linux-kernel - Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as untrusted

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Date:   Wed, 19 Jan 2022 18:25:11 -0800
From:   Dmitry Torokhov <dtor@...gle.com>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, rajatxjain@...il.com,
        jsbarnes@...gle.com
Subject: Re: [PATCH] PCI: ACPI: Allow internal devices to be marked as untrusted

Hi Rajat,

On Wed, Jan 19, 2022 at 4:04 PM 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" property).
> This however, disallows any 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).
>
> This patch introduces 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>
> ---
>  drivers/pci/pci-acpi.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index a42dbf448860..3d9e5fa49451 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1350,12 +1350,25 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
>                 dev->external_facing = 1;
>  }
>
> +static void pci_acpi_set_untrusted(struct pci_dev *dev)
> +{
> +       u8 val;
> +
> +       if (device_property_read_u8(&dev->dev, "UntrustedDevice", &val))
> +               return;
> +
> +       /* These PCI devices are not trustworthy */
> +       if (val)
> +               dev->untrusted = 1;

Should this all be replaced with:

dev->untrusted = device_property_read_bool(&dev->dev, "UntrustedDevice");

?

Also, is this ACPI-specific? Why won't we need this for DT systems (or
do we already have this)?.

Thanks,
Dmitry