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Date:   Sat, 19 Mar 2022 23:29:06 -0700
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Subject: [PATCH v4 2/2] PCI: ACPI: Support Microsoft's "DmaProperty"
From:   Rajat Jain <rajatja@google.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>, linux-pci@vger.kernel.org,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rajat Jain <rajatxjain@gmail.com>,
        Dmitry Torokhov <dtor@google.com>,
        Jesse Barnes <jsbarnes@google.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Pavel Machek <pavel@denx.de>,
        "Oliver O'Halloran" <oohall@gmail.com>,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        iommu@lists.linux-foundation.org
Cc:     Rajat Jain <rajatja@google.com>
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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>
---
v4: * Add the GUID. 
    * Use the (now) renamed property - pci_dev->poses_dma_risk)
    * 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..5360f1af2ed3 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->poses_dma_risk = 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);
-- 
2.35.1.894.gb6a874cedc-goog