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From:   andrey.konovalov@linux.dev
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Florian Mayer <fmayer@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH mm v3 15/34] kasan: only define kasan_never_merge for Generic mode
Date:   Mon,  5 Sep 2022 23:05:30 +0200
Message-Id: <81ed01f29ff3443580b7e2fe362a8b47b1e8006d.1662411799.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

KASAN prevents merging of slab caches whose objects have per-object
metadata stored in redzones.

As now only the Generic mode uses per-object metadata, define
kasan_never_merge() only for this mode.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/kasan.h | 18 ++++++------------
 mm/kasan/common.c     |  8 --------
 mm/kasan/generic.c    |  8 ++++++++
 3 files changed, 14 insertions(+), 20 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 027df7599573..9743d4b3a918 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -103,14 +103,6 @@ struct kasan_cache {
 	bool is_kmalloc;
 };
 
-slab_flags_t __kasan_never_merge(void);
-static __always_inline slab_flags_t kasan_never_merge(void)
-{
-	if (kasan_enabled())
-		return __kasan_never_merge();
-	return 0;
-}
-
 void __kasan_unpoison_range(const void *addr, size_t size);
 static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
 {
@@ -261,10 +253,6 @@ static __always_inline bool kasan_check_byte(const void *addr)
 
 #else /* CONFIG_KASAN */
 
-static inline slab_flags_t kasan_never_merge(void)
-{
-	return 0;
-}
 static inline void kasan_unpoison_range(const void *address, size_t size) {}
 static inline void kasan_poison_pages(struct page *page, unsigned int order,
 				      bool init) {}
@@ -325,6 +313,7 @@ static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
 #ifdef CONFIG_KASAN_GENERIC
 
 size_t kasan_metadata_size(struct kmem_cache *cache);
+slab_flags_t kasan_never_merge(void);
 
 void kasan_cache_shrink(struct kmem_cache *cache);
 void kasan_cache_shutdown(struct kmem_cache *cache);
@@ -338,6 +327,11 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache)
 {
 	return 0;
 }
+/* And thus nothing prevents cache merging. */
+static inline slab_flags_t kasan_never_merge(void)
+{
+	return 0;
+}
 
 static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
 static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 7c79c560315d..c2690e938030 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -88,14 +88,6 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
 }
 #endif /* CONFIG_KASAN_STACK */
 
-/* Only allow cache merging when no per-object metadata is present. */
-slab_flags_t __kasan_never_merge(void)
-{
-	if (kasan_requires_meta())
-		return SLAB_KASAN;
-	return 0;
-}
-
 void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init)
 {
 	u8 tag;
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 806ab92032c3..25333bf3c99f 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -328,6 +328,14 @@ DEFINE_ASAN_SET_SHADOW(f3);
 DEFINE_ASAN_SET_SHADOW(f5);
 DEFINE_ASAN_SET_SHADOW(f8);
 
+/* Only allow cache merging when no per-object metadata is present. */
+slab_flags_t kasan_never_merge(void)
+{
+	if (!kasan_requires_meta())
+		return 0;
+	return SLAB_KASAN;
+}
+
 /*
  * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
  * For larger allocations larger redzones are used.
-- 
2.25.1