Re: [PATCH v2] ARM/dma-mapping: use kvcalloc for fallback memory allocation need

[Deepak R Varma <drv@mailo.com>]

On Tue, Dec 20, 2022 at 07:46:32PM +0530, Deepak R Varma wrote:
> Current conditional determination of whether to use kzalloc or vzalloc
> has known issues such as "indefinite retry" when less than PAGE_SIZE
> memory is needed, but is unavailable. This LWN article [1] describes
> these issues in greater detail. Use helper function kvcalloc() instead
> which is more efficient in terms of performance and security.
>
>  	[1] https://lwn.net/Articles/711653/
>
> This patch proposal is based on following Coccinelle warning using the
> kvmalloc.cocci semantic patch.
> 	arch/arm/mm/dma-mapping.c:858:28-29: WARNING opportunity for kvmalloc
>
> The semantic patch suggests using kvzalloc() helper function, however,
> this patch proposes to use kvcalloc instead. kvcalloc() helper function
> uses 2-factor argument form which is better from a security perspective
> as described in the following KSPP project commit.
>
> 	Commit 4e3fd7217105 ("wireguard: ratelimiter: use kvcalloc() instead of kvzalloc()")
>
> Signed-off-by: Deepak R Varma <drv@mailo.com>

Hello,
May I please request a review and feedback on this patch proposal?

Thank you,
./drv

> ---
>
> Changes in v2:
>    1. Update patch subject to use kvcalloc
>    2. Use kvcalloc instead of kvzalloc helper function. Revise the patch
>       proposal and the patch description accordingly.
>
>
>  arch/arm/mm/dma-mapping.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index c135f6e37a00..35092ecd30e1 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -851,14 +851,10 @@ static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
>  {
>  	struct page **pages;
>  	int count = size >> PAGE_SHIFT;
> -	int array_size = count * sizeof(struct page *);
>  	int i = 0;
>  	int order_idx = 0;
>
> -	if (array_size <= PAGE_SIZE)
> -		pages = kzalloc(array_size, GFP_KERNEL);
> -	else
> -		pages = vzalloc(array_size);
> +	pages = kvcalloc(count, sizeof(struct page *), GFP_KERNEL);
>  	if (!pages)
>  		return NULL;
>
> --
> 2.34.1
>



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