mm, kcsan: instrument SLAB/SLUB free with "ASSERT_EXCLUSIVE_ACCESS"

Provide the necessary KCSAN checks to assist with debugging racy
use-after-frees.  While KASAN is more reliable at generally catching such
use-after-frees (due to its use of a quarantine), it can be difficult to
debug racy use-after-frees.  If a reliable reproducer exists, KCSAN can
assist in debugging such issues.

Note: ASSERT_EXCLUSIVE_ACCESS is a convenience wrapper if the size is
simply sizeof(var).  Instead, here we just use __kcsan_check_access()
explicitly to pass the correct size.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200623072653.114563-1-elver@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab.c b/mm/slab.c
index 390e249..fa31cbb 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3432,6 +3432,11 @@ static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp,
        if (kasan_slab_free(cachep, objp, _RET_IP_))
                return;
 
+       /* Use KCSAN to help debug racy use-after-free. */
+       if (!(cachep->flags & SLAB_TYPESAFE_BY_RCU))
+               __kcsan_check_access(objp, cachep->object_size,
+                                    KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT);
+
        ___cache_free(cachep, objp, caller);
 }
 

diff --git a/mm/slub.c b/mm/slub.c
index e5fc31c..ae39eb3 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1549,6 +1549,11 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s, void *x)
        if (!(s->flags & SLAB_DEBUG_OBJECTS))
                debug_check_no_obj_freed(x, s->object_size);
 
+       /* Use KCSAN to help debug racy use-after-free. */
+       if (!(s->flags & SLAB_TYPESAFE_BY_RCU))
+               __kcsan_check_access(x, s->object_size,
+                                    KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT);
+
        /* KASAN might put x into memory quarantine, delaying its reuse */
        return kasan_slab_free(s, x, _RET_IP_);
 }