From: Ethan Graham <ethangraham@google.com>
Introduce a new helper function, kasan_poison_range(), to encapsulate
the logic for poisoning an arbitrary memory range of a given size, and
expose it publically in <include/linux/kasan.h>.
This is a preparatory change for the upcoming KFuzzTest patches, which
requires the ability to poison the inter-region padding in its input
buffers.
No functional change to any other subsystem is intended by this commit.
Signed-off-by: Ethan Graham <ethangraham@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
---
PR v1:
- Enforce KASAN_GRANULE_SIZE alignment for the end of the range in
kasan_poison_range(), and return -EINVAL when this isn't respected.
---
---
include/linux/kasan.h | 11 +++++++++++
mm/kasan/shadow.c | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 890011071f2b..cd6cdf732378 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -102,6 +102,16 @@ static inline bool kasan_has_integrated_init(void)
}
#ifdef CONFIG_KASAN
+
+/**
+ * kasan_poison_range - poison the memory range [@addr, @addr + @size)
+ *
+ * The exact behavior is subject to alignment with KASAN_GRANULE_SIZE, defined
+ * in <mm/kasan/kasan.h>: if @start is unaligned, the initial partial granule
+ * at the beginning of the range is only poisoned if CONFIG_KASAN_GENERIC=y.
+ */
+int kasan_poison_range(const void *addr, size_t size);
+
void __kasan_unpoison_range(const void *addr, size_t size);
static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
{
@@ -402,6 +412,7 @@ static __always_inline bool kasan_check_byte(const void *addr)
#else /* CONFIG_KASAN */
+static inline int kasan_poison_range(const void *start, size_t size) { 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) {}
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index d2c70cd2afb1..7faed02264f2 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -147,6 +147,40 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
}
EXPORT_SYMBOL_GPL(kasan_poison);
+int kasan_poison_range(const void *addr, size_t size)
+{
+ uintptr_t start_addr = (uintptr_t)addr;
+ uintptr_t head_granule_start;
+ uintptr_t poison_body_start;
+ uintptr_t poison_body_end;
+ size_t head_prefix_size;
+ uintptr_t end_addr;
+
+ if ((start_addr + size) % KASAN_GRANULE_SIZE)
+ return -EINVAL;
+
+ end_addr = ALIGN_DOWN(start_addr + size, KASAN_GRANULE_SIZE);
+ if (start_addr >= end_addr)
+ return -EINVAL;
+
+ head_granule_start = ALIGN_DOWN(start_addr, KASAN_GRANULE_SIZE);
+ head_prefix_size = start_addr - head_granule_start;
+
+ if (IS_ENABLED(CONFIG_KASAN_GENERIC) && head_prefix_size > 0)
+ kasan_poison_last_granule((void *)head_granule_start,
+ head_prefix_size);
+
+ poison_body_start = ALIGN(start_addr, KASAN_GRANULE_SIZE);
+ poison_body_end = ALIGN_DOWN(end_addr, KASAN_GRANULE_SIZE);
+
+ if (poison_body_start < poison_body_end)
+ kasan_poison((void *)poison_body_start,
+ poison_body_end - poison_body_start,
+ KASAN_SLAB_REDZONE, false);
+ return 0;
+}
+EXPORT_SYMBOL(kasan_poison_range);
+
#ifdef CONFIG_KASAN_GENERIC
void kasan_poison_last_granule(const void *addr, size_t size)
{
--
2.51.0.470.ga7dc726c21-googOn Fri, Sep 19, 2025 at 4:58 PM Ethan Graham <ethan.w.s.graham@gmail.com> wrote:
>
> From: Ethan Graham <ethangraham@google.com>
>
> Introduce a new helper function, kasan_poison_range(), to encapsulate
> the logic for poisoning an arbitrary memory range of a given size, and
> expose it publically in <include/linux/kasan.h>.
>
> This is a preparatory change for the upcoming KFuzzTest patches, which
> requires the ability to poison the inter-region padding in its input
> buffers.
>
> No functional change to any other subsystem is intended by this commit.
>
> Signed-off-by: Ethan Graham <ethangraham@google.com>
> Reviewed-by: Alexander Potapenko <glider@google.com>
>
> ---
> PR v1:
> - Enforce KASAN_GRANULE_SIZE alignment for the end of the range in
> kasan_poison_range(), and return -EINVAL when this isn't respected.
> ---
> ---
> include/linux/kasan.h | 11 +++++++++++
> mm/kasan/shadow.c | 34 ++++++++++++++++++++++++++++++++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 890011071f2b..cd6cdf732378 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -102,6 +102,16 @@ static inline bool kasan_has_integrated_init(void)
> }
>
> #ifdef CONFIG_KASAN
> +
> +/**
> + * kasan_poison_range - poison the memory range [@addr, @addr + @size)
> + *
> + * The exact behavior is subject to alignment with KASAN_GRANULE_SIZE, defined
> + * in <mm/kasan/kasan.h>: if @start is unaligned, the initial partial granule
> + * at the beginning of the range is only poisoned if CONFIG_KASAN_GENERIC=y.
> + */
> +int kasan_poison_range(const void *addr, size_t size);
> +
> void __kasan_unpoison_range(const void *addr, size_t size);
> static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
> {
> @@ -402,6 +412,7 @@ static __always_inline bool kasan_check_byte(const void *addr)
>
> #else /* CONFIG_KASAN */
>
> +static inline int kasan_poison_range(const void *start, size_t size) { 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) {}
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index d2c70cd2afb1..7faed02264f2 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -147,6 +147,40 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init)
> }
> EXPORT_SYMBOL_GPL(kasan_poison);
>
> +int kasan_poison_range(const void *addr, size_t size)
This should go into common.c, otherwise this won't be built with the
HW_TAGS mode enabled.
Also, you need a wrapper with a kasan_enabled() check; see how
kasan_unpoison_range() is defined.
> +{
> + uintptr_t start_addr = (uintptr_t)addr;
> + uintptr_t head_granule_start;
> + uintptr_t poison_body_start;
> + uintptr_t poison_body_end;
> + size_t head_prefix_size;
> + uintptr_t end_addr;
> +
> + if ((start_addr + size) % KASAN_GRANULE_SIZE)
> + return -EINVAL;
Other similar KASAN functions do a WARN_ON(bad alignment). I think
printing a warning is fair for this to force the caller to enforce
proper alignment.
> +
> + end_addr = ALIGN_DOWN(start_addr + size, KASAN_GRANULE_SIZE);
I don't think we need to ALIGN_DOWN(): we already checked that
(start_addr + size) % KASAN_GRANULE_SIZE == 0.
> + if (start_addr >= end_addr)
> + return -EINVAL;
Can also do a WARN_ON().
> +
> + head_granule_start = ALIGN_DOWN(start_addr, KASAN_GRANULE_SIZE);
> + head_prefix_size = start_addr - head_granule_start;
> +
> + if (IS_ENABLED(CONFIG_KASAN_GENERIC) && head_prefix_size > 0)
> + kasan_poison_last_granule((void *)head_granule_start,
> + head_prefix_size);
Let's rename kasan_poison_last_granule() to kasan_poison_granule()
then. Here the granule being poisoned is not the last one.
> +
> + poison_body_start = ALIGN(start_addr, KASAN_GRANULE_SIZE);
> + poison_body_end = ALIGN_DOWN(end_addr, KASAN_GRANULE_SIZE);
end_addr is already aligned.
> +
> + if (poison_body_start < poison_body_end)
> + kasan_poison((void *)poison_body_start,
> + poison_body_end - poison_body_start,
> + KASAN_SLAB_REDZONE, false);
> + return 0;
> +}
> +EXPORT_SYMBOL(kasan_poison_range);
> +
> #ifdef CONFIG_KASAN_GENERIC
> void kasan_poison_last_granule(const void *addr, size_t size)
> {
> --
> 2.51.0.470.ga7dc726c21-goog
>
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