Messages in this thread | | | Date | Mon, 7 Mar 2022 13:03:28 +0000 | Subject | Re: [BUG] crypto: ccree: driver does not handle case where cryptlen = authsize =0 | From | Robin Murphy <> |
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On 2022-03-07 12:47, Gilad Ben-Yossef wrote: > On Mon, Mar 7, 2022 at 2:36 PM Robin Murphy <robin.murphy@arm.com> wrote: >> >> 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. > > I understand what you are saying about why checking for conflicting > directions may be a good thing, but given that the code is as it is > right now, how are we seeing the warning for two mapping that one of > them is DMA_TO_DEVICE?
Because it's the second one that isn't. The warning is triggered by adding the DMA_FROM_DEVICE entry, which *is* checked, and finds the DMA_TO_DEVICE entry already present. What's not great is that if those two mappings happened to be made in the opposite order then it would be missed entirely.
Robin.
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