[PATCH v7 1/2] PCI/ACPI: Support Microsoft's "DmaProperty"

* [PATCH v7 1/2] PCI/ACPI: Support Microsoft's "DmaProperty"
@ 2022-04-26 17:21 Rajat Jain
  2022-04-26 17:21 ` [PATCH v7 2/2] PCI: Rename pci_dev->untrusted to pci_dev->untrusted_dma Rajat Jain
  0 siblings, 1 reply; 2+ messages in thread
From: Rajat Jain @ 2022-04-26 17:21 UTC (permalink / raw)
  To: Rafael J. Wysocki, Len Brown, linux-pci, Mika Westerberg,
	Greg Kroah-Hartman, Bjorn Helgaas, Bjorn Helgaas,
	ACPI Devel Maling List, Linux Kernel Mailing List, Rajat Jain,
	Dmitry Torokhov, Jesse Barnes, Jean-Philippe Brucker,
	Pavel Machek, Oliver O'Halloran, Joerg Roedel, Will Deacon,
	David Woodhouse, Lu Baolu, iommu
  Cc: Rajat Jain, Rafael J . Wysocki

The "DmaProperty" is supported and currently documented and used by
Microsoft [link 1 below], to flag internal PCIe root ports that need
DMA protection [link 2 below]. We have discussed with them and reached
a common understanding that they shall change their MSDN documentation
to say that the same property can be used to protect any PCI device,
and not just internal PCIe root ports (since there is no point
introducing yet another property for arbitrary PCI devices). This helps
with security from internal devices that offer an attack surface for
DMA attacks (e.g. internal network devices).

Support DmaProperty to mark DMA from a PCI device as untrusted.

Link: [1] https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-internal-pcie-ports-accessible-to-users-and-requiring-dma-protection
Link: [2] https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
Signed-off-by: Rajat Jain <rajatja@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
v7: * Update the comment, based on feedback.
v6: * Take care of Bjorn's comments:
       - Update the commit log
       - Rename to pci_dev_has_dma_property()
       - Use acpi_dev_get_property()
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  | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
index 12bbfe833609..bafe35c301ac 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 3ae435beaf0a..8cb4725d41fa 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1369,12 +1369,34 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
 		dev->external_facing = 1;
 }
 
+static int pci_dev_has_dma_property(struct pci_dev *dev)
+{
+	struct acpi_device *adev;
+	const union acpi_object *obj;
+
+	adev = ACPI_COMPANION(&dev->dev);
+	if (!adev)
+		return 0;
+
+	/*
+	 * Property used by Microsoft Windows to enforce IOMMU DMA
+	 * protection from any device, that the system may not fully trust;
+	 * we'll honour it the same way.
+	 */
+	if (!acpi_dev_get_property(adev, "DmaProperty", ACPI_TYPE_INTEGER,
+				   &obj) && obj->integer.value == 1)
+		return 1;
+
+	return 0;
+}
+
 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_dev->untrusted |= pci_dev_has_dma_property(pci_dev);
 	pci_acpi_add_edr_notifier(pci_dev);
 
 	pci_acpi_add_pm_notifier(adev, pci_dev);
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog


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