[PATCH 0/3] kasan: common: cleanups and deduplication

[PATCH 0/3] kasan: common: cleanups and deduplication

[Igor Putko]

This patch series refactors KASAN common code to improve readability 
and maintainability.

Specifically, it:
- Introduces a helper for quarantine reduction to eliminate boilerplate.
- Utilizes the standard ALIGN_DOWN macro instead of manual bitwise logic.
- Replaces a magic number with the KASAN_TAG_KERNEL definition.

Igor Putko (3):
  kasan: deduplicate quarantine reduction logic
  kasan: common: use ALIGN_DOWN macro for stack alignment
  kasan: common: replace magic number with KASAN_TAG_KERNEL

 mm/kasan/common.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

-- 
2.47.3

[PATCH 1/3] kasan: deduplicate quarantine reduction logic

[Igor Putko]

Multiple allocation functions share the exact same conditional logic for
reducing the KASAN quarantine size based on gfp flags.
Introduce the kasan_quarantine_reduce_cond() helper to eliminate this
boilerplate from the slab, kmalloc, kmalloc_large, and krealloc paths.

Signed-off-by: Igor Putko <igorpetindev@gmail.com>
---
 mm/kasan/common.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index b7d05c2a6..34aa0fdce 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -340,14 +340,19 @@ static inline void unpoison_slab_object(struct kmem_cache *cache, void *object,
 		kasan_save_alloc_info(cache, object, flags);
 }
 
+static inline void kasan_quarantine_reduce_cond(gfp_t flags)
+{
+	if (gfpflags_allow_blocking(flags))
+		kasan_quarantine_reduce();
+}
+
 void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
 					void *object, gfp_t flags, bool init)
 {
 	u8 tag;
 	void *tagged_object;
 
-	if (gfpflags_allow_blocking(flags))
-		kasan_quarantine_reduce();
+	kasan_quarantine_reduce_cond(flags);
 
 	if (unlikely(object == NULL))
 		return NULL;
@@ -402,8 +407,7 @@ static inline void poison_kmalloc_redzone(struct kmem_cache *cache,
 void * __must_check __kasan_kmalloc(struct kmem_cache *cache, const void *object,
 					size_t size, gfp_t flags)
 {
-	if (gfpflags_allow_blocking(flags))
-		kasan_quarantine_reduce();
+	kasan_quarantine_reduce_cond(flags);
 
 	if (unlikely(object == NULL))
 		return NULL;
@@ -443,8 +447,7 @@ static inline void poison_kmalloc_large_redzone(const void *ptr, size_t size,
 void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
 						gfp_t flags)
 {
-	if (gfpflags_allow_blocking(flags))
-		kasan_quarantine_reduce();
+	kasan_quarantine_reduce_cond(flags);
 
 	if (unlikely(ptr == NULL))
 		return NULL;
@@ -460,8 +463,7 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
 {
 	struct slab *slab;
 
-	if (gfpflags_allow_blocking(flags))
-		kasan_quarantine_reduce();
+	kasan_quarantine_reduce_cond(flags);
 
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return (void *)object;
-- 
2.47.3

Re: [PATCH 1/3] kasan: deduplicate quarantine reduction logic

[Andrey Konovalov]

On Sat, Jul 4, 2026 at 11:20 AM Igor Putko <igorpetindev@gmail.com> wrote:
>
> Multiple allocation functions share the exact same conditional logic for
> reducing the KASAN quarantine size based on gfp flags.
> Introduce the kasan_quarantine_reduce_cond() helper to eliminate this
> boilerplate from the slab, kmalloc, kmalloc_large, and krealloc paths.
>
> Signed-off-by: Igor Putko <igorpetindev@gmail.com>
> ---
>  mm/kasan/common.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index b7d05c2a6..34aa0fdce 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -340,14 +340,19 @@ static inline void unpoison_slab_object(struct kmem_cache *cache, void *object,
>                 kasan_save_alloc_info(cache, object, flags);
>  }
>
> +static inline void kasan_quarantine_reduce_cond(gfp_t flags)
> +{
> +       if (gfpflags_allow_blocking(flags))
> +               kasan_quarantine_reduce();
> +}

Not sure about this change: it's hiding the condition for when
kasan_quarantine_reduce() gets to execute and does not really improve
the code readability otherwise.






> +
>  void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
>                                         void *object, gfp_t flags, bool init)
>  {
>         u8 tag;
>         void *tagged_object;
>
> -       if (gfpflags_allow_blocking(flags))
> -               kasan_quarantine_reduce();
> +       kasan_quarantine_reduce_cond(flags);
>
>         if (unlikely(object == NULL))
>                 return NULL;
> @@ -402,8 +407,7 @@ static inline void poison_kmalloc_redzone(struct kmem_cache *cache,
>  void * __must_check __kasan_kmalloc(struct kmem_cache *cache, const void *object,
>                                         size_t size, gfp_t flags)
>  {
> -       if (gfpflags_allow_blocking(flags))
> -               kasan_quarantine_reduce();
> +       kasan_quarantine_reduce_cond(flags);
>
>         if (unlikely(object == NULL))
>                 return NULL;
> @@ -443,8 +447,7 @@ static inline void poison_kmalloc_large_redzone(const void *ptr, size_t size,
>  void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
>                                                 gfp_t flags)
>  {
> -       if (gfpflags_allow_blocking(flags))
> -               kasan_quarantine_reduce();
> +       kasan_quarantine_reduce_cond(flags);
>
>         if (unlikely(ptr == NULL))
>                 return NULL;
> @@ -460,8 +463,7 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
>  {
>         struct slab *slab;
>
> -       if (gfpflags_allow_blocking(flags))
> -               kasan_quarantine_reduce();
> +       kasan_quarantine_reduce_cond(flags);
>
>         if (unlikely(object == ZERO_SIZE_PTR))
>                 return (void *)object;
> --
> 2.47.3
>

[PATCH 2/3] kasan: common: use ALIGN_DOWN macro for stack alignment

[Igor Putko]

Replace the manual bitwise alignment logic in
kasan_unpoison_task_stack_below() with the
standard ALIGN_DOWN macro. This improves code
readability and conforms to standard kernel idioms.

Signed-off-by: Igor Putko <igorpetindev@gmail.com>
---
 mm/kasan/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 34aa0fdce..5faf73c8f 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -119,7 +119,7 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
 	 * because this function is called by early resume code which hasn't
 	 * yet set up the percpu register (%gs).
 	 */
-	void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
+	void *base = (void *)ALIGN_DOWN((unsigned long)watermark, THREAD_SIZE);
 
 	kasan_unpoison(base, watermark - base, false);
 }
-- 
2.47.3

Re: [PATCH 2/3] kasan: common: use ALIGN_DOWN macro for stack alignment

[Andrey Konovalov]

On Sat, Jul 4, 2026 at 11:20 AM Igor Putko <igorpetindev@gmail.com> wrote:
>
> Replace the manual bitwise alignment logic in
> kasan_unpoison_task_stack_below() with the
> standard ALIGN_DOWN macro. This improves code
> readability and conforms to standard kernel idioms.
>
> Signed-off-by: Igor Putko <igorpetindev@gmail.com>
> ---
>  mm/kasan/common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 34aa0fdce..5faf73c8f 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -119,7 +119,7 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
>          * because this function is called by early resume code which hasn't
>          * yet set up the percpu register (%gs).
>          */
> -       void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
> +       void *base = (void *)ALIGN_DOWN((unsigned long)watermark, THREAD_SIZE);
>
>         kasan_unpoison(base, watermark - base, false);
>  }
> --
> 2.47.3
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>

[PATCH 3/3] kasan: common: replace magic number with KASAN_TAG_KERNEL

[Igor Putko]

Replace the literal 0xff in assign_tag()
with KASAN_TAG_KERNEL to eliminate the
magic number and improve code clarity.

Signed-off-by: Igor Putko <igorpetindev@gmail.com>
---
 mm/kasan/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 5faf73c8f..3e9b6b8f5 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -188,7 +188,7 @@ static inline u8 assign_tag(struct kmem_cache *cache,
 					const void *object, bool init)
 {
 	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
-		return 0xff;
+		return KASAN_TAG_KERNEL;
 
 	/*
 	 * If the cache neither has a constructor nor has SLAB_TYPESAFE_BY_RCU
-- 
2.47.3

Re: [PATCH 3/3] kasan: common: replace magic number with KASAN_TAG_KERNEL

[Andrey Konovalov]

On Sat, Jul 4, 2026 at 11:20 AM Igor Putko <igorpetindev@gmail.com> wrote:
>
> Replace the literal 0xff in assign_tag()
> with KASAN_TAG_KERNEL to eliminate the
> magic number and improve code clarity.
>
> Signed-off-by: Igor Putko <igorpetindev@gmail.com>
> ---
>  mm/kasan/common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 5faf73c8f..3e9b6b8f5 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -188,7 +188,7 @@ static inline u8 assign_tag(struct kmem_cache *cache,
>                                         const void *object, bool init)
>  {
>         if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> -               return 0xff;
> +               return KASAN_TAG_KERNEL;

Not sure about this change either: the notion of a tag does no apply
to the Generic mode, so the code uses 0xff in such cases (the second
definition of page_kasan_tag() is another case).



>
>         /*
>          * If the cache neither has a constructor nor has SLAB_TYPESAFE_BY_RCU
> --
> 2.47.3
>