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    Subject[PATCH v5 1/2] PCI: ACPI: Support Microsoft's "DmaProperty"
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    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@google.com>
    Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    ---
    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
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