Re: [PATCH] iommu: Avoid NULL group dereference

Joerg Roedel
2017-08-18T09:42:09Z

On Thu, Aug 17, 2017 at 05:56:23PM +0100, Robin Murphy wrote:
> On 17/08/17 16:41, Joerg Roedel wrote:
> > Okay, so just to check I got it right: Drivers do the above to check
> > whether a device is managed by an IOMMU, and that crashes now because
> > the 'group == NULL' check was removed?
>
> Indeed - the typical context is network descriptors that don't have
> space to store the CPU virtual address of the buffer, so when a packet
> arrives the driver has to work backwards from the DMA address, in this
> sort of pattern:
>
> addr = desc[idx]->addr;
> domain = iommu_get_domain_for_dev(dev);
> if (domain)
> addr = iommu_iova_to_phys(domain, addr)
> buf = phys_to_virt(addr)
>
> (the GIC thing is similar but in reverse, with a physical address which
> may or may not need replacing with an IOVA). Unless we were to change
> the interface to be iommu_get_domain_for_group(), I think it makes sense
> for it to remain valid to call for any device.

Okay, we should find a better solution for this at some point, but I
applied the patch for now.

Joerg