Re: [PATCH 05/12] kasan: unify large kfree checks

[Marco Elver]

On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> Unify checks in kasan_kfree_large() and in kasan_slab_free_mempool()
> for large allocations as it's done for small kfree() allocations.
> 
> With this change, kasan_slab_free_mempool() starts checking that the
> first byte of the memory that's being freed is accessible.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
>  include/linux/kasan.h | 16 ++++++++--------
>  mm/kasan/common.c     | 36 ++++++++++++++++++++++++++----------
>  2 files changed, 34 insertions(+), 18 deletions(-)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 2d5de4092185..d53ea3c047bc 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -200,6 +200,13 @@ static __always_inline bool kasan_slab_free(struct kmem_cache *s, void *object)
>  	return false;
>  }
>  
> +void __kasan_kfree_large(void *ptr, unsigned long ip);
> +static __always_inline void kasan_kfree_large(void *ptr)
> +{
> +	if (kasan_enabled())
> +		__kasan_kfree_large(ptr, _RET_IP_);
> +}
> +
>  void __kasan_slab_free_mempool(void *ptr, unsigned long ip);
>  static __always_inline void kasan_slab_free_mempool(void *ptr)
>  {
> @@ -247,13 +254,6 @@ static __always_inline void * __must_check kasan_krealloc(const void *object,
>  	return (void *)object;
>  }
>  
> -void __kasan_kfree_large(void *ptr, unsigned long ip);
> -static __always_inline void kasan_kfree_large(void *ptr)
> -{
> -	if (kasan_enabled())
> -		__kasan_kfree_large(ptr, _RET_IP_);
> -}
> -
>  /*
>   * Unlike kasan_check_read/write(), kasan_check_byte() is performed even for
>   * the hardware tag-based mode that doesn't rely on compiler instrumentation.
> @@ -302,6 +302,7 @@ static inline bool kasan_slab_free(struct kmem_cache *s, void *object)
>  {
>  	return false;
>  }
> +static inline void kasan_kfree_large(void *ptr) {}
>  static inline void kasan_slab_free_mempool(void *ptr) {}
>  static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
>  				   gfp_t flags)
> @@ -322,7 +323,6 @@ static inline void *kasan_krealloc(const void *object, size_t new_size,
>  {
>  	return (void *)object;
>  }
> -static inline void kasan_kfree_large(void *ptr) {}
>  static inline bool kasan_check_byte(const void *address)
>  {
>  	return true;
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 086bb77292b6..9c64a00bbf9c 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -364,6 +364,31 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
>  	return ____kasan_slab_free(cache, object, ip, true);
>  }
>  
> +static bool ____kasan_kfree_large(void *ptr, unsigned long ip)
> +{
> +	if (ptr != page_address(virt_to_head_page(ptr))) {
> +		kasan_report_invalid_free(ptr, ip);
> +		return true;
> +	}
> +
> +	if (!kasan_byte_accessible(ptr)) {
> +		kasan_report_invalid_free(ptr, ip);
> +		return true;
> +	}
> +
> +	/*
> +	 * The object will be poisoned by kasan_free_pages() or
> +	 * kasan_slab_free_mempool().
> +	 */
> +
> +	return false;
> +}
> +
> +void __kasan_kfree_large(void *ptr, unsigned long ip)
> +{
> +	____kasan_kfree_large(ptr, ip);
> +}
> +
>  void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
>  {
>  	struct page *page;
> @@ -377,10 +402,8 @@ void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
>  	 * KMALLOC_MAX_SIZE, and kmalloc falls back onto page_alloc.
>  	 */
>  	if (unlikely(!PageSlab(page))) {
> -		if (ptr != page_address(page)) {
> -			kasan_report_invalid_free(ptr, ip);
> +		if (____kasan_kfree_large(ptr, ip))
>  			return;
> -		}
>  		kasan_poison(ptr, page_size(page), KASAN_FREE_PAGE);
>  	} else {
>  		____kasan_slab_free(page->slab_cache, ptr, ip, false);
> @@ -539,13 +562,6 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
>  		return ____kasan_kmalloc(page->slab_cache, object, size, flags);
>  }
>  
> -void __kasan_kfree_large(void *ptr, unsigned long ip)
> -{
> -	if (ptr != page_address(virt_to_head_page(ptr)))
> -		kasan_report_invalid_free(ptr, ip);
> -	/* The object will be poisoned by kasan_free_pages(). */
> -}
> -
>  bool __kasan_check_byte(const void *address, unsigned long ip)
>  {
>  	if (!kasan_byte_accessible(address)) {
> -- 
> 2.30.0.365.g02bc693789-goog
>