Re: [PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"

[Rafael J. Wysocki]

On Fri, Mar 25, 2022 at 7:46 PM Rajat Jain <rajatja@xxxxxxxxxx> wrote:
>
> The "DmaProperty" is supported and documented by Microsoft here:
> https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
> They use this property for DMA protection:
> https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
>
> Support the "DmaProperty" with the same semantics. This is useful for
> internal PCI devices that do not hang off a PCIe rootport, but offer
> an attack surface for DMA attacks (e.g. internal network devices).
>
> Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx>
> Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

> ---
> v5: * Reorder the patches in the series
> v4: * Add the GUID.
>     * Update the comment and commitlog.
> v3: * Use Microsoft's documented property "DmaProperty"
>     * Resctrict to ACPI only
>
>  drivers/acpi/property.c |  3 +++
>  drivers/pci/pci-acpi.c  | 16 ++++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> index d0986bda2964..20603cacc28d 100644
> --- a/drivers/acpi/property.c
> +++ b/drivers/acpi/property.c
> @@ -48,6 +48,9 @@ static const guid_t prp_guids[] = {
>         /* Storage device needs D3 GUID: 5025030f-842f-4ab4-a561-99a5189762d0 */
>         GUID_INIT(0x5025030f, 0x842f, 0x4ab4,
>                   0xa5, 0x61, 0x99, 0xa5, 0x18, 0x97, 0x62, 0xd0),
> +       /* DmaProperty for PCI devices GUID: 70d24161-6dd5-4c9e-8070-705531292865 */
> +       GUID_INIT(0x70d24161, 0x6dd5, 0x4c9e,
> +                 0x80, 0x70, 0x70, 0x55, 0x31, 0x29, 0x28, 0x65),
>  };
>
>  /* ACPI _DSD data subnodes GUID: dbb8e3e6-5886-4ba6-8795-1319f52a966b */
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 1f15ab7eabf8..378e05096c52 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1350,12 +1350,28 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
>                 dev->external_facing = 1;
>  }
>
> +static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
> +{
> +       u8 val;
> +
> +       /*
> +        * Property also used by Microsoft Windows for same purpose,
> +        * (to implement DMA protection from a device, using the IOMMU).
> +        */
> +       if (device_property_read_u8(&dev->dev, "DmaProperty", &val))
> +               return;
> +
> +       if (val)
> +               dev->untrusted = 1;
> +}
> +
>  void pci_acpi_setup(struct device *dev, struct acpi_device *adev)
>  {
>         struct pci_dev *pci_dev = to_pci_dev(dev);
>
>         pci_acpi_optimize_delay(pci_dev, adev->handle);
>         pci_acpi_set_external_facing(pci_dev);
> +       pci_acpi_check_for_dma_protection(pci_dev);
>         pci_acpi_add_edr_notifier(pci_dev);
>
>         pci_acpi_add_pm_notifier(adev, pci_dev);
> --
> 2.35.1.1021.g381101b075-goog
>