[PATCH v3 0/6] Add support for privileged mappings

On Mon, Jul 25 2016 at 10:50:13 AM, Will Deacon [off-list ref] wrote:

On Fri, Jul 22, 2016 at 01:39:45PM -0700, Mitchel Humpherys wrote:

quoted

On Fri, Jul 22 2016 at 05:51:07 PM, Will Deacon [off-list ref] wrote:

quoted

On Tue, Jul 19, 2016 at 01:36:49PM -0700, Mitchel Humpherys wrote:

quoted

The following patch to the ARM SMMU driver:

    commit d346180e70b91b3d5a1ae7e5603e65593d4622bc
    Author: Robin Murphy [off-list ref]
    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 <redacted>

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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