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    SubjectRe: [PATCH v3 0/6] Add support for privileged mappings
    Date
    On Fri, Jul 22 2016 at 05:51:07 PM, Will Deacon <will.deacon@arm.com> wrote:
    > On Tue, Jul 19, 2016 at 01:36:49PM -0700, Mitchel Humpherys wrote:
    >> The following patch to the ARM SMMU driver:
    >>
    >> commit d346180e70b91b3d5a1ae7e5603e65593d4622bc
    >> Author: Robin Murphy <robin.murphy@arm.com>
    >> Date: Tue Jan 26 18:06:34 2016 +0000
    >>
    >> iommu/arm-smmu: Treat all device transactions as unprivileged
    >>
    >> started forcing all SMMU transactions to come through as "unprivileged".
    >> The rationale given was that:
    >>
    >> (1) There is no way in the IOMMU API to even request privileged mappings.
    >>
    >> (2) It's difficult to implement a DMA mapper that correctly models the
    >> ARM VMSAv8 behavior of unprivileged-writeable =>
    >> privileged-execute-never.
    >>
    >> This series rectifies (1) by introducing an IOMMU API for privileged
    >> mappings and implements it in io-pgtable-arm.
    >>
    >> This series rectifies (2) by introducing a new dma attribute
    >> (DMA_ATTR_PRIVILEGED) for users of the DMA API that need privileged
    >> mappings which are inaccessible to lesser-privileged execution levels, and
    >> implements it in the arm64 IOMMU DMA mapper. The one known user (pl330.c)
    >> is converted over to the new attribute.
    >>
    >> Jordan and Jeremy can provide more info on the use case if needed, but the
    >> high level is that it's a security feature to prevent attacks such as [1].
    >
    > This all looks good to me:
    >
    > Acked-by: Will Deacon <will.deacon@arm.com>
    >
    > It looks pretty fiddly to merge, however. How are you planning to get
    > this upstream?

    Fiddly in what way? Do you mean in relation to "dma-mapping: Use
    unsigned long for dma_attrs" [1]? I admit I wasn't aware of that
    activity until Robin mentioned it. It looks like it's merged on
    next/master, shall I rebase/rework on that and resend?

    [1] https://lkml.org/lkml/2016/7/13/198


    -Mitch

    --
    Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
    a Linux Foundation Collaborative Project

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