linux-kernel - Re: [PATCH 01/12] iommu/vt-d: Use iommu_get_domain_for

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Message-ID: <20220531155904.GA3726345@nvidia.com>
Date:   Tue, 31 May 2022 12:59:04 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        iommu@...ts.linux-foundation.org,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 01/12] iommu/vt-d: Use iommu_get_domain_for_dev() in
 debugfs

On Tue, May 31, 2022 at 02:52:28PM +0100, Robin Murphy wrote:

> > +                break;
> > +            pgtable_walk_level(m, phys_to_virt(phys_addr),
> 
> Also, obligatory reminder that pfn_valid() only means that pfn_to_page()
> gets you a valid struct page. Whether that page is direct-mapped kernel
> memory or not is a different matter.

Even though this is debugfs, if the operation is sketchy like that and
can theortically crash the kernel the driver should test capabilities,
CAP_SYS_RAWIO or something may be appropriate. I don't think we have a
better cap for 'userspace may crash the kernel'

Jason