diff mbox series

[v3,15/34] mm: slub: Unpoison the memchr_inv() return value

Message ID 20231213233605.661251-16-iii@linux.ibm.com
State New
Headers
Series kmsan: Enable on s390 |

Commit Message

Ilya Leoshkevich Dec. 13, 2023, 11:24 p.m. UTC 
  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>
---
 mm/slub.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Vlastimil Babka Jan. 2, 2024, 4:10 p.m. UTC | #1 
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 <vbabka@suse.cz>

> ---
>  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)
diff mbox series

Patch

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)