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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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