[PATCH v4] kasan: add memory corruption identification for software tag-based mode

Walter Wu walter-zh.wu at mediatek.com
Mon Aug 5 22:43:40 PDT 2019


This patch adds memory corruption identification at bug report for
software tag-based mode, the report show whether it is "use-after-free"
or "out-of-bound" error instead of "invalid-access" error. This will make
it easier for programmers to see the memory corruption problem.

We extend the slab to store five old free pointer tag and free backtrace,
we can check if the tagged address is in the slab record and make a
good guess if the object is more like "use-after-free" or "out-of-bound".
therefore every slab memory corruption can be identified whether it's
"use-after-free" or "out-of-bound".

====== Changes
Change since v1:
- add feature option CONFIG_KASAN_SW_TAGS_IDENTIFY.
- change QUARANTINE_FRACTION to reduce quarantine size.
- change the qlist order in order to find the newest object in quarantine
- reduce the number of calling kmalloc() from 2 to 1 time.
- remove global variable to use argument to pass it.
- correct the amount of qobject cache->size into the byes of qlist_head.
- only use kasan_cache_shrink() to shink memory.

Change since v2:
- remove the shinking memory function kasan_cache_shrink()
- modify the description of the CONFIG_KASAN_SW_TAGS_IDENTIFY
- optimize the quarantine_find_object() and qobject_free()
- fix the duplicating function name 3 times in the header.
- modify the function name set_track() to kasan_set_track()

Change since v3:
- change tag-based quarantine to extend slab to identify memory corruption

Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov at google.com>
Signed-off-by: Walter Wu <walter-zh.wu at mediatek.com>
---
 lib/Kconfig.kasan      |  8 ++++
 mm/kasan/common.c      | 14 +++++--
 mm/kasan/kasan.h       | 37 ++++++++++++++++++
 mm/kasan/report.c      | 53 +++++++++++++++-----------
 mm/kasan/tags.c        | 86 ++++++++++++++++++++++++++++++++++++++++++
 mm/kasan/tags_report.c |  5 ++-
 6 files changed, 177 insertions(+), 26 deletions(-)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 4fafba1a923b..70b55e1c4834 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -135,6 +135,14 @@ config KASAN_S390_4_LEVEL_PAGING
 	  to 3TB of RAM with KASan enabled). This options allows to force
 	  4-level paging instead.
 
+config KASAN_SW_TAGS_IDENTIFY
+	bool "Enable memory corruption identification"
+	depends on KASAN_SW_TAGS
+	help
+	  This option enables best-effort identification of bug type
+	  (use-after-free or out-of-bounds) at the cost of increased
+	  memory consumption for slab extending.
+
 config TEST_KASAN
 	tristate "Module for testing KASAN for bug detection"
 	depends on m && KASAN
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 2277b82902d8..6bbb044708e6 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -71,7 +71,7 @@ static inline depot_stack_handle_t 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 = save_stack(flags);
@@ -304,7 +304,8 @@ size_t kasan_metadata_size(struct kmem_cache *cache)
 struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
 					const void *object)
 {
-	BUILD_BUG_ON(sizeof(struct kasan_alloc_meta) > 32);
+	if (!IS_ENABLED(CONFIG_KASAN_SW_TAGS_IDENTIFY))
+		BUILD_BUG_ON(sizeof(struct kasan_alloc_meta) > 32);
 	return (void *)object + cache->kasan_info.alloc_meta_offset;
 }
 
@@ -446,7 +447,11 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
 			unlikely(!(cache->flags & SLAB_KASAN)))
 		return false;
 
-	set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
+	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS_IDENTIFY))
+		kasan_set_free_info(cache, object, tag);
+	else
+		kasan_set_track(&get_alloc_info(cache, object)->free_track,
+						GFP_NOWAIT);
 	quarantine_put(get_free_info(cache, object), cache);
 
 	return IS_ENABLED(CONFIG_KASAN_GENERIC);
@@ -484,7 +489,8 @@ 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/kasan.h b/mm/kasan/kasan.h
index 014f19e76247..531a5823e8c6 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -95,9 +95,23 @@ struct kasan_track {
 	depot_stack_handle_t stack;
 };
 
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+#define KASAN_EXTRA_FREE_INFO_COUNT 4
+#define KASAN_TOTAL_FREE_INFO_COUNT  (KASAN_EXTRA_FREE_INFO_COUNT + 1)
+struct extra_free_info {
+	/* Round-robin FIFO array. */
+	struct kasan_track free_track[KASAN_EXTRA_FREE_INFO_COUNT];
+	u8 free_pointer_tag[KASAN_TOTAL_FREE_INFO_COUNT];
+	u8 free_track_tail;
+};
+#endif
+
 struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
 	struct kasan_track free_track;
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+	struct extra_free_info free_info;
+#endif
 };
 
 struct qlist_node {
@@ -146,6 +160,29 @@ void kasan_report(unsigned long addr, size_t size,
 		bool is_write, unsigned long ip);
 void kasan_report_invalid_free(void *object, unsigned long ip);
 
+struct page *addr_to_page(const void *addr);
+
+void kasan_set_track(struct kasan_track *track, gfp_t flags);
+
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+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);
+char *kasan_get_corruption_type(void *addr);
+#else
+static inline void kasan_set_free_info(struct kmem_cache *cache,
+		void *object, u8 tag) { }
+static inline struct kasan_track *kasan_get_free_track(
+		struct kmem_cache *cache, void *object, u8 tag)
+{
+	return NULL;
+}
+static inline char *kasan_get_corruption_type(void *addr)
+{
+	return NULL;
+}
+#endif
+
 #if defined(CONFIG_KASAN_GENERIC) && \
 	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 0e5f965f1882..9ea7a4265b42 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -111,14 +111,6 @@ static void print_track(struct kasan_track *track, const char *prefix)
 	}
 }
 
-static struct page *addr_to_page(const void *addr)
-{
-	if ((addr >= (void *)PAGE_OFFSET) &&
-			(addr < high_memory))
-		return virt_to_head_page(addr);
-	return NULL;
-}
-
 static void describe_object_addr(struct kmem_cache *cache, void *object,
 				const void *addr)
 {
@@ -152,18 +144,27 @@ static void describe_object_addr(struct kmem_cache *cache, void *object,
 }
 
 static void describe_object(struct kmem_cache *cache, void *object,
-				const void *addr)
+				const void *tagged_addr)
 {
+	void *untagged_addr = reset_tag(tagged_addr);
 	struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 
 	if (cache->flags & SLAB_KASAN) {
 		print_track(&alloc_info->alloc_track, "Allocated");
 		pr_err("\n");
-		print_track(&alloc_info->free_track, "Freed");
-		pr_err("\n");
+		if (IS_ENABLED(CONFIG_KASAN_SW_TAGS_IDENTIFY)) {
+			struct kasan_track *free_track;
+			u8 tag = get_tag(tagged_addr);
+
+			free_track = kasan_get_free_track(cache, object, tag);
+			print_track(free_track, "Freed");
+		} else {
+			print_track(&alloc_info->free_track, "Freed");
+			pr_err("\n");
+		}
 	}
 
-	describe_object_addr(cache, object, addr);
+	describe_object_addr(cache, object, untagged_addr);
 }
 
 static inline bool kernel_or_module_addr(const void *addr)
@@ -344,23 +345,25 @@ static void print_address_stack_frame(const void *addr)
 	print_decoded_frame_descr(frame_descr);
 }
 
-static void print_address_description(void *addr)
+static void print_address_description(void *tagged_addr)
 {
-	struct page *page = addr_to_page(addr);
+	void *untagged_addr = reset_tag(tagged_addr);
+	struct page *page = addr_to_page(untagged_addr);
 
 	dump_stack();
 	pr_err("\n");
 
 	if (page && PageSlab(page)) {
 		struct kmem_cache *cache = page->slab_cache;
-		void *object = nearest_obj(cache, page,	addr);
+		void *object = nearest_obj(cache, page,	untagged_addr);
 
-		describe_object(cache, object, addr);
+		describe_object(cache, object, tagged_addr);
 	}
 
-	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
+	if (kernel_or_module_addr(untagged_addr) &&
+			!init_task_stack_addr(untagged_addr)) {
 		pr_err("The buggy address belongs to the variable:\n");
-		pr_err(" %pS\n", addr);
+		pr_err(" %pS\n", tagged_addr);
 	}
 
 	if (page) {
@@ -368,7 +371,7 @@ static void print_address_description(void *addr)
 		dump_page(page, "kasan: bad access detected");
 	}
 
-	print_address_stack_frame(addr);
+	print_address_stack_frame(untagged_addr);
 }
 
 static bool row_is_guilty(const void *row, const void *guilty)
@@ -432,6 +435,14 @@ static bool report_enabled(void)
 	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 }
 
+struct page *addr_to_page(const void *addr)
+{
+	if ((addr >= (void *)PAGE_OFFSET) &&
+			(addr < high_memory))
+		return virt_to_head_page(addr);
+	return NULL;
+}
+
 void kasan_report_invalid_free(void *object, unsigned long ip)
 {
 	unsigned long flags;
@@ -439,10 +450,10 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
 	start_report(&flags);
 	pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 	print_tags(get_tag(object), reset_tag(object));
-	object = reset_tag(object);
 	pr_err("\n");
 	print_address_description(object);
 	pr_err("\n");
+	object = reset_tag(object);
 	print_shadow_for_address(object);
 	end_report(&flags);
 }
@@ -479,7 +490,7 @@ void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned lon
 	pr_err("\n");
 
 	if (addr_has_shadow(untagged_addr)) {
-		print_address_description(untagged_addr);
+		print_address_description(tagged_addr);
 		pr_err("\n");
 		print_shadow_for_address(info.first_bad_addr);
 	} else {
diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 0e987c9ca052..05a11f1cfff7 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -161,3 +161,89 @@ void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
 	kasan_poison_shadow((void *)addr, size, tag);
 }
 EXPORT_SYMBOL(__hwasan_tag_memory);
+
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+void kasan_set_free_info(struct kmem_cache *cache,
+		void *object, u8 tag)
+{
+	struct kasan_alloc_meta *alloc_meta;
+	struct extra_free_info *free_info;
+	u8 idx;
+
+	alloc_meta = get_alloc_info(cache, object);
+	free_info = &alloc_meta->free_info;
+
+	if (free_info->free_track_tail == 0)
+		free_info->free_track_tail = KASAN_EXTRA_FREE_INFO_COUNT;
+	else
+		free_info->free_track_tail -= 1;
+
+	idx = free_info->free_track_tail;
+	free_info->free_pointer_tag[idx] = tag;
+
+	if (idx == KASAN_EXTRA_FREE_INFO_COUNT)
+		kasan_set_track(&alloc_meta->free_track, GFP_NOWAIT);
+	else
+		kasan_set_track(&free_info->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;
+	struct extra_free_info *free_info;
+	int idx, i;
+
+	alloc_meta = get_alloc_info(cache, object);
+	free_info = &alloc_meta->free_info;
+
+	for (i = 0; i < KASAN_TOTAL_FREE_INFO_COUNT; i++) {
+		idx = free_info->free_track_tail + i;
+		if (idx >= KASAN_TOTAL_FREE_INFO_COUNT)
+			idx -= KASAN_TOTAL_FREE_INFO_COUNT;
+
+		if (free_info->free_pointer_tag[idx] == tag) {
+			if (idx == KASAN_EXTRA_FREE_INFO_COUNT)
+				return &alloc_meta->free_track;
+			else
+				return &free_info->free_track[idx];
+		}
+	}
+	if (free_info->free_track_tail == KASAN_EXTRA_FREE_INFO_COUNT)
+		return &alloc_meta->free_track;
+	else
+		return &free_info->free_track[free_info->free_track_tail];
+}
+
+char *kasan_get_corruption_type(void *addr)
+{
+	struct kasan_alloc_meta *alloc_meta;
+	struct extra_free_info *free_info;
+	struct page *page;
+	struct kmem_cache *cache;
+	void *object;
+	u8 tag;
+	int idx, i;
+
+	tag = get_tag(addr);
+	addr = reset_tag(addr);
+	page = addr_to_page(addr);
+	if (page && PageSlab(page)) {
+		cache = page->slab_cache;
+		object = nearest_obj(cache, page, addr);
+		alloc_meta = get_alloc_info(cache, object);
+		free_info = &alloc_meta->free_info;
+
+		for (i = 0; i < KASAN_TOTAL_FREE_INFO_COUNT; i++) {
+			idx = free_info->free_track_tail + i;
+			if (idx >= KASAN_TOTAL_FREE_INFO_COUNT)
+				idx -= KASAN_TOTAL_FREE_INFO_COUNT;
+
+			if (free_info->free_pointer_tag[idx] == tag)
+				return "use-after-free";
+		}
+		return "out-of-bounds";
+	}
+	return "invalid-access";
+}
+#endif
diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c
index 8eaf5f722271..6d8cdb91c4b6 100644
--- a/mm/kasan/tags_report.c
+++ b/mm/kasan/tags_report.c
@@ -36,7 +36,10 @@
 
 const char *get_bug_type(struct kasan_access_info *info)
 {
-	return "invalid-access";
+	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS_IDENTIFY))
+		return(kasan_get_corruption_type((void *)info->access_addr));
+	else
+		return "invalid-access";
 }
 
 void *find_first_bad_addr(void *addr, size_t size)
-- 
2.18.0




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