kasan: add memory corruption identification for software tag-based mode

Add memory corruption identification at bug report for software tag-based
mode.  The report shows 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".

[aryabinin@virtuozzo.com: simplify & clenup code]
  Link: https://lkml.kernel.org/r/3318f9d7-a760-3cc8-b700-f06108ae745f@virtuozzo.com]
Link: http://lkml.kernel.org/r/20190821180332.11450-1-aryabinin@virtuozzo.com
Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.kasan

@@ -134,6 +134,14 @@ 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.
+
 config TEST_KASAN
 	tristate "Module for testing KASAN for bug detection"
 	depends on m && KASAN

mm/kasan/common.c

@@ -304,7 +304,6 @@ 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);
 	return (void *)object + cache->kasan_info.alloc_meta_offset;
 }
 
@@ -315,6 +314,24 @@ 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;
@@ -452,7 +469,8 @@ 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);
+	kasan_set_free_info(cache, object, tag);
+
 	quarantine_put(get_free_info(cache, object), cache);
 
 	return IS_ENABLED(CONFIG_KASAN_GENERIC);

mm/kasan/kasan.h

@@ -95,9 +95,19 @@ struct kasan_track {
 	depot_stack_handle_t stack;
 };
 
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+#define KASAN_NR_FREE_STACKS 5
+#else
+#define KASAN_NR_FREE_STACKS 1
+#endif
+
 struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
-	struct kasan_track free_track;
+	struct kasan_track free_track[KASAN_NR_FREE_STACKS];
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+	u8 free_pointer_tag[KASAN_NR_FREE_STACKS];
+	u8 free_track_idx;
+#endif
 };
 
 struct qlist_node {
@@ -146,6 +156,8 @@ 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 *kasan_addr_to_page(const void *addr);
+
 #if defined(CONFIG_KASAN_GENERIC) && \
 	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);

mm/kasan/report.c

@@ -111,7 +111,7 @@ static void print_track(struct kasan_track *track, const char *prefix)
 	}
 }
 
-static struct page *addr_to_page(const void *addr)
+struct page *kasan_addr_to_page(const void *addr)
 {
 	if ((addr >= (void *)PAGE_OFFSET) &&
 			(addr < high_memory))
@@ -151,15 +151,38 @@ 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)
+				const void *addr, u8 tag)
 {
 	struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 
 	if (cache->flags & SLAB_KASAN) {
+		struct kasan_track *free_track;
+
 		print_track(&alloc_info->alloc_track, "Allocated");
 		pr_err("\n");
-		print_track(&alloc_info->free_track, "Freed");
+		free_track = kasan_get_free_track(cache, object, tag);
+		print_track(free_track, "Freed");
 		pr_err("\n");
 	}
 
@@ -344,9 +367,9 @@ 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 *addr, u8 tag)
 {
-	struct page *page = addr_to_page(addr);
+	struct page *page = kasan_addr_to_page(addr);
 
 	dump_stack();
 	pr_err("\n");
@@ -355,7 +378,7 @@ static void print_address_description(void *addr)
 		struct kmem_cache *cache = page->slab_cache;
 		void *object = nearest_obj(cache, page,	addr);
 
-		describe_object(cache, object, addr);
+		describe_object(cache, object, addr, tag);
 	}
 
 	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
@@ -435,13 +458,14 @@ static bool report_enabled(void)
 void kasan_report_invalid_free(void *object, unsigned long ip)
 {
 	unsigned long flags;
+	u8 tag = get_tag(object);
 
+	object = reset_tag(object);
 	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);
+	print_tags(tag, object);
 	pr_err("\n");
-	print_address_description(object);
+	print_address_description(object, tag);
 	pr_err("\n");
 	print_shadow_for_address(object);
 	end_report(&flags);
@@ -479,7 +503,7 @@ 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(untagged_addr, get_tag(tagged_addr));
 		pr_err("\n");
 		print_shadow_for_address(info.first_bad_addr);
 	} else {

mm/kasan/tags_report.c

@@ -36,6 +36,30 @@
 
 const char *get_bug_type(struct kasan_access_info *info)
 {
+#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
+	struct kasan_alloc_meta *alloc_meta;
+	struct kmem_cache *cache;
+	struct page *page;
+	const void *addr;
+	void *object;
+	u8 tag;
+	int i;
+
+	tag = get_tag(info->access_addr);
+	addr = reset_tag(info->access_addr);
+	page = kasan_addr_to_page(addr);
+	if (page && PageSlab(page)) {
+		cache = page->slab_cache;
+		object = nearest_obj(cache, page, (void *)addr);
+		alloc_meta = get_alloc_info(cache, object);
+
+		for (i = 0; i < KASAN_NR_FREE_STACKS; i++)
+			if (alloc_meta->free_pointer_tag[i] == tag)
+				return "use-after-free";
+		return "out-of-bounds";
+	}
+
+#endif
 	return "invalid-access";
 }