[PATCH v4 3/3] kasan: add memory corruption identification support for hardware tag-based mode

[Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>]

Add memory corruption identification support for hardware tag-based
mode. We store one old free pointer tag and free backtrace instead
of five because hardware tag-based kasan only has 16 different tags.

If we store as many stacks as SW tag-based kasan does(5 stacks),
there is high probability to find the same tag in the stacks when
out-of-bound issues happened and we will mistake out-of-bound
issue for use-after-free.

Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Suggested-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 lib/Kconfig.kasan | 2 +-
 mm/kasan/kasan.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index fdb4a08dba83..1e2d10f86011 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -169,7 +169,7 @@ config KASAN_STACK
 
 config KASAN_TAGS_IDENTIFY
 	bool "Enable memory corruption identification"
-	depends on KASAN_SW_TAGS
+	depends on KASAN_SW_TAGS || KASAN_HW_TAGS
 	help
 	  This option enables best-effort identification of bug type
 	  (use-after-free or out-of-bounds) at the cost of increased
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 952df2db7fdd..f58672f6029a 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -153,7 +153,7 @@ struct kasan_track {
 	depot_stack_handle_t stack;
 };
 
-#ifdef CONFIG_KASAN_TAGS_IDENTIFY
+#if defined(CONFIG_KASAN_TAGS_IDENTIFY) && defined(CONFIG_KASAN_SW_TAGS)
 #define KASAN_NR_FREE_STACKS 5
 #else
 #define KASAN_NR_FREE_STACKS 1
-- 
2.18.0