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@xxxxxxxxxx> --- mm/slab.c | 4 ++++ mm/slub.c | 4 ++++ 2 files changed, 8 insertions(+) diff --git a/mm/slab.c b/mm/slab.c index 9350062ffc1a..4c7013eeacd9 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3426,6 +3426,10 @@ 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. */ + __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 b8f798b50d44..57db6ca2e0dc 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1470,6 +1470,10 @@ 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. */ + __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_); } -- 2.27.0.290.gba653c62da-goog
