Even though the KMSAN warnings generated by memchr_inv() are suppressed by metadata_access_enable(), its return value may still be poisoned. The reason is that the last iteration of memchr_inv() returns `*start != value ? start : NULL`, where *start is poisoned. Because of this, somewhat counterintuitively, the shadow value computed by visitSelectInst() is equal to `(uintptr_t)start`. The intention behind guarding memchr_inv() behind metadata_access_enable() is to touch poisoned metadata without triggering KMSAN, so unpoison its return value. Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx> --- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index a290f6c63e7b..b9101b2dc9aa 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1185,6 +1185,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct slab *slab, metadata_access_enable(); fault = memchr_inv(kasan_reset_tag(start), value, bytes); metadata_access_disable(); + kmsan_unpoison_memory(&fault, sizeof(fault)); if (!fault) return 1; @@ -1291,6 +1292,7 @@ static void slab_pad_check(struct kmem_cache *s, struct slab *slab) metadata_access_enable(); fault = memchr_inv(kasan_reset_tag(pad), POISON_INUSE, remainder); metadata_access_disable(); + kmsan_unpoison_memory(&fault, sizeof(fault)); if (!fault) return; while (end > fault && end[-1] == POISON_INUSE) -- 2.45.1
