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SubjectRe: [PATCH v5 0/6] Add support for privileged mappings
On Wed, Jul 27, 2016 at 04:42:02PM -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].
>
> Joerg, the v3 series was previously acked by Will [2]. He also recommended
> that we take all of this through your tree since it's touching multiple
> subsystems [3]. Can you please take a look? Thanks!

You forgot to add my ack to the patches, so if you need it again:

Acked-by: Will Deacon <will.deacon@arm.com>

Will

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