kasan: sanitize objects when metadata doesn't fit

KASAN marks caches that are sanitized with the SLAB_KASAN cache flag.
Currently if the metadata that is appended after the object (stores e.g.
stack trace ids) doesn't fit into KMALLOC_MAX_SIZE (can only happen with
SLAB, see the comment in the patch), KASAN turns off sanitization
completely.

With this change sanitization of the object data is always enabled.
However the metadata is only stored when it fits.  Instead of checking for
SLAB_KASAN flag accross the code to find out whether the metadata is
there, use cache->kasan_info.alloc/free_meta_offset.  As 0 can be a valid
value for free_meta_offset, introduce KASAN_NO_FREE_META as an indicator
that the free metadata is missing.

Without this change all sanitized KASAN objects would be put into
quarantine with generic KASAN.  With this change, only the objects that
have metadata (i.e.  when it fits) are put into quarantine, the rest is
freed right away.

Along the way rework __kasan_cache_create() and add claryfying comments.

Link: https://lkml.kernel.org/r/aee34b87a5e4afe586c2ac6a0b32db8dc4dcc2dc.1606162397.git.andreyknvl@google.com
Link: https://linux-review.googlesource.com/id/Icd947e2bea054cb5cfbdc6cf6652227d97032dcb
Co-developed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Signed-off-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index ca43de9811de..cc4d9e1d49b1 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -155,20 +155,31 @@ struct kasan_alloc_meta {
 struct qlist_node {
 	struct qlist_node *next;
 };
+
+/*
+ * Generic mode either stores free meta in the object itself or in the redzone
+ * after the object. In the former case free meta offset is 0, in the latter
+ * case it has some sane value smaller than INT_MAX. Use INT_MAX as free meta
+ * offset when free meta isn't present.
+ */
+#define KASAN_NO_FREE_META INT_MAX
+
 struct kasan_free_meta {
+#ifdef CONFIG_KASAN_GENERIC
 	/* This field is used while the object is in the quarantine.
 	 * Otherwise it might be used for the allocator freelist.
 	 */
 	struct qlist_node quarantine_link;
-#ifdef CONFIG_KASAN_GENERIC
 	struct kasan_track free_track;
 #endif
 };
 
 struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
 						const void *object);
+#ifdef CONFIG_KASAN_GENERIC
 struct kasan_free_meta *kasan_get_free_meta(struct kmem_cache *cache,
 						const void *object);
+#endif
 
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 
@@ -233,11 +244,11 @@ struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
 
 #if defined(CONFIG_KASAN_GENERIC) && \
 	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
-void quarantine_put(struct kmem_cache *cache, void *object);
+bool quarantine_put(struct kmem_cache *cache, void *object);
 void quarantine_reduce(void);
 void quarantine_remove_cache(struct kmem_cache *cache);
 #else
-static inline void quarantine_put(struct kmem_cache *cache, void *object) { }
+static inline bool quarantine_put(struct kmem_cache *cache, void *object) { return false; }
 static inline void quarantine_reduce(void) { }
 static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
 #endif