efi: capsule: Add support for uefi capsule authentication

Add support for authenticating uefi capsules. Most of the signature
verification functionality is shared with the uefi secure boot
feature.

The root certificate containing the public key used for the signature
verification is stored as part of the device tree blob. The root
certificate is stored as an efi signature list(esl) file -- this file
contains the x509 certificate which is the root certificate.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>

board/emulation/common/Makefile

@@ -2,3 +2,4 @@
 
 obj-$(CONFIG_SYS_MTDPARTS_RUNTIME) += qemu_mtdparts.o
 obj-$(CONFIG_SET_DFU_ALT_INFO) += qemu_dfu.o
+obj-$(CONFIG_EFI_CAPSULE_FIRMWARE_MANAGEMENT) += qemu_capsule.o

board/emulation/common/qemu_capsule.c

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2020 Linaro Limited
+ */
+
+#include <common.h>
+#include <efi_api.h>
+#include <efi_loader.h>
+#include <env.h>
+#include <fdtdec.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+int efi_get_public_key_data(void **pkey, efi_uintn_t *pkey_len)
+{
+	const void *fdt_blob = gd->fdt_blob;
+	const void *blob;
+	const char *cnode_name = "capsule-key";
+	const char *snode_name = "signature";
+	int sig_node;
+	int len;
+
+	sig_node = fdt_subnode_offset(fdt_blob, 0, snode_name);
+	if (sig_node < 0) {
+		EFI_PRINT("Unable to get signature node offset\n");
+		return -FDT_ERR_NOTFOUND;
+	}
+
+	blob = fdt_getprop(fdt_blob, sig_node, cnode_name, &len);
+
+	if (!blob || len < 0) {
+		EFI_PRINT("Unable to get capsule-key value\n");
+		*pkey = NULL;
+		*pkey_len = 0;
+		return -FDT_ERR_NOTFOUND;
+	}
+
+	*pkey = (void *)blob;
+	*pkey_len = len;
+
+	return 0;
+}
+
+bool efi_capsule_auth_enabled(void)
+{
+	return env_get("capsule_authentication_enabled") != NULL ?
+		true : false;
+}

include/efi_api.h

@@ -1812,6 +1812,24 @@ struct efi_variable_authentication_2 {
 	struct win_certificate_uefi_guid auth_info;
 } __attribute__((__packed__));
 
+/**
+ * efi_firmware_image_authentication - Capsule authentication method
+ * descriptor
+ *
+ * This structure describes an authentication information for
+ * a capsule with IMAGE_ATTRIBUTE_AUTHENTICATION_REQUIRED set
+ * and should be included as part of the capsule.
+ * Only EFI_CERT_TYPE_PKCS7_GUID is accepted.
+ *
+ * @monotonic_count: Count to prevent replay
+ * @auth_info: Authentication info
+ */
+struct efi_firmware_image_authentication {
+	uint64_t monotonic_count;
+	struct win_certificate_uefi_guid auth_info;
+} __attribute__((__packed__));
+
+
 /**
  * efi_signature_data - A format of signature
  *

include/efi_loader.h

@@ -819,6 +819,8 @@ struct efi_signature_store *efi_sigstore_parse_sigdb(u16 *name);
 
 bool efi_secure_boot_enabled(void);
 
+bool efi_capsule_auth_enabled(void);
+
 bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp,
 		     WIN_CERTIFICATE **auth, size_t *auth_len);
 
@@ -847,6 +849,10 @@ efi_status_t EFIAPI efi_query_capsule_caps(
 		u64 *maximum_capsule_size,
 		u32 *reset_type);
 
+efi_status_t efi_capsule_authenticate(const void *capsule,
+				      efi_uintn_t capsule_size,
+				      void **image, efi_uintn_t *image_size);
+
 #define EFI_CAPSULE_DIR L"\\EFI\\UpdateCapsule\\"
 
 /* Hook at initialization */

lib/efi_loader/Kconfig

@@ -153,6 +153,23 @@ config EFI_CAPSULE_FIRMWARE_MANAGEMENT
 	  Select this option if you want to enable capsule-based
 	  firmware update using Firmware Management Protocol.
 
+config EFI_CAPSULE_AUTHENTICATE
+	bool "Update Capsule authentication"
+	depends on EFI_CAPSULE_FIRMWARE
+	depends on EFI_CAPSULE_ON_DISK
+	depends on EFI_CAPSULE_FIRMWARE_MANAGEMENT
+	select SHA256
+	select RSA
+	select RSA_VERIFY
+	select RSA_VERIFY_WITH_PKEY
+	select X509_CERTIFICATE_PARSER
+	select PKCS7_MESSAGE_PARSER
+	select PKCS7_VERIFY
+	default n
+	help
+	  Select this option if you want to enable capsule
+	  authentication
+
 config EFI_CAPSULE_FIRMWARE_FIT
 	bool "FMP driver for FIT image"
 	depends on EFI_CAPSULE_FIRMWARE_MANAGEMENT

lib/efi_loader/efi_capsule.c

@@ -14,6 +14,10 @@
 #include <mapmem.h>
 #include <sort.h>
 
+#include <crypto/pkcs7.h>
+#include <crypto/pkcs7_parser.h>
+#include <linux/err.h>
+
 const efi_guid_t efi_guid_capsule_report = EFI_CAPSULE_REPORT_GUID;
 static const efi_guid_t efi_guid_firmware_management_capsule_id =
 		EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID;
@@ -191,6 +195,124 @@ skip:
 	return NULL;
 }
 
+#if defined(CONFIG_EFI_CAPSULE_AUTHENTICATE)
+
+const efi_guid_t efi_guid_capsule_root_cert_guid =
+	EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID;
+
+__weak int efi_get_public_key_data(void **pkey, efi_uintn_t *pkey_len)
+{
+	/* The platform is supposed to provide
+	 * a method for getting the public key
+	 * stored in the form of efi signature
+	 * list
+	 */
+	return 0;
+}
+
+efi_status_t efi_capsule_authenticate(const void *capsule, efi_uintn_t capsule_size,
+				      void **image, efi_uintn_t *image_size)
+{
+	u8 *buf;
+	int ret;
+	void *fdt_pkey, *pkey;
+	efi_uintn_t pkey_len;
+	uint64_t monotonic_count;
+	struct efi_signature_store *truststore;
+	struct pkcs7_message *capsule_sig;
+	struct efi_image_regions *regs;
+	struct efi_firmware_image_authentication *auth_hdr;
+	efi_status_t status;
+
+	status = EFI_SECURITY_VIOLATION;
+	capsule_sig = NULL;
+	truststore = NULL;
+	regs = NULL;
+
+	/* Sanity checks */
+	if (capsule == NULL || capsule_size == 0)
+		goto out;
+
+	auth_hdr = (struct efi_firmware_image_authentication *)capsule;
+	if (capsule_size < sizeof(*auth_hdr))
+		goto out;
+
+	if (auth_hdr->auth_info.hdr.dwLength <=
+	    offsetof(struct win_certificate_uefi_guid, cert_data))
+		goto out;
+
+	if (guidcmp(&auth_hdr->auth_info.cert_type, &efi_guid_cert_type_pkcs7))
+		goto out;
+
+	*image = (uint8_t *)capsule + sizeof(auth_hdr->monotonic_count) +
+		auth_hdr->auth_info.hdr.dwLength;
+	*image_size = capsule_size - auth_hdr->auth_info.hdr.dwLength -
+		sizeof(auth_hdr->monotonic_count);
+	memcpy(&monotonic_count, &auth_hdr->monotonic_count,
+	       sizeof(monotonic_count));
+
+	/* data to be digested */
+	regs = calloc(sizeof(*regs) + sizeof(struct image_region) * 2, 1);
+	if (!regs)
+		goto out;
+
+	regs->max = 2;
+	efi_image_region_add(regs, (uint8_t *)*image,
+			     (uint8_t *)*image + *image_size, 1);
+
+	efi_image_region_add(regs, (uint8_t *)&monotonic_count,
+			     (uint8_t *)&monotonic_count + sizeof(monotonic_count),
+			     1);
+
+	capsule_sig = efi_parse_pkcs7_header(auth_hdr->auth_info.cert_data,
+					     auth_hdr->auth_info.hdr.dwLength
+					     - sizeof(auth_hdr->auth_info),
+					     &buf);
+	if (IS_ERR(capsule_sig)) {
+		debug("Parsing variable's pkcs7 header failed\n");
+		capsule_sig = NULL;
+		goto out;
+	}
+
+	ret = efi_get_public_key_data(&fdt_pkey, &pkey_len);
+	if (ret < 0)
+		goto out;
+
+	pkey = malloc(pkey_len);
+	if (!pkey)
+		goto out;
+
+	memcpy(pkey, fdt_pkey, pkey_len);
+	truststore = efi_build_signature_store(pkey, pkey_len);
+	if (!truststore)
+		goto out;
+
+	/* verify signature */
+	if (efi_signature_verify(regs, capsule_sig, truststore, NULL)) {
+		debug("Verified\n");
+	} else {
+		debug("Verifying variable's signature failed\n");
+		goto out;
+	}
+
+	status = EFI_SUCCESS;
+
+out:
+	efi_sigstore_free(truststore);
+	pkcs7_free_message(capsule_sig);
+	free(regs);
+
+	return status;
+}
+#else
+efi_status_t efi_capsule_authenticate(const void *capsule, efi_uintn_t capsule_size,
+				      void **image, efi_uintn_t *image_size)
+{
+	return EFI_UNSUPPORTED;
+}
+#endif /* CONFIG_EFI_CAPSULE_AUTHENTICATE */
+
+
 /**
  * efi_capsule_update_firmware - update firmware from capsule
  * @capsule_data:	Capsule

lib/efi_loader/efi_signature.c

@@ -26,7 +26,7 @@ const efi_guid_t efi_guid_cert_x509 = EFI_CERT_X509_GUID;
 const efi_guid_t efi_guid_cert_x509_sha256 = EFI_CERT_X509_SHA256_GUID;
 const efi_guid_t efi_guid_cert_type_pkcs7 = EFI_CERT_TYPE_PKCS7_GUID;
 
-#ifdef CONFIG_EFI_SECURE_BOOT
+#if defined(CONFIG_EFI_SECURE_BOOT) || defined(CONFIG_EFI_CAPSULE_AUTHENTICATE)
 static u8 pkcs7_hdr[] = {
 	/* SEQUENCE */
 	0x30, 0x82, 0x05, 0xc7,
@@ -846,4 +846,4 @@ struct efi_signature_store *efi_sigstore_parse_sigdb(u16 *name)
 
 	return efi_build_signature_store(db, db_size);
 }
-#endif /* CONFIG_EFI_SECURE_BOOT */
+#endif /* CONFIG_EFI_SECURE_BOOT || CONFIG_EFI_CAPSULE_AUTHENTICATE */