linux-kernel - Re: [PATCH v2 1/3] dma: Fix encryption bit clearing for dma_to

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Message-ID: <68405608-564c-4e79-9cbc-545626e736f1@arm.com>
Date: Tue, 25 Feb 2025 11:25:38 +0000
From: Robin Murphy <robin.murphy@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>, will@...nel.org,
 catalin.marinas@....com
Cc: maz@...nel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
 aneesh.kumar@...nel.org, steven.price@....com,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Christoph Hellwig <hch@....de>, Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v2 1/3] dma: Fix encryption bit clearing for dma_to_phys

On 2025-02-19 10:07 pm, Suzuki K Poulose wrote:
> phys_to_dma() sets the encryption bit on the translated DMA address. But
> dma_to_phys() clears the encryption bit after it has been translated back
> to the physical address, which could fail if the device uses DMA ranges.
> 
> Hopefully, AMD SME doesn't use it.

...by which you mean we don't think any AMD systems are using the ACPI 
_DMA method to constrain physical DMA ranges, otherwise SME with 
dma-direct would presumably already be broken by this lookup going wrong.

> Anyways, let us fix it, before cleanup
> the infrastructure for supporting other architectures.

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Reported-by: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
> Link: https://lkml.kernel.org/r/yq5amsen9stc.fsf@kernel.org
> Cc: Will Deacon <will@...nel.org>
> Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Steven Price <steven.price@....com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>   include/linux/dma-direct.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index d7e30d4f7503..d20ecc24cb0f 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -101,12 +101,13 @@ static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t dma_addr)
>   {
>   	phys_addr_t paddr;
>   
> +	dma_addr = __sme_clr(dma_addr);
>   	if (dev->dma_range_map)
>   		paddr = translate_dma_to_phys(dev, dma_addr);
>   	else
>   		paddr = dma_addr;
>   
> -	return __sme_clr(paddr);
> +	return paddr;
>   }
>   #endif /* !CONFIG_ARCH_HAS_PHYS_TO_DMA */
>