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

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Message-ID: <34a0b098-d9c5-4605-8ce7-abd6fa59d38b@arm.com>
Date: Tue, 25 Feb 2025 14:04:29 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Robin Murphy <robin.murphy@....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 25/02/2025 11:25, Robin Murphy wrote:
> 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.

Yep, that AMD systems aren't using DMA ranges.


> 
>> Anyways, let us fix it, before cleanup
>> the infrastructure for supporting other architectures.
> 
> Reviewed-by: Robin Murphy <robin.murphy@....com>

Thanks

Suzuki

> 
>> 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 */
>