The patch titled
Subject: mm, kcsan: instrument SLAB/SLUB free with "ASSERT_EXCLUSIVE_ACCESS"
has been added to the -mm tree. Its filename is
mm-kcsan-instrument-slab-slub-free-with-assert_exclusive_access.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-kcsan-instrument-slab-slub-free-with-assert_exclusive_access.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-kcsan-instrument-slab-slub-free-with-assert_exclusive_access.patch
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------------------------------------------------------
From: Marco Elver <elver@xxxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20200616125617.237428-1-elver@xxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab.c | 4 ++++
mm/slub.c | 4 ++++
2 files changed, 8 insertions(+)
--- a/mm/slab.c~mm-kcsan-instrument-slab-slub-free-with-assert_exclusive_access
+++ a/mm/slab.c
@@ -3426,6 +3426,10 @@ static __always_inline void __cache_free
if (kasan_slab_free(cachep, objp, _RET_IP_))
return;
+ /* Use KCSAN to help debug racy use-after-free. */
+ __kcsan_check_access(objp, cachep->object_size,
+ KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT);
+
___cache_free(cachep, objp, caller);
}
--- a/mm/slub.c~mm-kcsan-instrument-slab-slub-free-with-assert_exclusive_access
+++ a/mm/slub.c
@@ -1470,6 +1470,10 @@ static __always_inline bool slab_free_ho
if (!(s->flags & SLAB_DEBUG_OBJECTS))
debug_check_no_obj_freed(x, s->object_size);
+ /* Use KCSAN to help debug racy use-after-free. */
+ __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_);
}
_
Patches currently in -mm which might be from elver@xxxxxxxxxx are
mm-kcsan-instrument-slab-slub-free-with-assert_exclusive_access.patch
