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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Feb 08, 2022 at 04:23:27PM -0800, Rajat Jain wrote:
> Hello Folks,
> 
> 
> On Tue, Feb 1, 2022 at 6:01 PM Rajat Jain <rajatja@google.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.
> 
> Just to unite the threads (from
> https://www.spinics.net/lists/linux-pci/msg120221.html). I did reach
> out to Microsoft but they haven't acknowledged my email. I also pinged
> them again yesterday, but I suspect I may not be able to break the
> ice. So this patch may be ready to go in my opinion.
> 
> I don't see any outstanding comments on this patch, but please let me
> know if you have any comments.
> 
> Thanks & Best Regards,
> 
> Rajat
> 
> 
> >
> > Signed-off-by: Rajat Jain <rajatja@google.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)

Please no, "Untrusted" does not really convey much, if anything here.
You are taking an odd in-kernel-value and making it a user api.

Where is this "trust" defined?  Who defines it?  What policy does the
kernel impose on it?

By putting this value in a firmware requirement like this, it better be
documented VERY VERY well.

thanks,

greg k-h