PCIe r6.1 sec 6.31.3 stipulates requirements for X.509 Leaf Certificates presented by devices, in particular the presence of a Subject Alternative Name extension with a name that encodes the Vendor ID, Device ID, Device Serial Number, etc. This prevents a mismatch between the device identity in Config Space and the certificate. A device cannot misappropriate a certificate from a different device without also spoofing Config Space. As a corollary, it cannot dupe an arbitrary driver into binding to it. (Only those which bind to the device identity in the Subject Alternative Name work.) Parse the Subject Alternative Name using a small ASN.1 module and validate its contents. The theory of operation is explained in a code comment at the top of the newly added cma-x509.c. This functionality is introduced in a separate commit on top of basic CMA-SPDM support to split the code into digestible, reviewable chunks. The CMA OID added here is taken from the official OID Repository (it's not documented in the PCIe Base Spec): https://oid-rep.orange-labs.fr/get/2.23.147 Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> --- drivers/pci/Makefile | 4 +- drivers/pci/cma-x509.c | 119 +++++++++++++++++++++++++++++++++++ drivers/pci/cma.asn1 | 36 +++++++++++ drivers/pci/cma.c | 3 +- drivers/pci/pci.h | 2 + include/linux/oid_registry.h | 3 + include/linux/spdm.h | 6 +- lib/spdm_requester.c | 14 ++++- 8 files changed, 183 insertions(+), 4 deletions(-) create mode 100644 drivers/pci/cma-x509.c create mode 100644 drivers/pci/cma.asn1 diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile index e0705b82690b..a18812b8832b 100644 --- a/drivers/pci/Makefile +++ b/drivers/pci/Makefile @@ -34,7 +34,9 @@ obj-$(CONFIG_VGA_ARB) += vgaarb.o obj-$(CONFIG_PCI_DOE) += doe.o obj-$(CONFIG_PCI_DYNAMIC_OF_NODES) += of_property.o -obj-$(CONFIG_PCI_CMA) += cma.o +obj-$(CONFIG_PCI_CMA) += cma.o cma-x509.o cma.asn1.o +$(obj)/cma-x509.o: $(obj)/cma.asn1.h +$(obj)/cma.asn1.o: $(obj)/cma.asn1.c $(obj)/cma.asn1.h # Endpoint library must be initialized before its users obj-$(CONFIG_PCI_ENDPOINT) += endpoint/ diff --git a/drivers/pci/cma-x509.c b/drivers/pci/cma-x509.c new file mode 100644 index 000000000000..614590303b38 --- /dev/null +++ b/drivers/pci/cma-x509.c @@ -0,0 +1,119 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Component Measurement and Authentication (CMA-SPDM, PCIe r6.1 sec 6.31) + * + * The spdm_requester.c library calls pci_cma_validate() to check requirements + * for X.509 Leaf Certificates per PCIe r6.1 sec 6.31.3. + * + * It parses the Subject Alternative Name using the ASN.1 module cma.asn1, + * which calls pci_cma_note_oid() and pci_cma_note_san() to compare an + * OtherName against the expected name. + * + * The expected name is constructed beforehand by pci_cma_construct_san(). + * + * Copyright (C) 2023 Intel Corporation + */ + +#define dev_fmt(fmt) "CMA: " fmt + +#include <keys/x509-parser.h> +#include <linux/asn1_decoder.h> +#include <linux/oid_registry.h> +#include <linux/pci.h> + +#include "cma.asn1.h" +#include "pci.h" + +#define CMA_NAME_MAX sizeof("Vendor=1234:Device=1234:CC=123456:" \ + "REV=12:SSVID=1234:SSID=1234:1234567890123456") + +struct pci_cma_x509_context { + struct pci_dev *pdev; + enum OID last_oid; + char expected_name[CMA_NAME_MAX]; + unsigned int expected_len; + unsigned int found:1; +}; + +int pci_cma_note_oid(void *context, size_t hdrlen, unsigned char tag, + const void *value, size_t vlen) +{ + struct pci_cma_x509_context *ctx = context; + + ctx->last_oid = look_up_OID(value, vlen); + + return 0; +} + +int pci_cma_note_san(void *context, size_t hdrlen, unsigned char tag, + const void *value, size_t vlen) +{ + struct pci_cma_x509_context *ctx = context; + + /* These aren't the drOIDs we're looking for. */ + if (ctx->last_oid != OID_CMA) + return 0; + + if (tag != ASN1_UTF8STR || + vlen != ctx->expected_len || + memcmp(value, ctx->expected_name, vlen) != 0) { + pci_err(ctx->pdev, "Invalid X.509 Subject Alternative Name\n"); + return -EINVAL; + } + + ctx->found = true; + + return 0; +} + +static unsigned int pci_cma_construct_san(struct pci_dev *pdev, char *name) +{ + unsigned int len; + u64 serial; + + len = snprintf(name, CMA_NAME_MAX, + "Vendor=%04hx:Device=%04hx:CC=%06x:REV=%02hhx", + pdev->vendor, pdev->device, pdev->class, pdev->revision); + + if (pdev->hdr_type == PCI_HEADER_TYPE_NORMAL) + len += snprintf(name + len, CMA_NAME_MAX - len, + ":SSVID=%04hx:SSID=%04hx", + pdev->subsystem_vendor, pdev->subsystem_device); + + serial = pci_get_dsn(pdev); + if (serial) + len += snprintf(name + len, CMA_NAME_MAX - len, + ":%016llx", serial); + + return len; +} + +int pci_cma_validate(struct device *dev, struct x509_certificate *leaf_cert) +{ + struct pci_dev *pdev = to_pci_dev(dev); + struct pci_cma_x509_context ctx; + int ret; + + if (!leaf_cert->raw_san) { + pci_err(pdev, "Missing X.509 Subject Alternative Name\n"); + return -EINVAL; + } + + ctx.pdev = pdev; + ctx.found = false; + ctx.expected_len = pci_cma_construct_san(pdev, ctx.expected_name); + + ret = asn1_ber_decoder(&cma_decoder, &ctx, leaf_cert->raw_san, + leaf_cert->raw_san_size); + if (ret == -EBADMSG || ret == -EMSGSIZE) + pci_err(pdev, "Malformed X.509 Subject Alternative Name\n"); + if (ret < 0) + return ret; + + if (!ctx.found) { + pci_err(pdev, "Missing X.509 OtherName with CMA OID\n"); + return -EINVAL; + } + + return 0; +} diff --git a/drivers/pci/cma.asn1 b/drivers/pci/cma.asn1 new file mode 100644 index 000000000000..10f90e107009 --- /dev/null +++ b/drivers/pci/cma.asn1 @@ -0,0 +1,36 @@ +-- Component Measurement and Authentication (CMA-SPDM, PCIe r6.1 sec 6.31.3) +-- X.509 Subject Alternative Name (RFC 5280 sec 4.2.1.6) +-- +-- https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.6 +-- +-- The ASN.1 module in RFC 5280 appendix A.1 uses EXPLICIT TAGS whereas the one +-- in appendix A.2 uses IMPLICIT TAGS. The kernel's simplified asn1_compiler.c +-- always uses EXPLICIT TAGS, hence this ASN.1 module differs from RFC 5280 in +-- that it adds IMPLICIT to definitions from appendix A.2 (such as OtherName) +-- and omits EXPLICIT in those definitions. + +SubjectAltName ::= GeneralNames + +GeneralNames ::= SEQUENCE OF GeneralName + +GeneralName ::= CHOICE { + otherName [0] IMPLICIT OtherName, + rfc822Name [1] IMPLICIT IA5String, + dNSName [2] IMPLICIT IA5String, + x400Address [3] ANY, + directoryName [4] ANY, + ediPartyName [5] IMPLICIT EDIPartyName, + uniformResourceIdentifier [6] IMPLICIT IA5String, + iPAddress [7] IMPLICIT OCTET STRING, + registeredID [8] IMPLICIT OBJECT IDENTIFIER + } + +OtherName ::= SEQUENCE { + type-id OBJECT IDENTIFIER ({ pci_cma_note_oid }), + value [0] ANY ({ pci_cma_note_san }) + } + +EDIPartyName ::= SEQUENCE { + nameAssigner [0] ANY OPTIONAL, + partyName [1] ANY + } diff --git a/drivers/pci/cma.c b/drivers/pci/cma.c index 06e5846325e3..012190c54ab6 100644 --- a/drivers/pci/cma.c +++ b/drivers/pci/cma.c @@ -64,7 +64,8 @@ void pci_cma_init(struct pci_dev *pdev) return; pdev->spdm_state = spdm_create(&pdev->dev, pci_doe_transport, doe, - PCI_DOE_MAX_PAYLOAD, pci_cma_keyring); + PCI_DOE_MAX_PAYLOAD, pci_cma_keyring, + pci_cma_validate); if (!pdev->spdm_state) { return; } diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h index bd80a0369c9c..6c4755a2c91c 100644 --- a/drivers/pci/pci.h +++ b/drivers/pci/pci.h @@ -325,6 +325,8 @@ static inline void pci_doe_disconnected(struct pci_dev *pdev) { } #ifdef CONFIG_PCI_CMA void pci_cma_init(struct pci_dev *pdev); void pci_cma_destroy(struct pci_dev *pdev); +struct x509_certificate; +int pci_cma_validate(struct device *dev, struct x509_certificate *leaf_cert); #else static inline void pci_cma_init(struct pci_dev *pdev) { } static inline void pci_cma_destroy(struct pci_dev *pdev) { } diff --git a/include/linux/oid_registry.h b/include/linux/oid_registry.h index f86a08ba0207..cafec7111473 100644 --- a/include/linux/oid_registry.h +++ b/include/linux/oid_registry.h @@ -141,6 +141,9 @@ enum OID { OID_TPMImportableKey, /* 2.23.133.10.1.4 */ OID_TPMSealedData, /* 2.23.133.10.1.5 */ + /* PCI */ + OID_CMA, /* 2.23.147 */ + OID__NR }; diff --git a/include/linux/spdm.h b/include/linux/spdm.h index e824063793a7..69a83bc2eb41 100644 --- a/include/linux/spdm.h +++ b/include/linux/spdm.h @@ -17,14 +17,18 @@ struct key; struct device; struct spdm_state; +struct x509_certificate; typedef int (spdm_transport)(void *priv, struct device *dev, const void *request, size_t request_sz, void *response, size_t response_sz); +typedef int (spdm_validate)(struct device *dev, + struct x509_certificate *leaf_cert); + struct spdm_state *spdm_create(struct device *dev, spdm_transport *transport, void *transport_priv, u32 transport_sz, - struct key *keyring); + struct key *keyring, spdm_validate *validate); int spdm_authenticate(struct spdm_state *spdm_state); diff --git a/lib/spdm_requester.c b/lib/spdm_requester.c index 407041036599..b2af2074ba6f 100644 --- a/lib/spdm_requester.c +++ b/lib/spdm_requester.c @@ -489,6 +489,7 @@ static int spdm_err(struct device *dev, struct spdm_error_rsp *rsp) * responder's signatures. * @root_keyring: Keyring against which to check the first certificate in * responder's certificate chain. + * @validate: Function to validate additional leaf certificate requirements. */ struct spdm_state { struct mutex lock; @@ -520,6 +521,7 @@ struct spdm_state { /* Certificates */ struct public_key *leaf_key; struct key *root_keyring; + spdm_validate *validate; }; static int __spdm_exchange(struct spdm_state *spdm_state, @@ -1003,6 +1005,13 @@ static int spdm_validate_cert_chain(struct spdm_state *spdm_state, u8 slot, } prev = NULL; + + if (spdm_state->validate) { + rc = spdm_state->validate(spdm_state->dev, cert); + if (rc) + goto err_free_cert; + } + spdm_state->leaf_key = cert->pub; cert->pub = NULL; @@ -1447,12 +1456,14 @@ EXPORT_SYMBOL_GPL(spdm_authenticated); * @transport_priv: Transport private data * @transport_sz: Maximum message size the transport is capable of (in bytes) * @keyring: Trusted root certificates + * @validate: Function to validate additional leaf certificate requirements + * (optional, may be %NULL) * * Returns a pointer to the allocated SPDM session state or NULL on error. */ struct spdm_state *spdm_create(struct device *dev, spdm_transport *transport, void *transport_priv, u32 transport_sz, - struct key *keyring) + struct key *keyring, spdm_validate *validate) { struct spdm_state *spdm_state = kzalloc(sizeof(*spdm_state), GFP_KERNEL); @@ -1464,6 +1475,7 @@ struct spdm_state *spdm_create(struct device *dev, spdm_transport *transport, spdm_state->transport_priv = transport_priv; spdm_state->transport_sz = transport_sz; spdm_state->root_keyring = keyring; + spdm_state->validate = validate; mutex_init(&spdm_state->lock); -- 2.40.1
