Re: [PATCH v7 18/38] mm: slub: Disable KMSAN when checking the padding bytes
From: Vlastimil Babka <hidden>
Date: 2024-06-24 07:34:40
Also in:
linux-mm, linux-s390, lkml
On 6/21/24 1:35 PM, 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`. 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. Reviewed-by: Alexander Potapenko <glider@google.com> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Vlastimil Babka <redacted>
quoted hunk ↗ jump to hunk
--- mm/slub.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)diff --git a/mm/slub.c b/mm/slub.c index b050e528112c..fcd68fcea4ab 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;