Commit cfbe1636 authored Aug 06, 2020 by Marco Elver Committed by Linus Torvalds Aug 07, 2020

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>

parent b3cb9fc3

mm/slab.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}

mm/slub.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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_);
		}

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