From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v3 0/6] Add support for privileged mappings Date: Mon, 25 Jul 2016 10:50:13 +0100 Message-ID: <20160725095012.GC15864@arm.com> References: <20160719203655.16629-1-mitchelh@codeaurora.org> <20160722165107.GH16837@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Mitchel Humpherys Cc: iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Robin Murphy , Marek Szyprowski , Jordan Crouse , Jeremy Gebben , Patrick Daly , Pratik Patel , Thomas Zeng List-Id: iommu@lists.linux-foundation.org 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 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 > >> 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 > > > > 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. Will