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kmsan: support SLAB_POISON

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Avoid false KMSAN negatives with SLUB_DEBUG by allowing kmsan_slab_free()
to poison the freed memory, and by preventing init_object() from
unpoisoning new allocations by using __memset().

There are two alternatives to this approach.  First, init_object() can be
marked with __no_sanitize_memory.  This annotation should be used with
great care, because it drops all instrumentation from the function, and
any shadow writes will be lost.  Even though this is not a concern with
the current init_object() implementation, this may change in the future.

Second, kmsan_poison_memory() calls may be added after memset() calls. 
The downside is that init_object() is called from free_debug_processing(),
in which case poisoning will erase the distinction between simply
uninitialized memory and UAF.

Link: https://lkml.kernel.org/r/20240621113706.315500-14-iii@linux.ibm.com
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <kasan-dev@googlegroups.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ilya Leoshkevich 2024-06-21 13:34:57 +02:00 committed by Andrew Morton
parent 1fdb3c7006
commit f416817197
2 changed files with 12 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
mm/kmsan/hooks.c
View File

@ -74,7 +74,7 @@ void kmsan_slab_free(struct kmem_cache *s, void *object)
return;
/* RCU slabs could be legally used after free within the RCU period */
if (unlikely(s->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)))
if (unlikely(s->flags & SLAB_TYPESAFE_BY_RCU))
return;
/*
* If there's a constructor, freed memory must remain in the same state

15
mm/slub.c
View File

@ -1139,7 +1139,13 @@ static void init_object(struct kmem_cache *s, void *object, u8 val)
unsigned int poison_size = s->object_size;
if (s->flags & SLAB_RED_ZONE) {
memset(p - s->red_left_pad, val, s->red_left_pad);
/*
* Here and below, avoid overwriting the KMSAN shadow. Keeping
* the shadow makes it possible to distinguish uninit-value
* from use-after-free.
*/
memset_no_sanitize_memory(p - s->red_left_pad, val,
s->red_left_pad);
if (slub_debug_orig_size(s) && val == SLUB_RED_ACTIVE) {
/*
@ -1152,12 +1158,13 @@ static void init_object(struct kmem_cache *s, void *object, u8 val)
}
if (s->flags & __OBJECT_POISON) {
memset(p, POISON_FREE, poison_size - 1);
p[poison_size - 1] = POISON_END;
memset_no_sanitize_memory(p, POISON_FREE, poison_size - 1);
memset_no_sanitize_memory(p + poison_size - 1, POISON_END, 1);
}
if (s->flags & SLAB_RED_ZONE)
memset(p + poison_size, val, s->inuse - poison_size);
memset_no_sanitize_memory(p + poison_size, val,
s->inuse - poison_size);
}
static void restore_bytes(struct kmem_cache *s, char *message, u8 data,