From: Yee Lee <[email protected]>
Issue: In SLUB debug, hwtag kasan_unpoison() would overwrite the redzone
in those objects with unaligned size.
The first patch Introduces slub_debug_enable_unlikely() to check
the state of debug mode.
The second patch Adds memzero_explict() to separate the initialization for
such condition. The new code path is executed about 1.1% during nromal
booting process. The penalty is acceptable since it only works in debug
mode.
=============
Exp: QEMUv5.2(+mte)/SLUB_debug mode
code path exec : 941/80854 (1.1%)
Changed since v5:
- Fix format
Changed since v4:
- Introduce slub_debug_enable_unlikly() to check the debug state.
- Include "slab.h" and Add slub_debug_enable_unlikly() to lead
the condition statement.
- Add comment block about this new code path in source code.
Changed since v3:
- Apply IS_ENABLED to wrap codes under SLUB debug mode.
- Replace memset() by memzero_explict().
---
Marco Elver (1):
mm: introduce helper to check slub_debug_enabled
Yee Lee (1):
kasan: Add memzero int for unaligned size at DEBUG
mm/kasan/kasan.h | 12 ++++++++++++
mm/slab.h | 15 +++++++++++----
2 files changed, 23 insertions(+), 4 deletions(-)
--
2.18.0
From: Yee Lee <[email protected]>
Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite
the redzone of object with unaligned size.
An additional memzero_explicit() path is added to replacing init by
hwtag instruction for those unaligned size at SLUB debug mode.
The penalty is acceptable since they are only enabled in debug mode,
not production builds. A block of comment is added for explanation.
Signed-off-by: Yee Lee <[email protected]>
Suggested-by: Marco Elver <[email protected]>
Suggested-by: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Andrew Morton <[email protected]>
---
mm/kasan/kasan.h | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 98e3059bfea4..a9d837197302 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -9,6 +9,7 @@
#ifdef CONFIG_KASAN_HW_TAGS
#include <linux/static_key.h>
+#include "../slab.h"
DECLARE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
extern bool kasan_flag_async __ro_after_init;
@@ -387,6 +388,17 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
return;
+ /*
+ * Explicitly initialize the memory with the precise object size to
+ * avoid overwriting the SLAB redzone. This disables initialization in
+ * the arch code and may thus lead to performance penalty. The penalty
+ * is accepted since SLAB redzones aren't enabled in production builds.
+ */
+ if (slub_debug_enabled_unlikely() &&
+ init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
+ init = false;
+ memzero_explicit((void *)addr, size);
+ }
size = round_up(size, KASAN_GRANULE_SIZE);
hw_set_mem_tag_range((void *)addr, size, tag, init);
--
2.18.0