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

[Robin Murphy]

On 2022-03-07 12:47, Gilad Ben-Yossef wrote:
> On Mon, Mar 7, 2022 at 2:36 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> > On 2022-03-07 12:17, Gilad Ben-Yossef wrote:
> > > On Mon, Mar 7, 2022 at 1:14 PM Robin Murphy <robin.murphy@xxxxxxx> 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.