[v6,2/4] kasan: record and print the free track
diff mbox series

Message ID 20200522020127.23335-1-walter-zh.wu@mediatek.com
State New, archived
Headers show
Series
  • kasan: memorize and print call_rcu stack
Related show

Commit Message

Walter Wu May 22, 2020, 2:01 a.m. UTC
Move free track from kasan_alloc_meta to kasan_free_meta in order
to make struct kasan_alloc_meta and kasan_free_meta size are both
16 bytes. It is a good size because it is the minimal redzone size
and a good number of alignment.

For free track, we make some modifications as shown below:
1) Remove the free_track from struct kasan_alloc_meta.
2) Add the free_track into struct kasan_free_meta.
3) Add a macro KASAN_KMALLOC_FREETRACK in order to check whether
   it can print free stack in KASAN report.

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

Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Co-developed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
---
 mm/kasan/common.c         | 22 ++--------------------
 mm/kasan/generic.c        | 22 ++++++++++++++++++++++
 mm/kasan/generic_report.c |  1 +
 mm/kasan/kasan.h          | 13 +++++++++++--
 mm/kasan/quarantine.c     |  1 +
 mm/kasan/report.c         | 26 ++++----------------------
 mm/kasan/tags.c           | 37 +++++++++++++++++++++++++++++++++++++
 7 files changed, 78 insertions(+), 44 deletions(-)

Comments

Dmitry Vyukov May 25, 2020, 9:56 a.m. UTC | #1
On Fri, May 22, 2020 at 4:01 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> Move free track from kasan_alloc_meta to kasan_free_meta in order
> to make struct kasan_alloc_meta and kasan_free_meta size are both
> 16 bytes. It is a good size because it is the minimal redzone size
> and a good number of alignment.
>
> For free track, we make some modifications as shown below:
> 1) Remove the free_track from struct kasan_alloc_meta.
> 2) Add the free_track into struct kasan_free_meta.
> 3) Add a macro KASAN_KMALLOC_FREETRACK in order to check whether
>    it can print free stack in KASAN report.
>
> [1]https://bugzilla.kernel.org/show_bug.cgi?id=198437

Reviewed-and-tested-by: Dmitry Vyukov <dvyukov@google.com>

> Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> Co-developed-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Alexander Potapenko <glider@google.com>
> ---
>  mm/kasan/common.c         | 22 ++--------------------
>  mm/kasan/generic.c        | 22 ++++++++++++++++++++++
>  mm/kasan/generic_report.c |  1 +
>  mm/kasan/kasan.h          | 13 +++++++++++--
>  mm/kasan/quarantine.c     |  1 +
>  mm/kasan/report.c         | 26 ++++----------------------
>  mm/kasan/tags.c           | 37 +++++++++++++++++++++++++++++++++++++
>  7 files changed, 78 insertions(+), 44 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 8acf48882ba2..4b3cbad7431b 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -346,3 +346,25 @@ void kasan_record_aux_stack(void *addr)
>         alloc_info->aux_stack[1] = alloc_info->aux_stack[0];
>         alloc_info->aux_stack[0] = kasan_save_stack(GFP_NOWAIT);
>  }
> +
> +void kasan_set_free_info(struct kmem_cache *cache,
> +                               void *object, u8 tag)
> +{
> +       struct kasan_free_meta *free_meta;
> +
> +       free_meta = get_free_info(cache, object);
> +       kasan_set_track(&free_meta->free_track, GFP_NOWAIT);
> +
> +       /*
> +        *  the object was freed and has free track set
> +        */
> +       *(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_FREETRACK;
> +}
> +
> +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> +                               void *object, u8 tag)
> +{
> +       if (*(u8 *)kasan_mem_to_shadow(object) != KASAN_KMALLOC_FREETRACK)
> +               return NULL;
> +       return &get_free_info(cache, object)->free_track;
> +}
> diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
> index e200acb2d292..a38c7a9e192a 100644
> --- a/mm/kasan/generic_report.c
> +++ b/mm/kasan/generic_report.c
> @@ -80,6 +80,7 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
>                 break;
>         case KASAN_FREE_PAGE:
>         case KASAN_KMALLOC_FREE:
> +       case KASAN_KMALLOC_FREETRACK:
>                 bug_type = "use-after-free";
>                 break;
>         case KASAN_ALLOCA_LEFT:
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index a7391bc83070..ef655a1c6e15 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -17,15 +17,17 @@
>  #define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */
>  #define KASAN_KMALLOC_REDZONE   0xFC  /* redzone inside slub object */
>  #define KASAN_KMALLOC_FREE      0xFB  /* object was freed (kmem_cache_free/kfree) */
> +#define KASAN_KMALLOC_FREETRACK 0xFA  /* object was freed and has free track set */
>  #else
>  #define KASAN_FREE_PAGE         KASAN_TAG_INVALID
>  #define KASAN_PAGE_REDZONE      KASAN_TAG_INVALID
>  #define KASAN_KMALLOC_REDZONE   KASAN_TAG_INVALID
>  #define KASAN_KMALLOC_FREE      KASAN_TAG_INVALID
> +#define KASAN_KMALLOC_FREETRACK KASAN_TAG_INVALID
>  #endif
>
> -#define KASAN_GLOBAL_REDZONE    0xFA  /* redzone for global variable */
> -#define KASAN_VMALLOC_INVALID   0xF9  /* unallocated space in vmapped page */
> +#define KASAN_GLOBAL_REDZONE    0xF9  /* redzone for global variable */
> +#define KASAN_VMALLOC_INVALID   0xF8  /* unallocated space in vmapped page */
>
>  /*
>   * Stack redzone shadow values
> @@ -127,6 +129,9 @@ struct kasan_free_meta {
>          * 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 *get_alloc_info(struct kmem_cache *cache,
> @@ -168,6 +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);
>
>  #if defined(CONFIG_KASAN_GENERIC) && \
>         (defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> index 978bc4a3eb51..4c5375810449 100644
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -145,6 +145,7 @@ static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
>         if (IS_ENABLED(CONFIG_SLAB))
>                 local_irq_save(flags);
>
> +       *(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_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 2421a4bd9227..fed3c8fdfd25 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -164,26 +164,6 @@ 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)
>  {
> @@ -195,8 +175,10 @@ static void describe_object(struct kmem_cache *cache, void *object,
>                 print_track(&alloc_info->alloc_track, "Allocated");
>                 pr_err("\n");
>                 free_track = kasan_get_free_track(cache, object, tag);
> -               print_track(free_track, "Freed");
> -               pr_err("\n");
> +               if (free_track) {
> +                       print_track(free_track, "Freed");
> +                       pr_err("\n");
> +               }
>
>  #ifdef CONFIG_KASAN_GENERIC
>                 if (alloc_info->aux_stack[0]) {
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index 25b7734e7013..201dee5d6ae0 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)
> +{
> +       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
>
> --
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Patch
diff mbox series

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 8acf48882ba2..4b3cbad7431b 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -346,3 +346,25 @@  void kasan_record_aux_stack(void *addr)
 	alloc_info->aux_stack[1] = alloc_info->aux_stack[0];
 	alloc_info->aux_stack[0] = kasan_save_stack(GFP_NOWAIT);
 }
+
+void kasan_set_free_info(struct kmem_cache *cache,
+				void *object, u8 tag)
+{
+	struct kasan_free_meta *free_meta;
+
+	free_meta = get_free_info(cache, object);
+	kasan_set_track(&free_meta->free_track, GFP_NOWAIT);
+
+	/*
+	 *  the object was freed and has free track set
+	 */
+	*(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_FREETRACK;
+}
+
+struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
+				void *object, u8 tag)
+{
+	if (*(u8 *)kasan_mem_to_shadow(object) != KASAN_KMALLOC_FREETRACK)
+		return NULL;
+	return &get_free_info(cache, object)->free_track;
+}
diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
index e200acb2d292..a38c7a9e192a 100644
--- a/mm/kasan/generic_report.c
+++ b/mm/kasan/generic_report.c
@@ -80,6 +80,7 @@  static const char *get_shadow_bug_type(struct kasan_access_info *info)
 		break;
 	case KASAN_FREE_PAGE:
 	case KASAN_KMALLOC_FREE:
+	case KASAN_KMALLOC_FREETRACK:
 		bug_type = "use-after-free";
 		break;
 	case KASAN_ALLOCA_LEFT:
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index a7391bc83070..ef655a1c6e15 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -17,15 +17,17 @@ 
 #define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */
 #define KASAN_KMALLOC_REDZONE   0xFC  /* redzone inside slub object */
 #define KASAN_KMALLOC_FREE      0xFB  /* object was freed (kmem_cache_free/kfree) */
+#define KASAN_KMALLOC_FREETRACK 0xFA  /* object was freed and has free track set */
 #else
 #define KASAN_FREE_PAGE         KASAN_TAG_INVALID
 #define KASAN_PAGE_REDZONE      KASAN_TAG_INVALID
 #define KASAN_KMALLOC_REDZONE   KASAN_TAG_INVALID
 #define KASAN_KMALLOC_FREE      KASAN_TAG_INVALID
+#define KASAN_KMALLOC_FREETRACK KASAN_TAG_INVALID
 #endif
 
-#define KASAN_GLOBAL_REDZONE    0xFA  /* redzone for global variable */
-#define KASAN_VMALLOC_INVALID   0xF9  /* unallocated space in vmapped page */
+#define KASAN_GLOBAL_REDZONE    0xF9  /* redzone for global variable */
+#define KASAN_VMALLOC_INVALID   0xF8  /* unallocated space in vmapped page */
 
 /*
  * Stack redzone shadow values
@@ -127,6 +129,9 @@  struct kasan_free_meta {
 	 * 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 *get_alloc_info(struct kmem_cache *cache,
@@ -168,6 +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);
 
 #if defined(CONFIG_KASAN_GENERIC) && \
 	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 978bc4a3eb51..4c5375810449 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -145,6 +145,7 @@  static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
 	if (IS_ENABLED(CONFIG_SLAB))
 		local_irq_save(flags);
 
+	*(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_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 2421a4bd9227..fed3c8fdfd25 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -164,26 +164,6 @@  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)
 {
@@ -195,8 +175,10 @@  static void describe_object(struct kmem_cache *cache, void *object,
 		print_track(&alloc_info->alloc_track, "Allocated");
 		pr_err("\n");
 		free_track = kasan_get_free_track(cache, object, tag);
-		print_track(free_track, "Freed");
-		pr_err("\n");
+		if (free_track) {
+			print_track(free_track, "Freed");
+			pr_err("\n");
+		}
 
 #ifdef CONFIG_KASAN_GENERIC
 		if (alloc_info->aux_stack[0]) {
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 25b7734e7013..201dee5d6ae0 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)
+{
+	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];
+}