Re: [PATCH v2 10/20] kasan: inline and rename kasan_unpoison_memory
From: Marco Elver
Date: Wed Nov 11 2020 - 12:49:12 EST
On Tue, Nov 10, 2020 at 11:20PM +0100, Andrey Konovalov wrote:
> Currently kasan_unpoison_memory() is used as both an external annotation
> and as an internal memory poisoning helper. Rename external annotation to
> kasan_unpoison_data() and inline the internal helper for hardware
> tag-based mode to avoid undeeded function calls.
I don't understand why this needs to be renamed again. The users of
kasan_unpoison_memory() outweigh those of kasan_unpoison_slab(), of
which there seems to be only 1!
So can't we just get rid of kasan_unpoison_slab() and just open-code it
in mm/mempool.c:kasan_unpoison_element()? That function is already
kasan-prefixed, so we can even place a small comment there (which would
also be an improvement over current interface, since
kasan_unpoison_slab() is not documented and its existence not quite
justified).
> There's the external annotation kasan_unpoison_slab() that is currently
> defined as static inline and uses kasan_unpoison_memory(). With this
> change it's turned into a function call. Overall, this results in the
> same number of calls for hardware tag-based mode as
> kasan_unpoison_memory() is now inlined.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/Ia7c8b659f79209935cbaab3913bf7f082cc43a0e
> ---
> include/linux/kasan.h | 16 ++++++----------
> kernel/fork.c | 2 +-
> mm/kasan/common.c | 10 ++++++++++
> mm/kasan/hw_tags.c | 6 ------
> mm/kasan/kasan.h | 7 +++++++
> mm/slab_common.c | 2 +-
> 6 files changed, 25 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 53c8e8b12fbc..f1a5042ae4fc 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -74,14 +74,15 @@ static inline void kasan_disable_current(void) {}
>
> #ifdef CONFIG_KASAN
>
> -void kasan_unpoison_memory(const void *address, size_t size);
> -
> void kasan_alloc_pages(struct page *page, unsigned int order);
> void kasan_free_pages(struct page *page, unsigned int order);
>
> void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> slab_flags_t *flags);
>
> +void kasan_unpoison_data(const void *address, size_t size);
> +void kasan_unpoison_slab(const void *ptr);
> +
> void kasan_poison_slab(struct page *page);
> void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
> void kasan_poison_object_data(struct kmem_cache *cache, void *object);
> @@ -106,11 +107,6 @@ struct kasan_cache {
> int free_meta_offset;
> };
>
> -size_t __ksize(const void *);
> -static inline void kasan_unpoison_slab(const void *ptr)
> -{
> - kasan_unpoison_memory(ptr, __ksize(ptr));
> -}
> size_t kasan_metadata_size(struct kmem_cache *cache);
>
> bool kasan_save_enable_multi_shot(void);
> @@ -118,8 +114,6 @@ void kasan_restore_multi_shot(bool enabled);
>
> #else /* CONFIG_KASAN */
>
> -static inline void kasan_unpoison_memory(const void *address, size_t size) {}
> -
> static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
> static inline void kasan_free_pages(struct page *page, unsigned int order) {}
>
> @@ -127,6 +121,9 @@ static inline void kasan_cache_create(struct kmem_cache *cache,
> unsigned int *size,
> slab_flags_t *flags) {}
>
> +static inline void kasan_unpoison_data(const void *address, size_t size) { }
> +static inline void kasan_unpoison_slab(const void *ptr) { }
> +
> static inline void kasan_poison_slab(struct page *page) {}
> static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
> void *object) {}
> @@ -166,7 +163,6 @@ static inline bool kasan_slab_free(struct kmem_cache *s, void *object,
> return false;
> }
>
> -static inline void kasan_unpoison_slab(const void *ptr) { }
> static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
>
> #endif /* CONFIG_KASAN */
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 1c905e4290ab..883898487b3f 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -226,7 +226,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
> continue;
>
> /* Mark stack accessible for KASAN. */
> - kasan_unpoison_memory(s->addr, THREAD_SIZE);
> + kasan_unpoison_data(s->addr, THREAD_SIZE);
... this change would become unnecessary.
> /* Clear stale pointers from reused stack. */
> memset(s->addr, 0, THREAD_SIZE);
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index a266b90636a1..4598c1364f19 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -184,6 +184,16 @@ struct kasan_free_meta *kasan_get_free_meta(struct kmem_cache *cache,
> return kasan_reset_tag(object) + cache->kasan_info.free_meta_offset;
> }
>
> +void kasan_unpoison_data(const void *address, size_t size)
> +{
> + kasan_unpoison_memory(address, size);
> +}
> +
> +void kasan_unpoison_slab(const void *ptr)
> +{
> + kasan_unpoison_memory(ptr, __ksize(ptr));
> +}
> +
This function is so simple, I think just open-coding
kasan_unpoison_memory(ptr, __ksize(ptr))
wherever required is much simpler, also bearing in mind the changes that
are coming to the rest of this series.
> void kasan_poison_slab(struct page *page)
> {
> unsigned long i;
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 0303e49904b4..838b29e44e32 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -30,12 +30,6 @@ void kasan_init_hw_tags(void)
> pr_info("KernelAddressSanitizer initialized\n");
> }
>
> -void kasan_unpoison_memory(const void *address, size_t size)
> -{
> - hw_set_mem_tag_range(kasan_reset_tag(address),
> - round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
> -}
> -
> void kasan_set_free_info(struct kmem_cache *cache,
> void *object, u8 tag)
> {
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index ab7314418604..2d3c99125996 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -283,6 +283,12 @@ static inline void kasan_poison_memory(const void *address, size_t size, u8 valu
> round_up(size, KASAN_GRANULE_SIZE), value);
> }
>
> +static inline void kasan_unpoison_memory(const void *address, size_t size)
> +{
> + hw_set_mem_tag_range(kasan_reset_tag(address),
> + round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
> +}
> +
> static inline bool check_invalid_free(void *addr)
> {
> u8 ptr_tag = get_tag(addr);
> @@ -295,6 +301,7 @@ static inline bool check_invalid_free(void *addr)
> #else /* CONFIG_KASAN_HW_TAGS */
>
> void kasan_poison_memory(const void *address, size_t size, u8 value);
> +void kasan_unpoison_memory(const void *address, size_t size);
> bool check_invalid_free(void *addr);
>
> #endif /* CONFIG_KASAN_HW_TAGS */
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 53d0f8bb57ea..f1b0c4a22f08 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1176,7 +1176,7 @@ size_t ksize(const void *objp)
> * We assume that ksize callers could use whole allocated area,
> * so we need to unpoison this area.
> */
> - kasan_unpoison_memory(objp, size);
> + kasan_unpoison_data(objp, size);
... this change would become unnecessary.
Thanks,
-- Marco