Re: [RFC PATCH 17/34] iommu/arm-smmu: Store device instead of group in arm_smmu_s2cr

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On 2020-04-08 3:37 pm, Joerg Roedel wrote:
Hi Robin,

thanks for looking into this.

On Wed, Apr 08, 2020 at 01:09:40PM +0100, Robin Murphy wrote:
For a hot-pluggable bus where logical devices may share Stream IDs (like
fsl-mc), this could happen:

   create device A
   iommu_probe_device(A)
     iommu_device_group(A) -> alloc group X
   create device B
   iommu_probe_device(B)
     iommu_device_group(A) -> lookup returns group X
   ...
   iommu_remove_device(A)
   delete device A
   create device C
   iommu_probe_device(C)
     iommu_device_group(C) -> use-after-free of A

Preserving the logical behaviour here would probably look *something* like
the mangled diff below, but I haven't thought it through 100%.

Yeah, I think you are right. How about just moving the loop which sets
s2crs[idx].group to arm_smmu_device_group()? In that case I can drop
this patch and leave the group pointer in place.

Isn't that exactly what I suggested? :)

I don't recall for sure, but knowing me, that bit of group bookkeeping is only where it currently is because it cheekily saves iterating the IDs a second time. I don't think there's any technical reason.

Robin.



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