Re: [PATCH v2] ARM: dma-mapping: always clear allocated buffers

[YueHaibing]

+CC  Christoph Hellwig <hch@xxxxxxxxxxxxx>

On 2018/7/25 15:07, YueHaibing wrote:
> Sean Wang reported dma_zalloc_coherent doesn't work as expect on his
> armv7,the allocated mem is not zeroed.The reason is __alloc_from_pool
> doesn't honor __GFP_ZERO.
> 
> As commit 6829e274a623 ("arm64: dma-mapping: always clear allocated buffers")
> has pointed out,buffers allocated by dma_alloc_coherent() are always zeroed
> on most architectures. some drivers rely on this 'feature'. Allocated buffer
> might be also exposed to userspace with dma_mmap() call,so clearing it is
> desired from security point of view to avoid exposing random memory to userspace.
> 
> This patch unifies dma_alloc_coherent() behavior on ARM architecture with other
> implementations by unconditionally zeroing allocated buffer.Also to fix
> dma_zalloc_coherent behavior.
> 
> Reported-by: Sean Wang <sean.wang@xxxxxxxxxxxx>
> Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
> Reviewed-by: zhong jiang <zhongjiang@xxxxxxxxxx>
> ---
> v2: reference more argument from arm64 commit as Christoph suggested
> ---
>  arch/arm/mm/dma-mapping.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 6656647..cf5882f 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -564,6 +564,7 @@ static void *__alloc_from_pool(size_t size, struct page **ret_page)
>  
>  		*ret_page = phys_to_page(phys);
>  		ptr = (void *)val;
> +		memset(ptr, 0, size);
>  	}
>  
>  	return ptr;
>