Re: [PATCH 03/12] kasan: optimize large kmalloc poisoning

[Marco Elver]

On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> Similarly to kasan_kmalloc(), kasan_kmalloc_large() doesn't need
> to unpoison the object as it as already unpoisoned by alloc_pages()
> (or by ksize() for krealloc()).
> 
> This patch changes kasan_kmalloc_large() to only poison the redzone.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
>  mm/kasan/common.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 128cb330ca73..a7eb553c8e91 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -494,7 +494,6 @@ EXPORT_SYMBOL(__kasan_kmalloc);
>  void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
>  						gfp_t flags)
>  {
> -	struct page *page;
>  	unsigned long redzone_start;
>  	unsigned long redzone_end;
>  
> @@ -504,12 +503,23 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
>  	if (unlikely(ptr == NULL))
>  		return NULL;
>  
> -	page = virt_to_page(ptr);
> +	/*
> +	 * The object has already been unpoisoned by kasan_alloc_pages() for
> +	 * alloc_pages() or by ksize() for krealloc().
> +	 */
> +
> +	/*
> +	 * The redzone has byte-level precision for the generic mode.
> +	 * Partially poison the last object granule to cover the unaligned
> +	 * part of the redzone.
> +	 */
> +	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +		kasan_poison_last_granule(ptr, size);
> +
> +	/* Poison the aligned part of the redzone. */
>  	redzone_start = round_up((unsigned long)(ptr + size),
>  				KASAN_GRANULE_SIZE);
> -	redzone_end = (unsigned long)ptr + page_size(page);
> -
> -	kasan_unpoison(ptr, size);
> +	redzone_end = (unsigned long)ptr + page_size(virt_to_page(ptr));
>  	kasan_poison((void *)redzone_start, redzone_end - redzone_start,
>  		     KASAN_PAGE_REDZONE);
>  
> -- 
> 2.30.0.365.g02bc693789-goog
>