[PATCH] arch/arm/mm/dma-mapping.c: fix __alloc_from_pool returning a dirty buffer

[Russell King (Oracle)]

On Fri, Dec 23, 2022 at 11:51:43PM +0100, Igor Klochko wrote:
> Thanks Christoph,
> 
> Added fixes and a changelog.
> This issue is present in all current LTS versions.
> 
> ----
> Buffers allocated by __alloc_from_pool() should be zeroed out as done by other allocators.
> Certain drivers expect a clean buffer and clearing the buffer is beneficial from the security point of view.
> ---
> Fixes: 36d0fd2198da3 (*arm: use genalloc for the atomic pool*)
> Signed-off-by: Igor Klochko <igor.klochko at gmail.com>
> ---
>  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 c135f6e37a00..bb2bb3ab497a 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -366,6 +366,7 @@ 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);

I'm not up to speed with the current structure of the DMA implementation
on ARM, but isn't this going to make cache lines dirty for the returned
buffer, which will corrupt DMA on non-coherent devices?

-- 
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