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

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Message-Id: <20220120000409.2706549-1-rajatja@google.com>
Date:   Wed, 19 Jan 2022 16:04:09 -0800
From:   Rajat Jain <rajatja@...gle.com>
To:     "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
Cc:     Rajat Jain <rajatja@...gle.com>, rajatxjain@...il.com,
        dtor@...gle.com, jsbarnes@...gle.com
Subject: [PATCH] PCI: ACPI: Allow internal devices to be marked as untrusted

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;
+}
+
 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_set_untrusted(pci_dev);
 	pci_acpi_add_edr_notifier(pci_dev);
 
 	pci_acpi_add_pm_notifier(adev, pci_dev);
-- 
2.34.1.703.g22d0c6ccf7-goog