linux-kernel - Re: [PATCH v2 1/2] PCI: Allow internal devices to be marked as untrusted

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Date:   Wed, 9 Feb 2022 14:03:34 -0800
From:   Rajat Jain <rajatja@...gle.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Len Brown <lenb@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajat Jain <rajatxjain@...il.com>,
        Dmitry Torokhov <dtor@...gle.com>,
        Jesse Barnes <jsbarnes@...gle.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Pavel Machek <pavel@...x.de>,
        "Oliver O'Halloran" <oohall@...il.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 1/2] PCI: Allow internal devices to be marked as untrusted

Hello,

On Wed, Feb 9, 2022 at 11:11 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Feb 2, 2022 at 3:01 AM Rajat Jain <rajatja@...gle.com> wrote:
> >
> > Today the pci_dev->untrusted is set for any devices sitting downstream
> > an external facing port (determined via "ExternalFacingPort" or the
> > "external-facing" properties).
> >
> > However, currently there is no way for internal devices to be marked as
> > untrusted.
> >
> > There are use-cases though, where a platform would like to treat an
> > internal device as untrusted (perhaps because it runs untrusted firmware
> > or offers an attack surface by handling untrusted network data etc).
> >
> > Introduce a new "UntrustedDevice" property that can be used by the
> > firmware to mark any device as untrusted.
> >
> > Signed-off-by: Rajat Jain <rajatja@...gle.com>
> > ---
> > v2: * Also use the same property for device tree based systems.
> >     * Add documentation (next patch)
> >
> >  drivers/pci/of.c       | 2 ++
> >  drivers/pci/pci-acpi.c | 1 +
> >  drivers/pci/pci.c      | 9 +++++++++
> >  drivers/pci/pci.h      | 2 ++
> >  4 files changed, 14 insertions(+)
> >
> > diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> > index cb2e8351c2cc..e8b804664b69 100644
> > --- a/drivers/pci/of.c
> > +++ b/drivers/pci/of.c
> > @@ -24,6 +24,8 @@ void pci_set_of_node(struct pci_dev *dev)
> >                                                     dev->devfn);
> >         if (dev->dev.of_node)
> >                 dev->dev.fwnode = &dev->dev.of_node->fwnode;
> > +
> > +       pci_set_untrusted(dev);
> >  }
> >
> >  void pci_release_of_node(struct pci_dev *dev)
> > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> > index a42dbf448860..2bffbd5c6114 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -1356,6 +1356,7 @@ void pci_acpi_setup(struct device *dev, struct acpi_device *adev)
> >
> >         pci_acpi_optimize_delay(pci_dev, adev->handle);
> >         pci_acpi_set_external_facing(pci_dev);
> > +       pci_set_untrusted(pci_dev);
> >         pci_acpi_add_edr_notifier(pci_dev);
> >
> >         pci_acpi_add_pm_notifier(adev, pci_dev);
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 9ecce435fb3f..41e887c27004 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -6869,3 +6869,12 @@ static int __init pci_realloc_setup_params(void)
> >         return 0;
> >  }
> >  pure_initcall(pci_realloc_setup_params);
> > +
> > +void pci_set_untrusted(struct pci_dev *pdev)
> > +{
> > +       u8 val;
> > +
> > +       if (!device_property_read_u8(&pdev->dev, "UntrustedDevice", &val)
> > +           && val)
> > +               pdev->untrusted = 1;
>
> I'm not sure why you ignore val = 0.  Is it not a valid value?

I'm following the other similar properties that Bjorn mentioned. The
pdev->untrusted is already initialized to 0 so it wouldn't matter.

>
> The property is not particularly well defined here.  It is not clear
> from its name that it only applies to PCI devices and how.
>
> AFAICS, the "untrusted" bit affected by it is only used by the ATS
> code and in one PCH ACS quirk, but I'm not sure if this is all you
> have in mind.

I hope my other response addressed this one.

Thanks & Best Regards,

Rajat

>
> > +}
> > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > index 3d60cabde1a1..6c273ce5e0ba 100644
> > --- a/drivers/pci/pci.h
> > +++ b/drivers/pci/pci.h
> > @@ -761,4 +761,6 @@ static inline pci_power_t mid_pci_get_power_state(struct pci_dev *pdev)
> >  }
> >  #endif
> >
> > +void pci_set_untrusted(struct pci_dev *pdev);
> > +
> >  #endif /* DRIVERS_PCI_H */
> > --
> > 2.35.0.rc2.247.g8bbb082509-goog
> >