Subject: [PATCHv3 1/2] arm64: Check for NULL device before getting the coherent_dma_mask

From: [email-masked] (Laura Abbott)
Date: Wed, 11 Dec 2013 09:48:10 -0800

On 12/11/2013 2:42 AM, Will Deacon wrote:
> On Tue, Dec 10, 2013 at 09:43:35PM +0000, Laura Abbott wrote:
>> The device passed in to dma_alloc may be NULL. Check for this before
>> trying to get the coherent_dma_mask.
>>
>> Cc: Will Deacon <[email-masked]>
>> Cc: Catalin Marinas <[email-masked]>
>> Cc: Marek Szyprowski <[email-masked]>
>> Signed-off-by: Laura Abbott <[email-masked]>
>> ---
>>   arch/arm64/mm/dma-mapping.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>> index 4bd7579..4134212 100644
>> --- a/arch/arm64/mm/dma-mapping.c
>> +++ b/arch/arm64/mm/dma-mapping.c
>> @@ -33,7 +33,7 @@ static void *arm64_swiotlb_alloc_coherent(struct device *dev, size_t size,
>>   					  dma_addr_t *dma_handle, gfp_t flags,
>>   					  struct dma_attrs *attrs)
>>   {
>> -	if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
>> +	if (dev && IS_ENABLED(CONFIG_ZONE_DMA32) &&
>>   	    dev->coherent_dma_mask <= DMA_BIT_MASK(32))
>>   		flags |= GFP_DMA32;
>>   	return swiotlb_alloc_coherent(dev, size, dma_handle, flags);
>
> Unless I'm misreading the code, it looks like there are paths through
> swiotlb_alloc_coherent that will dereference the dev parameter without a
> NULL check. Are you sure we should allow for NULL devices here?
>

The current ARM code allows for NULL devices so that would be a 
difference in behavior between arm and arm64. We're also relying on this 
behavior in some code. Where exactly in swiotlb_alloc_coherent does this 
dereference happen? The only one I see is checked with 'if (hwdev && 
hwdev->coherent_dma_mask)'

> Will

Thanks,
Laura
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