[PATCH v2 2/3] kasan: record and print the free track

[Walter Wu]

In order not to enlarge slub meta-data size, so we move free track
from slub meta-data (struct kasan_alloc_meta) into freed object.

Modification of struct kasan_alloc_meta:
- add two call_rcu() stack into kasan_alloc_meta, size is 8 bytes.
- remove free track from kasan_alloc_meta, size is 8 bytes.

Because free track is stored in freed object, so that if it is an
allocation objects, then it will not have free track information in
KASAN report.

This feature is only suitable for generic KASAN, because we need to
know whether objects are allocation or free.
- if slub object is allocation state, it will not print free stack.
- if slub oeject is free state, it will print free stack.

[1]https://bugzilla.kernel.org/show_bug.cgi?id=198437

Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
---
 mm/kasan/common.c  | 22 ++--------------------
 mm/kasan/generic.c | 22 ++++++++++++++++++++++
 mm/kasan/kasan.h   |  4 ++++
 mm/kasan/report.c  | 28 +++++-----------------------
 mm/kasan/tags.c    | 37 +++++++++++++++++++++++++++++++++++++
 5 files changed, 70 insertions(+), 43 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 8bc618289bb1..47b53912f322 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -51,7 +51,7 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags)
 	return stack_depot_save(entries, nr_entries, flags);
 }
 
-static inline void set_track(struct kasan_track *track, gfp_t flags)
+void kasan_set_track(struct kasan_track *track, gfp_t flags)
 {
 	track->pid = current->pid;
 	track->stack = kasan_save_stack(flags);
@@ -299,24 +299,6 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
 	return (void *)object + cache->kasan_info.free_meta_offset;
 }
 
-
-static void kasan_set_free_info(struct kmem_cache *cache,
-		void *object, u8 tag)
-{
-	struct kasan_alloc_meta *alloc_meta;
-	u8 idx = 0;
-
-	alloc_meta = get_alloc_info(cache, object);
-
-#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
-	idx = alloc_meta->free_track_idx;
-	alloc_meta->free_pointer_tag[idx] = tag;
-	alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
-#endif
-
-	set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
-}
-
 void kasan_poison_slab(struct page *page)
 {
 	unsigned long i;
@@ -492,7 +474,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
 		KASAN_KMALLOC_REDZONE);
 
 	if (cache->flags & SLAB_KASAN)
-		set_track(&get_alloc_info(cache, object)->alloc_track, flags);
+		kasan_set_track(&get_alloc_info(cache, object)->alloc_track, flags);
 
 	return set_tag(object, tag);
 }
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index b86880c338e2..dacff05a8107 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -354,3 +354,25 @@ struct kasan_track *kasan_get_aux_stack(struct kasan_alloc_meta *alloc_info,
 	return container_of(&alloc_info->rcu_stack[idx],
 						struct kasan_track, stack);
 }
+
+void kasan_set_free_info(struct kmem_cache *cache,
+						void *object, u8 tag)
+{
+	/* store free track into freed object */
+	kasan_set_track((struct kasan_track *)(object + SIZEOF_PTR), GFP_NOWAIT);
+}
+
+struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
+						void *object, u8 tag, const void *addr)
+{
+	u8 *shadow_addr = (u8 *)kasan_mem_to_shadow(addr);
+
+	/*
+	 * Only the freed object can get free track,
+	 * because free track information is stored to freed object.
+	 */
+	if (*shadow_addr == KASAN_KMALLOC_FREE)
+		return (struct kasan_track *)(object + SIZEOF_PTR);
+	else
+		return NULL;
+}
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 1cc1fb7b0de3..f88d13f86ed3 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -173,6 +173,10 @@ void kasan_report_invalid_free(void *object, unsigned long ip);
 struct page *kasan_addr_to_page(const void *addr);
 
 depot_stack_handle_t kasan_save_stack(gfp_t flags);
+void kasan_set_track(struct kasan_track *track, gfp_t flags);
+void kasan_set_free_info(struct kmem_cache *cache, void *object, u8 tag);
+struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
+				void *object, u8 tag, const void *addr);
 
 #if defined(CONFIG_KASAN_GENERIC) && \
 	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index f16a1a210815..51813f02992c 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -163,26 +163,6 @@ static void describe_object_addr(struct kmem_cache *cache, void *object,
 		(void *)(object_addr + cache->object_size));
 }
 
-static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
-		void *object, u8 tag)
-{
-	struct kasan_alloc_meta *alloc_meta;
-	int i = 0;
-
-	alloc_meta = get_alloc_info(cache, object);
-
-#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
-	for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
-		if (alloc_meta->free_pointer_tag[i] == tag)
-			break;
-	}
-	if (i == KASAN_NR_FREE_STACKS)
-		i = alloc_meta->free_track_idx;
-#endif
-
-	return &alloc_meta->free_track[i];
-}
-
 static void describe_object(struct kmem_cache *cache, void *object,
 				const void *addr, u8 tag)
 {
@@ -193,9 +173,11 @@ static void describe_object(struct kmem_cache *cache, void *object,
 
 		print_track(&alloc_info->alloc_track, "Allocated", false);
 		pr_err("\n");
-		free_track = kasan_get_free_track(cache, object, tag);
-		print_track(free_track, "Freed", false);
-		pr_err("\n");
+		free_track = kasan_get_free_track(cache, object, tag, addr);
+		if (free_track) {
+			print_track(free_track, "Freed", false);
+			pr_err("\n");
+		}
 
 		if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
 			free_track = kasan_get_aux_stack(alloc_info, 0);
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 25b7734e7013..30a27f8c1e6e 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -162,3 +162,40 @@ void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
 	kasan_poison_shadow((void *)addr, size, tag);
 }
 EXPORT_SYMBOL(__hwasan_tag_memory);
+
+void kasan_set_free_info(struct kmem_cache *cache,
+		void *object, u8 tag)
+{
+	struct kasan_alloc_meta *alloc_meta;
+	u8 idx = 0;
+
+	alloc_meta = get_alloc_info(cache, object);
+
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+	idx = alloc_meta->free_track_idx;
+	alloc_meta->free_pointer_tag[idx] = tag;
+	alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
+#endif
+
+	kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
+}
+
+struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
+		void *object, u8 tag, const void *addr)
+{
+	struct kasan_alloc_meta *alloc_meta;
+	int i = 0;
+
+	alloc_meta = get_alloc_info(cache, object);
+
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+	for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
+		if (alloc_meta->free_pointer_tag[i] == tag)
+			break;
+	}
+	if (i == KASAN_NR_FREE_STACKS)
+		i = alloc_meta->free_track_idx;
+#endif
+
+	return &alloc_meta->free_track[i];
+}
-- 
2.18.0