linux-kernel - Re: [PATCH] iommu: Avoid NULL group dereference

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Date:   Fri, 18 Aug 2017 11:42:09 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux-foundation.org, shawn.lin@...k-chips.com,
        marc.zyngier@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: Avoid NULL group dereference

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