linux-kernel - Re: [PATCH] iommu/vt-d: Don't apply gfx quirks to untrusted devices

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Message-ID: <CACK8Z6F2n6yx7Fs43rmUQko3PAHZYcnc_eyE_xPdUHXwf2hhLw@mail.gmail.com>
Date:   Tue, 2 Jun 2020 18:43:00 +0000
From:   Rajat Jain <rajatja@...gle.com>
To:     Mika Westerberg <mika.westerberg@...el.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        "Krishnakumar, Lalithambika" <lalithambika.krishnakumar@...el.com>,
        Rajat Jain <rajatxjain@...il.com>,
        Prashant Malani <pmalani@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Alex Levin <levinale@...gle.com>,
        Zubin Mithra <zsm@...gle.com>,
        Mattias Nissler <mnissler@...gle.com>,
        Todd Broch <tbroch@...gle.com>
Subject: Re: [PATCH] iommu/vt-d: Don't apply gfx quirks to untrusted devices

Hi MIka,

Thanks for taking a look.

On Tue, Jun 2, 2020 at 2:50 AM Mika Westerberg
<mika.westerberg@...el.com> wrote:
>
> On Mon, Jun 01, 2020 at 10:45:17PM -0700, Rajat Jain wrote:
> > Currently, an external malicious PCI device can masquerade the VID:PID
> > of faulty gfx devices, and thus apply iommu quirks to effectively
> > disable the IOMMU restrictions for itself.
> >
> > Thus we need to ensure that the device we are applying quirks to, is
> > indeed an internal trusted device.
> >
> > Signed-off-by: Rajat Jain <rajatja@...gle.com>
> > ---
> >  drivers/iommu/intel-iommu.c | 28 ++++++++++++++++++++++++++++
> >  1 file changed, 28 insertions(+)
> >
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index ef0a5246700e5..f2a480168a02f 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -6214,6 +6214,11 @@ const struct iommu_ops intel_iommu_ops = {
> >
> >  static void quirk_iommu_igfx(struct pci_dev *dev)
> >  {
> > +     if (dev->untrusted) {
> > +             pci_warn(dev, "skipping iommu quirk for untrusted gfx dev\n");
>
> I think you should be consistent with other messages. For example iommu
> should be spelled IOMMU as done below.
>
> Also this is visible to users so maybe put bit more information there:
>
>   pci_warn(dev, "Will not apply IOMMU quirk for untrusted graphics device\n");
>
> Ditto for all the other places. Also is "untrusted" good word here? If
> an ordinary user sees this will it trigger some sort of panic reaction.
> Perhaps we should call it "potentially untrusted" or something like
> that?

Fixed it, posted new patch at
https://lkml.org/lkml/2020/6/2/822

Thanks,

Rajat

>
> > +             return;
> > +     }
> > +
> >       pci_info(dev, "Disabling IOMMU for graphics on this chipset\n");
> >       dmar_map_gfx = 0;