Messages in this thread | | | From | Mitchel Humpherys <> | Subject | Re: [PATCH v3 0/6] Add support for privileged mappings | Date | Mon, 25 Jul 2016 12:01:05 -0700 |
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On Mon, Jul 25 2016 at 10:50:13 AM, Will Deacon <will.deacon@arm.com> wrote: > On Fri, Jul 22, 2016 at 01:39:45PM -0700, Mitchel Humpherys wrote: >> 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? > > Fiddly in that it touches multiple subsystems. I guess routing it via > the iommu tree (Joerg) might be the best bet.
Sounds good. I'm going to rebase on linux-next as well anyways to get the new dma attrs format and resend.
-Mitch
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