mm: slub: disable KMSAN when checking the padding bytes

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`.

One possibility to fix this, since the intention behind guarding
memchr_inv() behind metadata_access_enable() is to touch poisoned metadata
without triggering KMSAN, is to unpoison its return value.  However, this
approach is too fragile.  So simply disable the KMSAN checks in the
respective functions.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ilya Leoshkevich <[email protected]>
Reviewed-by: Alexander Potapenko <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Hyeonggon Yoo <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Masami Hiramatsu (Google) <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Steven Rostedt (Google) <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 12 insertions, 4 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 10e396e1d495..177ad7d3288b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1176,9 +1176,16 @@ static void restore_bytes(struct kmem_cache *s, char *message, u8 data,
 	memset(from, data, to - from);
 }
 
-static int check_bytes_and_report(struct kmem_cache *s, struct slab *slab,
-			u8 *object, char *what,
-			u8 *start, unsigned int value, unsigned int bytes)
+#ifdef CONFIG_KMSAN
+#define pad_check_attributes noinline __no_kmsan_checks
+#else
+#define pad_check_attributes
+#endif
+
+static pad_check_attributes int
+check_bytes_and_report(struct kmem_cache *s, struct slab *slab,
+		       u8 *object, char *what,
+		       u8 *start, unsigned int value, unsigned int bytes)
 {
 	u8 *fault;
 	u8 *end;
@@ -1270,7 +1277,8 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
 }
 
 /* Check the pad bytes at the end of a slab page */
-static void slab_pad_check(struct kmem_cache *s, struct slab *slab)
+static pad_check_attributes void
+slab_pad_check(struct kmem_cache *s, struct slab *slab)
 {
 	u8 *start;
 	u8 *fault;