Re: [PATCH v3 15/34] mm: slub: Unpoison the memchr_inv() return value
From: Vlastimil Babka <hidden>
Date: 2024-01-02 16:10:55
Also in:
linux-mm, linux-s390, lkml
On 12/14/23 00:24, Ilya Leoshkevich wrote:
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. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Vlastimil Babka <redacted>
quoted hunk ↗ jump to hunk
--- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+)diff --git a/mm/slub.c b/mm/slub.c index 2d29d368894c..802702748925 100644 --- a/mm/slub.c +++ b/mm/slub.c@@ -1076,6 +1076,7 @@ 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;@@ -1182,6 +1183,7 @@ 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)