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Message-ID: <f8b541c2-9271-fc48-dde6-166a2ed6679f@arm.com>
Date: Wed, 8 Apr 2020 16:07:33 +0100
From: Robin Murphy <robin.murphy@....com>
To: Joerg Roedel <joro@...tes.org>
Cc: Will Deacon <will@...nel.org>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Kukjin Kim <kgene@...nel.org>,
Krzysztof Kozlowski <krzk@...nel.org>,
David Woodhouse <dwmw2@...radead.org>,
Lu Baolu <baolu.lu@...ux.intel.com>,
Andy Gross <agross@...nel.org>,
Bjorn Andersson <bjorn.andersson@...aro.org>,
Matthias Brugger <matthias.bgg@...il.com>,
Rob Clark <robdclark@...il.com>,
Heiko Stuebner <heiko@...ech.de>,
Gerald Schaefer <gerald.schaefer@...ibm.com>,
Thierry Reding <thierry.reding@...il.com>,
Jonathan Hunter <jonathanh@...dia.com>,
Jean-Philippe Brucker <jean-philippe@...aro.org>,
iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
linux-samsung-soc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
linux-mediatek@...ts.infradead.org,
linux-rockchip@...ts.infradead.org, linux-s390@...r.kernel.org,
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virtualization@...ts.linux-foundation.org,
Joerg Roedel <jroedel@...e.de>
Subject: Re: [RFC PATCH 17/34] iommu/arm-smmu: Store device instead of group
in arm_smmu_s2cr
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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