mm/kasan: get rid of ->state in struct kasan_alloc_meta

The state of object currently tracked in two places - shadow memory, and
the ->state field in struct kasan_alloc_meta.  We can get rid of the
latter.  The will save us a little bit of memory.  Also, this allow us
to move free stack into struct kasan_alloc_meta, without increasing
memory consumption.  So now we should always know when the last time the
object was freed.  This may be useful for long delayed use-after-free
bugs.

As a side effect this fixes following UBSAN warning:
	UBSAN: Undefined behaviour in mm/kasan/quarantine.c:102:13
	member access within misaligned address ffff88000d1efebc for type 'struct qlist_node'
	which requires 8 byte alignment

Link: http://lkml.kernel.org/r/1470062715-14077-5-git-send-email-aryabinin@virtuozzo.com
Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

7 files changed, 42 insertions, 64 deletions

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index c9cf374445d8..d600303306eb 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -56,6 +56,7 @@ 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);
 void kasan_poison_object_data(struct kmem_cache *cache, void *object);
+void kasan_init_slab_obj(struct kmem_cache *cache, const void *object);
 
 void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
 void kasan_kfree_large(const void *ptr);
@@ -102,6 +103,8 @@ static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
                                         void *object) {}
 static inline void kasan_poison_object_data(struct kmem_cache *cache,
                                         void *object) {}
+static inline void kasan_init_slab_obj(struct kmem_cache *cache,
+                                const void *object) {}
 
 static inline void kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags) {}
 static inline void kasan_kfree_large(const void *ptr) {}
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 388e812ccaca..92750e3b0083 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -442,11 +442,6 @@ void kasan_poison_object_data(struct kmem_cache *cache, void *object)
         kasan_poison_shadow(object,
                         round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
                         KASAN_KMALLOC_REDZONE);
-        if (cache->flags & SLAB_KASAN) {
-                struct kasan_alloc_meta *alloc_info =
-                        get_alloc_info(cache, object);
-                alloc_info->state = KASAN_STATE_INIT;
-        }
 }
 
 static inline int in_irqentry_text(unsigned long ptr)
@@ -510,6 +505,17 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
         return (void *)object + cache->kasan_info.free_meta_offset;
 }
 
+void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)
+{
+        struct kasan_alloc_meta *alloc_info;
+
+        if (!(cache->flags & SLAB_KASAN))
+                return;
+
+        alloc_info = get_alloc_info(cache, object);
+        __memset(alloc_info, 0, sizeof(*alloc_info));
+}
+
 void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
 {
         kasan_kmalloc(cache, object, cache->object_size, flags);
@@ -529,34 +535,27 @@ static void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
 
 bool kasan_slab_free(struct kmem_cache *cache, void *object)
 {
+        s8 shadow_byte;
+
         /* 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;
-                struct kasan_free_meta *free_info;
+        shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
+        if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
+                pr_err("Double free");
+                dump_stack();
+                return true;
+        }
 
-                alloc_info = get_alloc_info(cache, object);
-                free_info = get_free_info(cache, object);
+        kasan_poison_slab_free(cache, object);
 
-                switch (alloc_info->state) {
-                case KASAN_STATE_ALLOC:
-                        alloc_info->state = KASAN_STATE_QUARANTINE;
-                        set_track(&free_info->track, GFP_NOWAIT);
-                        kasan_poison_slab_free(cache, object);
-                        quarantine_put(free_info, cache);
-                        return true;
-                case KASAN_STATE_QUARANTINE:
-                case KASAN_STATE_FREE:
-                        pr_err("Double free");
-                        dump_stack();
-                        break;
-                default:
-                        break;
-                }
-        }
-        return false;
+        if (unlikely(!(cache->flags & SLAB_KASAN)))
+                return false;
+
+        set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
+        quarantine_put(get_free_info(cache, object), cache);
+        return true;
 }
 
 void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
@@ -579,13 +578,9 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
         kasan_unpoison_shadow(object, size);
         kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
                 KASAN_KMALLOC_REDZONE);
-        if (cache->flags & SLAB_KASAN) {
-                struct kasan_alloc_meta *alloc_info =
-                        get_alloc_info(cache, object);
 
-                alloc_info->state = KASAN_STATE_ALLOC;
-                set_track(&alloc_info->track, flags);
-        }
+        if (cache->flags & SLAB_KASAN)
+                set_track(&get_alloc_info(cache, object)->alloc_track, flags);
 }
 EXPORT_SYMBOL(kasan_kmalloc);
 
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index aa175460c8f9..9b7b31e25fd2 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -59,13 +59,6 @@ struct kasan_global {
  * Structures to keep alloc and free tracks *
  */
 
-enum kasan_state {
-        KASAN_STATE_INIT,
-        KASAN_STATE_ALLOC,
-        KASAN_STATE_QUARANTINE,
-        KASAN_STATE_FREE
-};
-
 #define KASAN_STACK_DEPTH 64
 
 struct kasan_track {
@@ -74,8 +67,8 @@ struct kasan_track {
 };
 
 struct kasan_alloc_meta {
-        struct kasan_track track;
-        u32 state;
+        struct kasan_track alloc_track;
+        struct kasan_track free_track;
 };
 
 struct qlist_node {
@@ -86,7 +79,6 @@ struct kasan_free_meta {
          * Otherwise it might be used for the allocator freelist.
          */
         struct qlist_node quarantine_link;
-        struct kasan_track track;
 };
 
 struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 4852625ff851..7fd121d13b88 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -144,13 +144,11 @@ static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
 {
         void *object = qlink_to_object(qlink, cache);
-        struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
         unsigned long flags;
 
         if (IS_ENABLED(CONFIG_SLAB))
                 local_irq_save(flags);
 
-        alloc_info->state = KASAN_STATE_FREE;
         ___cache_free(cache, object, _THIS_IP_);
 
         if (IS_ENABLED(CONFIG_SLAB))
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index d67a7e020905..f437398b685a 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -133,7 +133,6 @@ static void kasan_object_err(struct kmem_cache *cache, struct page *page,
                                 void *object, char *unused_reason)
 {
         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
-        struct kasan_free_meta *free_info;
 
         dump_stack();
         pr_err("Object at %p, in cache %s size: %d\n", object, cache->name,
@@ -141,23 +140,11 @@ static void kasan_object_err(struct kmem_cache *cache, struct page *page,
 
         if (!(cache->flags & SLAB_KASAN))
                 return;
-        switch (alloc_info->state) {
-        case KASAN_STATE_INIT:
-                pr_err("Object not allocated yet\n");
-                break;
-        case KASAN_STATE_ALLOC:
-                pr_err("Allocation:\n");
-                print_track(&alloc_info->track);
-                break;
-        case KASAN_STATE_FREE:
-        case KASAN_STATE_QUARANTINE:
-                free_info = get_free_info(cache, object);
-                pr_err("Allocation:\n");
-                print_track(&alloc_info->track);
-                pr_err("Deallocation:\n");
-                print_track(&free_info->track);
-                break;
-        }
+
+        pr_err("Allocated:\n");
+        print_track(&alloc_info->alloc_track);
+        pr_err("Freed:\n");
+        print_track(&alloc_info->free_track);
 }
 
 static void print_address_description(struct kasan_access_info *info)
diff --git a/mm/slab.c b/mm/slab.c
index 09771ed3e693..ca135bd47c35 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2604,9 +2604,11 @@ static void cache_init_objs(struct kmem_cache *cachep,
         }
 
         for (i = 0; i < cachep->num; i++) {
+                objp = index_to_obj(cachep, page, i);
+                kasan_init_slab_obj(cachep, objp);
+
                 /* constructor could break poison info */
                 if (DEBUG == 0 && cachep->ctor) {
-                        objp = index_to_obj(cachep, page, i);
                         kasan_unpoison_object_data(cachep, objp);
                         cachep->ctor(objp);
                         kasan_poison_object_data(cachep, objp);
diff --git a/mm/slub.c b/mm/slub.c
index 74e7c8c30db8..26eb6a99540e 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1384,6 +1384,7 @@ static void setup_object(struct kmem_cache *s, struct page *page,
                                 void *object)
 {
         setup_object_debug(s, page, object);
+        kasan_init_slab_obj(s, object);
         if (unlikely(s->ctor)) {
                 kasan_unpoison_object_data(s, object);
                 s->ctor(object);