Re: [BUG] crypto: ccree: driver does not handle case where cryptlen = authsize =0

[Robin Murphy <robin.murphy@arm.com>]

On 2022-03-07 12:17, Gilad Ben-Yossef wrote:
> On Mon, Mar 7, 2022 at 1:14 PM Robin Murphy <robin.murphy@arm.com> wrote:
> 
>> The "overlap" is in the sense of having more than one mapping within the
>> same cacheline:
>>
>> [  142.458120] DMA-API: add_dma_entry start P=ba79f200 N=ba79f
>> D=ba79f200 L=10 DMA_FROM_DEVICE attrs=0
>> [  142.458156] DMA-API: add_dma_entry start P=445dc010 N=445dc
>> D=445dc010 L=10 DMA_TO_DEVICE attrs=0
>> [  142.458178] sun8i-ss 1c15000.crypto: SRC 0/1/1 445dc000 len=16 bi=0
>> [  142.458215] sun8i-ss 1c15000.crypto: DST 0/1/1 ba79f200 len=16 bi=0
>> [  142.458234] DMA-API: add_dma_entry start P=ba79f210 N=ba79f
>> D=ba79f210 L=10 DMA_FROM_DEVICE attrs=0
>>
>> This actually illustrates exactly the reason why this is unsupportable.
>> ba79f200 is mapped for DMA_FROM_DEVICE, therefore subsequently mapping
>> ba79f210 for DMA_TO_DEVICE may cause the cacheline covering the range
>> ba79f200-ba79f23f to be written back over the top of data that the
>> device has already started to write to memory. Hello data corruption.
>>
>> Separate DMA mappings should be from separate memory allocations,
>> respecting ARCH_DMA_MINALIGN.
> 
> hmm... I know I'm missing something here, but how does this align with
> the following from active_cacheline_insert() in kernel/dma/debug.c ?
> 
>          /* If the device is not writing memory then we don't have any
>           * concerns about the cpu consuming stale data.  This mitigates
>           * legitimate usages of overlapping mappings.
>           */
>          if (entry->direction == DMA_TO_DEVICE)
>                  return 0;

It's OK to have multiple mappings that are *all* DMA_TO_DEVICE, which 
looks to be the case that this check was intended to allow. However I 
think you're right that it should still actually check for conflicting 
directions between the new entry and any existing ones, otherwise it 
ends up a bit too lenient.

Cheers,
Robin.