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SubjectRe: [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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