. */
if (is_kfence_address(address))
return;
shadow_start = kasan_mem_to_shadow(address);
shadow_end = kasan_mem_to_shadow(address + size);
@ -158,6 +162,14 @@ void kasan_unpoison_shadow(const void *address, size_t size)
*/
address = reset_tag(address);
/*
* Skip KFENCE memory if called explicitly outside of sl*b. Also note
* that calls to ksize(), where size is not a multiple of machine-word
* size, would otherwise poison the invalid portion of the word.
*/
if (is_kfence_address(address))
return;
kasan_poison_shadow(address, size, tag);
if (size & KASAN_SHADOW_MASK) {
@ -497,7 +509,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
if (unlikely(object == NULL))
return NULL;
if (is_kfence_address(object))
if (is_kfence_address(kasan_reset_tag(object)))
return (void *)object;
redzone_start = round_up((unsigned long)(object + size),