From: Kees Cook <keescook@xxxxxxxxxxxx> Subject: mm/slab: validate cache membership under freelist hardening Patch series "mm/slab: Improved sanity checking". This adds defenses against slab cache confusion (as seen in real-world exploits[1]) and gracefully handles type confusions when trying to look up slab caches from an arbitrary page. (Also is patch 3: new LKDTM tests for these defenses as well as for the existing double-free detection. This patch (of 3): When building under CONFIG_SLAB_FREELIST_HARDENING, it makes sense to perform sanity-checking on the assumed slab cache during kmem_cache_free() to make sure the kernel doesn't mix freelists across slab caches and corrupt memory (as seen in the exploitation of flaws like CVE-2018-9568[1]). Note that the prior code might WARN() but still corrupt memory (i.e. return the assumed cache instead of the owned cache). There is no noticeable performance impact (changes are within noise). Measuring parallel kernel builds, I saw the following with CONFIG_SLAB_FREELIST_HARDENED, before and after this patch: before: Run times: 288.85 286.53 287.09 287.07 287.21 Min: 286.53 Max: 288.85 Mean: 287.35 Std Dev: 0.79 after: Run times: 289.58 287.40 286.97 287.20 287.01 Min: 286.97 Max: 289.58 Mean: 287.63 Std Dev: 0.99 Delta: 0.1% which is well below the standard deviation [1] https://github.com/ThomasKing2014/slides/raw/master/Building%20universal%20Android%20rooting%20with%20a%20type%20confusion%20vulnerability.pdf Link: http://lkml.kernel.org/r/20190530045017.15252-2-keescook@xxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Alexander Popov <alex.popov@xxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/slab.h | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) --- a/mm/slab.h~mm-slab-validate-cache-membership-under-freelist-hardening +++ a/mm/slab.h @@ -310,7 +310,7 @@ static inline bool is_root_cache(struct static inline bool slab_equal_or_root(struct kmem_cache *s, struct kmem_cache *p) { - return true; + return s == p; } static inline const char *cache_name(struct kmem_cache *s) @@ -363,18 +363,16 @@ static inline struct kmem_cache *cache_f * will also be a constant. */ if (!memcg_kmem_enabled() && + !IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && !unlikely(s->flags & SLAB_CONSISTENCY_CHECKS)) return s; page = virt_to_head_page(x); cachep = page->slab_cache; - if (slab_equal_or_root(cachep, s)) - return cachep; - - pr_err("%s: Wrong slab cache. %s but object is from %s\n", - __func__, s->name, cachep->name); - WARN_ON_ONCE(1); - return s; + WARN_ONCE(!slab_equal_or_root(cachep, s), + "%s: Wrong slab cache. %s but object is from %s\n", + __func__, s->name, cachep->name); + return cachep; } static inline size_t slab_ksize(const struct kmem_cache *s) _
