PCI: pciehp: Detect device replacement during system sleep

Ricky reports that replacing a device in a hotplug slot during ACPI sleep
state S3 does not cause re-enumeration on resume, as one would expect.
Instead, the new device is treated as if it was the old one.

There is no bulletproof way to detect device replacement, but as a
heuristic, check whether the device identity in config space matches cached
data in struct pci_dev (Vendor ID, Device ID, Class Code, Revision ID,
Subsystem Vendor ID, Subsystem ID). Additionally, cache and compare the
Device Serial Number (PCIe r6.2 sec 7.9.3). If a mismatch is detected,
mark the old device disconnected (to prevent its driver from accessing the
new device) and synthesize a Presence Detect Changed event.

The device identity in config space which is compared here is the same as
the one included in the signed Subject Alternative Name per PCIe r6.1 sec
6.31.3. Thus, the present commit prevents attacks where a valid device is
replaced with a malicious device during system sleep and the valid device's
driver obliviously accesses the malicious device.

This is about as much as can be done at the PCI layer. Drivers may have
additional ways to identify devices (such as reading a WWID from some
register) and may trigger re-enumeration when detecting an identity change
on resume.

Link: https://lore.kernel.org/r/[e-mail]
Reported-by: Ricky Wu <[e-mail]>
Closes: https://lore.kernel.org/r/[e-mail]
Tested-by: Ricky Wu <[e-mail]>
Signed-off-by: Lukas Wunner <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>

drivers/pci/hotplug/pciehp.h

···
 /**
  * struct controller - PCIe hotplug controller
  * @pcie: pointer to the controller's PCIe port service device
+ * @dsn: cached copy of Device Serial Number of Function 0 in the hotplug slot
+ *	(PCIe r6.2 sec 7.9.3); used to determine whether a hotplugged device
+ *	was replaced with a different one during system sleep
  * @slot_cap: cached copy of the Slot Capabilities register
  * @inband_presence_disabled: In-Band Presence Detect Disable supported by
  *	controller and disabled per spec recommendation (PCIe r5.0, appendix I
···
  */
 struct controller {
 	struct pcie_device *pcie;
+	u64 dsn;
 
 	u32 slot_cap;				/* capabilities and quirks */
 	unsigned int inband_presence_disabled:1;

drivers/pci/hotplug/pciehp_core.c

···
 	return 0;
 }
 
+static bool pciehp_device_replaced(struct controller *ctrl)
+{
+	struct pci_dev *pdev __free(pci_dev_put);
+	u32 reg;
+
+	pdev = pci_get_slot(ctrl->pcie->port->subordinate, PCI_DEVFN(0, 0));
+	if (!pdev)
+		return true;
+
+	if (pci_read_config_dword(pdev, PCI_VENDOR_ID, &reg) ||
+	    reg != (pdev->vendor | (pdev->device << 16)) ||
+	    pci_read_config_dword(pdev, PCI_CLASS_REVISION, &reg) ||
+	    reg != (pdev->revision | (pdev->class << 8)))
+		return true;
+
+	if (pdev->hdr_type == PCI_HEADER_TYPE_NORMAL &&
+	    (pci_read_config_dword(pdev, PCI_SUBSYSTEM_VENDOR_ID, &reg) ||
+	     reg != (pdev->subsystem_vendor | (pdev->subsystem_device << 16))))
+		return true;
+
+	if (pci_get_dsn(pdev) != ctrl->dsn)
+		return true;
+
+	return false;
+}
+
 static int pciehp_resume_noirq(struct pcie_device *dev)
 {
 	struct controller *ctrl = get_service_data(dev);
···
 	ctrl->cmd_busy = true;
 
 	/* clear spurious events from rediscovery of inserted card */
-	if (ctrl->state == ON_STATE || ctrl->state == BLINKINGOFF_STATE)
+	if (ctrl->state == ON_STATE || ctrl->state == BLINKINGOFF_STATE) {
 		pcie_clear_hotplug_events(ctrl);
+
+		/*
+		 * If hotplugged device was replaced with a different one
+		 * during system sleep, mark the old device disconnected
+		 * (to prevent its driver from accessing the new device)
+		 * and synthesize a Presence Detect Changed event.
+		 */
+		if (pciehp_device_replaced(ctrl)) {
+			ctrl_dbg(ctrl, "device replaced during system sleep\n");
+			pci_walk_bus(ctrl->pcie->port->subordinate,
+				     pci_dev_set_disconnected, NULL);
+			pciehp_request(ctrl, PCI_EXP_SLTSTA_PDC);
+		}
+	}
 
 	return 0;
 }

drivers/pci/hotplug/pciehp_hpc.c

···
 		}
 	}
 
+	pdev = pci_get_slot(subordinate, PCI_DEVFN(0, 0));
+	if (pdev)
+		ctrl->dsn = pci_get_dsn(pdev);
+	pci_dev_put(pdev);
+
 	return ctrl;
 }
 

drivers/pci/hotplug/pciehp_pci.c

···
 	pci_bus_add_devices(parent);
 	down_read_nested(&ctrl->reset_lock, ctrl->depth);
 
+	dev = pci_get_slot(parent, PCI_DEVFN(0, 0));
+	ctrl->dsn = pci_get_dsn(dev);
+	pci_dev_put(dev);
+
  out:
 	pci_unlock_rescan_remove();
 	return ret;