linux-kernel - Re: [PATCH v3 0/6] Add support for privileged mappings

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Date:	Fri, 22 Jul 2016 17:51:07 +0100
From:	Will Deacon <will.deacon@....com>
To:	Mitchel Humpherys <mitchelh@...eaurora.org>
Cc:	iommu@...ts.linux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jordan Crouse <jcrouse@...eaurora.org>,
	Jeremy Gebben <jgebben@...eaurora.org>,
	Patrick Daly <pdaly@...eaurora.org>,
	Pratik Patel <pratikp@...eaurora.org>,
	Thomas Zeng <tzeng@...eaurora.org>
Subject: Re: [PATCH v3 0/6] Add support for privileged mappings

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@....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@....com>

It looks pretty fiddly to merge, however. How are you planning to get
this upstream?

Will