mm: kasan: initial memory quarantine implementation

Quarantine isolates freed objects in a separate queue.  The objects are
returned to the allocator later, which helps to detect use-after-free
errors.

When the object is freed, its state changes from KASAN_STATE_ALLOC to
KASAN_STATE_QUARANTINE.  The object is poisoned and put into quarantine
instead of being returned to the allocator, therefore every subsequent
access to that object triggers a KASAN error, and the error handler is
able to say where the object has been allocated and deallocated.

When it's time for the object to leave quarantine, its state becomes
KASAN_STATE_FREE and it's returned to the allocator.  From now on the
allocator may reuse it for another allocation.  Before that happens,
it's still possible to detect a use-after free on that object (it
retains the allocation/deallocation stacks).

When the allocator reuses this object, the shadow is unpoisoned and old
allocation/deallocation stacks are wiped.  Therefore a use of this
object, even an incorrect one, won't trigger ASan warning.

Without the quarantine, it's not guaranteed that the objects aren't
reused immediately, that's why the probability of catching a
use-after-free is lower than with quarantine in place.

Quarantine isolates freed objects in a separate queue.  The objects are
returned to the allocator later, which helps to detect use-after-free
errors.

Freed objects are first added to per-cpu quarantine queues.  When a
cache is destroyed or memory shrinking is requested, the objects are
moved into the global quarantine queue.  Whenever a kmalloc call allows
memory reclaiming, the oldest objects are popped out of the global queue
until the total size of objects in quarantine is less than 3/4 of the
maximum quarantine size (which is a fraction of installed physical
memory).

As long as an object remains in the quarantine, KASAN is able to report
accesses to it, so the chance of reporting a use-after-free is
increased.  Once the object leaves quarantine, the allocator may reuse
it, in which case the object is unpoisoned and KASAN can't detect
incorrect accesses to it.

Right now quarantine support is only enabled in SLAB allocator.
Unification of KASAN features in SLAB and SLUB will be done later.

This patch is based on the "mm: kasan: quarantine" patch originally
prepared by Dmitry Chernenkov.  A number of improvements have been
suggested by Andrey Ryabinin.

[glider@google.com: v9]
  Link: http://lkml.kernel.org/r/1462987130-144092-1-git-send-email-glider@google.com
Signed-off-by: Alexander Potapenko <glider@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>
Cc: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kasan.h

@@ -50,6 +50,8 @@ void kasan_free_pages(struct page *page, unsigned int order);
 
 void kasan_cache_create(struct kmem_cache *cache, size_t *size,
 			unsigned long *flags);
+void kasan_cache_shrink(struct kmem_cache *cache);
+void kasan_cache_destroy(struct kmem_cache *cache);
 
 void kasan_poison_slab(struct page *page);
 void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
@@ -63,7 +65,8 @@ void kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
 void kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
 
 void kasan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags);
-void kasan_slab_free(struct kmem_cache *s, void *object);
+bool kasan_slab_free(struct kmem_cache *s, void *object);
+void kasan_poison_slab_free(struct kmem_cache *s, void *object);
 
 struct kasan_cache {
 	int alloc_meta_offset;
@@ -88,6 +91,8 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
 static inline void kasan_cache_create(struct kmem_cache *cache,
 				      size_t *size,
 				      unsigned long *flags) {}
+static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
+static inline void kasan_cache_destroy(struct kmem_cache *cache) {}
 
 static inline void kasan_poison_slab(struct page *page) {}
 static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
@@ -105,7 +110,11 @@ static inline void kasan_krealloc(const void *object, size_t new_size,
 
 static inline void kasan_slab_alloc(struct kmem_cache *s, void *object,
 				   gfp_t flags) {}
-static inline void kasan_slab_free(struct kmem_cache *s, void *object) {}
+static inline bool kasan_slab_free(struct kmem_cache *s, void *object)
+{
+	return false;
+}
+static inline void kasan_poison_slab_free(struct kmem_cache *s, void *object) {}
 
 static inline int kasan_module_alloc(void *addr, size_t size) { return 0; }
 static inline void kasan_free_shadow(const struct vm_struct *vm) {}

mm/kasan/Makefile

@@ -8,3 +8,4 @@ CFLAGS_REMOVE_kasan.o = -pg
 CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
 obj-y := kasan.o report.o kasan_init.o
+obj-$(CONFIG_SLAB) += quarantine.o

mm/kasan/kasan.c

@@ -388,6 +388,16 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size,
 }
 #endif
 
+void kasan_cache_shrink(struct kmem_cache *cache)
+{
+	quarantine_remove_cache(cache);
+}
+
+void kasan_cache_destroy(struct kmem_cache *cache)
+{
+	quarantine_remove_cache(cache);
+}
+
 void kasan_poison_slab(struct page *page)
 {
 	kasan_poison_shadow(page_address(page),
@@ -482,7 +492,7 @@ void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
 	kasan_kmalloc(cache, object, cache->object_size, flags);
 }
 
-void kasan_slab_free(struct kmem_cache *cache, void *object)
+void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
 {
 	unsigned long size = cache->object_size;
 	unsigned long rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
@@ -491,18 +501,43 @@ void kasan_slab_free(struct kmem_cache *cache, void *object)
 	if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
 		return;
 
+	kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
+}
+
+bool kasan_slab_free(struct kmem_cache *cache, void *object)
+{
 #ifdef CONFIG_SLAB
-	if (cache->flags & SLAB_KASAN) {
-		struct kasan_free_meta *free_info =
-			get_free_info(cache, object);
+	/* RCU slabs could be legally used after free within the RCU period */
+	if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
+		return false;
+
+	if (likely(cache->flags & SLAB_KASAN)) {
 		struct kasan_alloc_meta *alloc_info =
 			get_alloc_info(cache, object);
-		alloc_info->state = KASAN_STATE_FREE;
-		set_track(&free_info->track, GFP_NOWAIT);
+		struct kasan_free_meta *free_info =
+			get_free_info(cache, object);
+
+		switch (alloc_info->state) {
+		case KASAN_STATE_ALLOC:
+			alloc_info->state = KASAN_STATE_QUARANTINE;
+			quarantine_put(free_info, cache);
+			set_track(&free_info->track, GFP_NOWAIT);
+			kasan_poison_slab_free(cache, object);
+			return true;
+		case KASAN_STATE_QUARANTINE:
+		case KASAN_STATE_FREE:
+			pr_err("Double free");
+			dump_stack();
+			break;
+		default:
+			break;
+		}
 	}
+	return false;
+#else
+	kasan_poison_slab_free(cache, object);
+	return false;
 #endif
-
-	kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
 }
 
 void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
@@ -511,6 +546,9 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 	unsigned long redzone_start;
 	unsigned long redzone_end;
 
+	if (flags & __GFP_RECLAIM)
+		quarantine_reduce();
+
 	if (unlikely(object == NULL))
 		return;
 
@@ -541,6 +579,9 @@ void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
 	unsigned long redzone_start;
 	unsigned long redzone_end;
 
+	if (flags & __GFP_RECLAIM)
+		quarantine_reduce();
+
 	if (unlikely(ptr == NULL))
 		return;
 

mm/kasan/kasan.h

@@ -62,6 +62,7 @@ struct kasan_global {
 enum kasan_state {
 	KASAN_STATE_INIT,
 	KASAN_STATE_ALLOC,
+	KASAN_STATE_QUARANTINE,
 	KASAN_STATE_FREE
 };
 
@@ -79,9 +80,14 @@ struct kasan_alloc_meta {
 	u32 reserved;
 };
 
+struct qlist_node {
+	struct qlist_node *next;
+};
 struct kasan_free_meta {
-	/* Allocator freelist pointer, unused by KASAN. */
-	void **freelist;
+	/* 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;
 	struct kasan_track track;
 };
 
@@ -105,4 +111,15 @@ static inline bool kasan_report_enabled(void)
 void kasan_report(unsigned long addr, size_t size,
 		bool is_write, unsigned long ip);
 
+#ifdef CONFIG_SLAB
+void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
+void quarantine_reduce(void);
+void quarantine_remove_cache(struct kmem_cache *cache);
+#else
+static inline void quarantine_put(struct kasan_free_meta *info,
+				struct kmem_cache *cache) { }
+static inline void quarantine_reduce(void) { }
+static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
+#endif
+
 #endif