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

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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,
        linux-tegra@...r.kernel.org,
        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.