linux-kernel - Re: [PATCH v5 5/9] iommu/arm-smmu-v3: Refactor write_ctx

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Message-ID: <ZNtgD3LKwS4eatoe@nvidia.com>
Date:   Tue, 15 Aug 2023 08:22:55 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     Will Deacon <will@...nel.org>, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        robin.murphy@....com, nicolinc@...dia.com, jean-philippe@...aro.org
Subject: Re: [PATCH v5 5/9] iommu/arm-smmu-v3: Refactor write_ctx_desc

On Tue, Aug 15, 2023 at 01:20:04PM +0800, Michael Shavit wrote:
> On Thu, Aug 10, 2023 at 11:39 PM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > Actually, I don't think this even works as nothing on the PASID path
> > adds to the list that arm_smmu_write_ctx_desc_devices() iterates over ??
> >
> > Then the remaining two calls:
> >
> > arm_smmu_share_asid(struct mm_struct *mm, u16 asid)
> >         arm_smmu_write_ctx_desc_devices(smmu_domain, 0, cd);
> >
> >         This is OK only if the sketchy assumption that the CD
> >         we extracted for a conflicting ASID is not asigned to a PASID.
> >
> > static void arm_smmu_mm_release(struct mmu_notifier *mn, struct mm_struct *mm)
> >         arm_smmu_write_ctx_desc_devices(smmu_domain, mm->pasid, &quiet_cd);
> >
> >         This doesn't work because we didn't add the master to the list
> >         during __arm_smmu_sva_bind and this path is expressly working
> >         on the PASID binds, not the RID binds.
> 
> Actually it is working on the RID attached domain (as returned by
> iommu_get_domain_for_dev() at sva_bind time) not the SVA domain
> here...

That can't be right, the purpose of that call and arm_smmu_mm_release is to
disable the PASID that is about the UAF the mm's page table.

Jason