Re: [PATCH v5 06/10] swiotlb: Zero out bounce buffer for untrusted device

[Lu Baolu]

Hi,

On 7/25/19 7:49 PM, Christoph Hellwig wrote:
> > index 43c88626a1f3..edc84a00b9f9 100644
> > --- a/kernel/dma/swiotlb.c
> > +++ b/kernel/dma/swiotlb.c
> > @@ -35,6 +35,7 @@
> >   #include <linux/scatterlist.h>
> >   #include <linux/mem_encrypt.h>
> >   #include <linux/set_memory.h>
> > +#include <linux/pci.h>
> >   #ifdef CONFIG_DEBUG_FS
> >   #include <linux/debugfs.h>
> >   #endif
> > @@ -562,6 +563,11 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
> >   	 */
> >   	for (i = 0; i < nslots; i++)
> >   		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
> > +
> > +	/* Zero out the bounce buffer if the consumer is untrusted. */
> > +	if (dev_is_untrusted(hwdev))
> > +		memset(phys_to_virt(tlb_addr), 0, alloc_size);
>
> Hmm.  Maybe we need to move the untrusted flag to struct device?
> Directly poking into the pci_dev from swiotlb is a bit of a layering
> violation.

Yes. We can consider this. But I tend to think that it's worth of a
separated series. That's a reason why I defined dev_is_untrusted(). This
helper keeps the caller same when moving the untrusted flag.

> > +
> >   	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
> >   	    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
> >   		swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
>
> Also for the case where we bounce here we only need to zero the padding
> (if there is any), so I think we could optimize this a bit.

Yes. There's duplication here.

Best regards,
Baolu