PCI/CMA: Authenticate devices on enumeration

This currently very much a PoC.  Currently the SPDM library only provides
a single function to allow a challenge / authentication of the PCI EP.

SPDM exchanges must occur in one of a small set of valid squences over
which the message digest used in authentication is built up.
Placing that complexity in the SPDM library seems like a good way
to enforce that logic, without having to do it for each transport.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>

drivers/pci/Kconfig

@@ -116,6 +116,15 @@ config XEN_PCIDEV_FRONTEND
 config PCI_ATS
 	bool
 
+config PCI_CMA
+	bool "Component Measurement and Authentication (CMA/SPDM)"
+	select PCI_DOE
+	select SPDM
+	help
+	  Authenticate devices on enumeration per PCIe r6.0 sec 6.31.
+	  A PCI DOE mailbox is used as transport for DMTF SPDM based
+	  attestation, measurement and secure channel establishment.
+
 config PCI_DOE
 	bool
 

drivers/pci/Makefile

@@ -32,6 +32,7 @@ obj-$(CONFIG_PCI_P2PDMA)	+= p2pdma.o
 obj-$(CONFIG_XEN_PCIDEV_FRONTEND) += xen-pcifront.o
 obj-$(CONFIG_VGA_ARB)		+= vgaarb.o
 obj-$(CONFIG_PCI_DOE)		+= doe.o
+obj-$(CONFIG_PCI_CMA)		+= cma.o
 
 # Endpoint library must be initialized before its users
 obj-$(CONFIG_PCI_ENDPOINT)	+= endpoint/

drivers/pci/cma.c

@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Component Measurement and Authentication (CMA/SPDM, PCIe r6.0 sec 6.31)
+ *
+ * Copyright (C) 2021 Huawei
+ *     Jonathan Cameron <Jonathan.Cameron@huawei.com>
+ *
+ * Copyright (C) 2022 Intel Corporation
+ */
+
+#define dev_fmt(fmt) "CMA: " fmt
+
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/pci-doe.h>
+#include <linux/pm_runtime.h>
+#include <linux/spdm.h>
+
+#include "pci.h"
+
+#define PCI_DOE_PROTOCOL_CMA 1
+
+/* Keyring that userspace can poke certs into */
+static struct key *cma_keyring;
+
+static int spdm_doe_transport(void *priv, struct device *dev,
+			      void *request, size_t request_sz,
+			      void *response, size_t response_sz)
+{
+	struct pci_doe_mb *doe = priv;
+	int rc;
+
+	/*
+	 * CMA/SPDM operation in non-D0 states is optional (PCIe r6.0
+	 * sec 6.31.3).  The spec does not define a way to determine
+	 * if it's supported, so resume to D0.
+	 */
+	rc = pm_runtime_resume_and_get(dev);
+	if (rc)
+		return rc;
+
+	rc = pci_doe(doe, PCI_VENDOR_ID_PCI_SIG, PCI_DOE_PROTOCOL_CMA,
+		     request, request_sz, response, response_sz);
+
+	pm_runtime_put(dev);
+
+	return rc;
+}
+
+void pci_cma_init(struct pci_dev *pdev)
+{
+	struct spdm_state *spdm_state;
+	struct pci_doe_mb *doe;
+	int rc;
+
+	if (!pci_is_pcie(pdev))
+		return;
+
+	/* CMA/SPDM does not apply to Root Ports (PCIe r6.0 sec 6.31.3) */
+	if (pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT)
+		return;
+
+	doe = pci_find_doe_mailbox(pdev, PCI_VENDOR_ID_PCI_SIG,
+				   PCI_DOE_PROTOCOL_CMA);
+	if (!doe)
+		return;
+
+	spdm_state = spdm_create(spdm_doe_transport, doe, &pdev->dev,
+				 cma_keyring);
+	if (!spdm_state)
+		return;
+
+	rc = spdm_authenticate(spdm_state);
+	if (rc)
+		pci_info(pdev, "No CMA support\n");
+	else
+		pci_info(pdev, "Attestation passed\n");
+
+	kfree(spdm_state);
+}
+
+__init static int cma_keyring_init(void)
+{
+	cma_keyring = keyring_alloc("_cma",
+				    KUIDT_INIT(0), KGIDT_INIT(0),
+				    current_cred(),
+				    (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+				    KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE | KEY_USR_SEARCH,
+				    KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_SET_KEEP, NULL, NULL);
+	if (IS_ERR(cma_keyring))
+		pr_err("Could not allocate cma keyring\n");
+
+	return 0;
+}
+device_initcall(cma_keyring_init);
+
+MODULE_LICENSE("GPL");

drivers/pci/pci.h

@@ -787,6 +787,12 @@ static inline void pci_doe_stop(struct pci_dev *pdev) { }
 static inline void pci_doe_destroy(struct pci_dev *pdev) { }
 #endif
 
+#ifdef CONFIG_PCI_CMA
+void pci_cma_init(struct pci_dev *pdev);
+#else
+static inline void pci_cma_init(struct pci_dev *pdev) { }
+#endif
+
 /*
  * Config Address for PCI Configuration Mechanism #1
  *

drivers/pci/probe.c

@@ -2477,6 +2477,7 @@ static void pci_init_capabilities(struct pci_dev *dev)
 	pci_dpc_init(dev);		/* Downstream Port Containment */
 	pci_rcec_init(dev);		/* Root Complex Event Collector */
 	pci_doe_init(dev);		/* Data Object Exchange */
+	pci_cma_init(dev);		/* Component Measurement & Auth */
 
 	pcie_report_downtraining(dev);
 	pci_init_reset_methods(dev);