[U-Boot,v2,03/16] efi_loader: add signature verification functions
diff mbox series

Message ID 20191126005120.31156-4-takahiro.akashi@linaro.org
State Superseded
Delegated to: Heinrich Schuchardt
Headers show
Series
  • efi_loader: add secure boot support
Related show

Commit Message

AKASHI Takahiro Nov. 26, 2019, 12:51 a.m. UTC
In this commit, implemented are a couple of helper functions which will be
used to materialize variable authentication as well as image authentication
in later patches.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
 include/efi_api.h              |  87 +++++
 include/efi_loader.h           |  72 ++++
 lib/efi_loader/Makefile        |   1 +
 lib/efi_loader/efi_signature.c | 584 +++++++++++++++++++++++++++++++++
 4 files changed, 744 insertions(+)
 create mode 100644 lib/efi_loader/efi_signature.c

Comments

Ilias Apalodimas Nov. 26, 2019, 11:55 a.m. UTC | #1
[...]
> +	/* verify signature */
> +		/* against digest */
> +		c = 0x31;
> +		regtmp[0].data = &c;
> +		regtmp[0].size = 1;

Is there a reason for '1' instea of sizeof(c)?

> +		regtmp[1].data = ps_info->authattrs;
> +		regtmp[1].size = ps_info->authattrs_len;
> +
> +
> +out:

Thanks
/Ilias
AKASHI Takahiro Nov. 27, 2019, 1:29 a.m. UTC | #2
On Tue, Nov 26, 2019 at 01:55:29PM +0200, Ilias Apalodimas wrote:
> [...]
> > +	/* verify signature */
> > +		/* against digest */
> > +		c = 0x31;
> > +		regtmp[0].data = &c;
> > +		regtmp[0].size = 1;
> 
> Is there a reason for '1' instea of sizeof(c)?

Yes, it explicitly says that we want to add *exact one byte* for
hash calculation here.

Thanks,
-Takahiro Akashi

> > +		regtmp[1].data = ps_info->authattrs;
> > +		regtmp[1].size = ps_info->authattrs_len;
> > +
> > +
> > +out:
> 
> Thanks
> /Ilias

Patch
diff mbox series

diff --git a/include/efi_api.h b/include/efi_api.h
index 22396172e15f..47f24fc90873 100644
--- a/include/efi_api.h
+++ b/include/efi_api.h
@@ -18,6 +18,7 @@ 
 
 #include <efi.h>
 #include <charset.h>
+#include <pe.h>
 
 #ifdef CONFIG_EFI_LOADER
 #include <asm/setjmp.h>
@@ -307,6 +308,10 @@  struct efi_runtime_services {
 	EFI_GUID(0x8be4df61, 0x93ca, 0x11d2, 0xaa, 0x0d, \
 		 0x00, 0xe0, 0x98, 0x03, 0x2b, 0x8c)
 
+#define EFI_IMAGE_SECURITY_DATABASE_GUID \
+	EFI_GUID(0xd719b2cb, 0x3d3a, 0x4596, 0xa3, 0xbc, \
+		 0xda, 0xd0, 0x0e, 0x67, 0x65, 0x6f)
+
 #define EFI_FDT_GUID \
 	EFI_GUID(0xb1b621d5, 0xf19c, 0x41a5, \
 		 0x83, 0x0b, 0xd9, 0x15, 0x2c, 0x69, 0xaa, 0xe0)
@@ -1616,4 +1621,86 @@  struct efi_unicode_collation_protocol {
 #define LOAD_OPTION_CATEGORY_BOOT	0x00000000
 #define LOAD_OPTION_CATEGORY_APP	0x00000100
 
+/* Certificate types in signature database */
+#define EFI_CERT_SHA256_GUID \
+	EFI_GUID(0xc1c41626, 0x504c, 0x4092, 0xac, 0xa9, \
+		 0x41, 0xf9, 0x36, 0x93, 0x43, 0x28)
+#define EFI_CERT_RSA2048_GUID \
+	EFI_GUID(0x3c5766e8, 0x269c, 0x4e34, 0xaa, 0x14, \
+		 0xed, 0x77, 0x6e, 0x85, 0xb3, 0xb6)
+#define EFI_CERT_X509_GUID \
+	EFI_GUID(0xa5c059a1, 0x94e4, 0x4aa7, 0x87, 0xb5, \
+		 0xab, 0x15, 0x5c, 0x2b, 0xf0, 0x72)
+#define EFI_CERT_X509_SHA256_GUID \
+	EFI_GUID(0x3bd2a492, 0x96c0, 0x4079, 0xb4, 0x20, \
+		 0xfc, 0xf9, 0x8e, 0xf1, 0x03, 0xed)
+#define EFI_CERT_TYPE_PKCS7_GUID \
+	EFI_GUID(0x4aafd29d, 0x68df, 0x49ee, 0x8a, 0xa9, \
+		 0x34, 0x7d, 0x37, 0x56, 0x65, 0xa7)
+
+/**
+ * win_certificate_uefi_guid - A certificate that encapsulates
+ * a GUID-specific signature
+ *
+ * @hdr:	Windows certificate header
+ * @cert_type:	Certificate type
+ * @cert_data:	Certificate data
+ */
+struct win_certificate_uefi_guid {
+	WIN_CERTIFICATE	hdr;
+	efi_guid_t	cert_type;
+	u8		cert_data[];
+} __attribute__((__packed__));
+
+/**
+ * efi_variable_authentication_2 - A time-based authentication method
+ * descriptor
+ *
+ * This structure describes an authentication information for
+ * a variable with EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS
+ * and should be included as part of a variable's value.
+ * Only EFI_CERT_TYPE_PKCS7_GUID is accepted.
+ *
+ * @time_stamp:	Descriptor's time stamp
+ * @auth_info:	Authentication info
+ */
+struct efi_variable_authentication_2 {
+	struct efi_time			 time_stamp;
+	struct win_certificate_uefi_guid auth_info;
+} __attribute__((__packed__));
+
+/**
+ * efi_signature_data - A format of signature
+ *
+ * This structure describes a single signature in signature database.
+ *
+ * @signature_owner:	Signature owner
+ * @signature_data:	Signature data
+ */
+struct efi_signature_data {
+	efi_guid_t	signature_owner;
+	u8		signature_data[];
+} __attribute__((__packed__));
+
+/**
+ * efi_signature_list - A format of signature database
+ *
+ * This structure describes a list of signatures with the same type.
+ * An authenticated variable's value is a concatenation of one or more
+ * efi_signature_list's.
+ *
+ * @signature_type:		Signature type
+ * @signature_list_size:	Size of signature list
+ * @signature_header_size:	Size of signature header
+ * @signature_size:		Size of signature
+ */
+struct efi_signature_list {
+	efi_guid_t	signature_type;
+	u32		signature_list_size;
+	u32		signature_header_size;
+	u32		signature_size;
+/*	u8		signature_header[signature_header_size]; */
+/*	struct efi_signature_data signatures[...][signature_size]; */
+} __attribute__((__packed__));
+
 #endif
diff --git a/include/efi_loader.h b/include/efi_loader.h
index 381da80cdce0..622bae6a6906 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -21,6 +21,7 @@  static inline int guidcmp(const void *g1, const void *g2)
 #if CONFIG_IS_ENABLED(EFI_LOADER)
 
 #include <linux/list.h>
+#include <linux/oid_registry.h>
 
 /* Maximum number of configuration tables */
 #define EFI_MAX_CONFIGURATION_TABLES 16
@@ -169,6 +170,11 @@  extern const efi_guid_t efi_guid_hii_config_routing_protocol;
 extern const efi_guid_t efi_guid_hii_config_access_protocol;
 extern const efi_guid_t efi_guid_hii_database_protocol;
 extern const efi_guid_t efi_guid_hii_string_protocol;
+/* GUIDs for authentication */
+extern const efi_guid_t efi_guid_image_security_database;
+extern const efi_guid_t efi_guid_sha256;
+extern const efi_guid_t efi_guid_cert_x509;
+extern const efi_guid_t efi_guid_cert_x509_sha256;
 
 extern unsigned int __efi_runtime_start, __efi_runtime_stop;
 extern unsigned int __efi_runtime_rel_start, __efi_runtime_rel_stop;
@@ -650,6 +656,72 @@  void efi_deserialize_load_option(struct efi_load_option *lo, u8 *data);
 unsigned long efi_serialize_load_option(struct efi_load_option *lo, u8 **data);
 efi_status_t efi_bootmgr_load(efi_handle_t *handle);
 
+#ifdef CONFIG_EFI_SECURE_BOOT
+#include <image.h>
+
+#define EFI_REGS_MAX 16 /* currently good enough */
+
+/**
+ * efi_image_regions - A list of memory regions
+ *
+ * @num:	Number of regions
+ * @reg:	array of regions
+ */
+struct efi_image_regions {
+	int			num;
+	struct image_region	reg[EFI_REGS_MAX];
+};
+
+/**
+ * efi_sig_data - A decoded data of struct efi_signature_data
+ *
+ * This structure represents an internal form of signature in
+ * signature database. A listed list may represent a signature list.
+ *
+ * @next:	Pointer to next entry
+ * @onwer:	Signature owner
+ * @data:	Pointer to signature data
+ * @size:	Size of signature data
+ */
+struct efi_sig_data {
+	struct efi_sig_data *next;
+	efi_guid_t owner;
+	void *data;
+	size_t size;
+};
+
+/**
+ * efi_signature_store - A decoded data of signature database
+ *
+ * This structure represents an internal form of signature database.
+ *
+ * @next:		Pointer to next entry
+ * @sig_type:		Signature type
+ * @sig_data_list:	Pointer to signature list
+ */
+struct efi_signature_store {
+	struct efi_signature_store *next;
+	efi_guid_t sig_type;
+	struct efi_sig_data *sig_data_list;
+};
+
+struct x509_certificate;
+struct pkcs7_message;
+
+bool efi_signature_verify_cert(struct x509_certificate *cert,
+			       struct efi_signature_store *dbx);
+bool efi_signature_verify_signers(struct pkcs7_message *msg,
+				  struct efi_signature_store *dbx);
+bool efi_signature_verify_with_sigdb(struct efi_image_regions *regs,
+				     struct pkcs7_message *msg,
+				  struct efi_signature_store *db,
+				  struct x509_certificate **cert);
+
+efi_status_t efi_image_region_add(struct efi_image_regions *regs,
+				  const void *start, const void *end,
+				  int nocheck);
+#endif /* CONFIG_EFI_SECURE_BOOT */
+
 #else /* CONFIG_IS_ENABLED(EFI_LOADER) */
 
 /* Without CONFIG_EFI_LOADER we don't have a runtime section, stub it out */
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index 7db406028618..3ffbfe78a46b 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -42,3 +42,4 @@  obj-$(CONFIG_PARTITIONS) += efi_disk.o
 obj-$(CONFIG_NET) += efi_net.o
 obj-$(CONFIG_GENERATE_ACPI_TABLE) += efi_acpi.o
 obj-$(CONFIG_GENERATE_SMBIOS_TABLE) += efi_smbios.o
+obj-y += efi_signature.o
diff --git a/lib/efi_loader/efi_signature.c b/lib/efi_loader/efi_signature.c
new file mode 100644
index 000000000000..87a39b790f67
--- /dev/null
+++ b/lib/efi_loader/efi_signature.c
@@ -0,0 +1,584 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2018 Patrick Wildt <patrick@blueri.se>
+ * Copyright (c) 2019 Linaro Limited, Author: AKASHI Takahiro
+ */
+
+#include <common.h>
+#include <charset.h>
+#include <efi_loader.h>
+#include <image.h>
+#include <hexdump.h>
+#include <malloc.h>
+#include <pe.h>
+#include <linux/compat.h>
+#include <linux/oid_registry.h>
+#include <u-boot/rsa.h>
+#include <u-boot/sha256.h>
+/*
+ * avoid duplicated inclusion:
+ * #include "../lib/crypto/x509_parser.h"
+ */
+#include "../lib/crypto/pkcs7_parser.h"
+
+const efi_guid_t efi_guid_image_security_database =
+		EFI_IMAGE_SECURITY_DATABASE_GUID;
+const efi_guid_t efi_guid_sha256 = EFI_CERT_SHA256_GUID;
+const efi_guid_t efi_guid_cert_rsa2048 = EFI_CERT_RSA2048_GUID;
+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;
+
+#ifdef CONFIG_EFI_SECURE_BOOT
+
+/**
+ * efi_hash_regions - calculate a hash value
+ * @regs:	List of regions
+ * @hash:	Pointer to a pointer to buffer holding a hash value
+ * @size:	Size of buffer to be returned
+ *
+ * Calculate a sha256 value of @regs and return a value in @hash.
+ *
+ * Return:	true on success, false on error
+ */
+static bool efi_hash_regions(struct efi_image_regions *regs, void **hash,
+			     size_t *size)
+{
+	*size = 0;
+	*hash = calloc(1, SHA256_SUM_LEN);
+	if (!*hash) {
+		debug("Out of memory\n");
+		return false;
+	}
+	*size = SHA256_SUM_LEN;
+
+	hash_calculate("sha256", regs->reg, regs->num, *hash);
+#ifdef DEBUG
+	debug("hash calculated:\n");
+	print_hex_dump("    ", DUMP_PREFIX_OFFSET, 16, 1,
+		       *hash, SHA256_SUM_LEN, false);
+#endif
+
+	return true;
+}
+
+/**
+ * efi_hash_msg_content - calculate a hash value of contentInfo
+ * @msg:	Signature
+ * @hash:	Pointer to a pointer to buffer holding a hash value
+ * @size:	Size of buffer to be returned
+ *
+ * Calculate a sha256 value of contentInfo in @msg and return a value in @hash.
+ *
+ * Return:	true on success, false on error
+ */
+static bool efi_hash_msg_content(struct pkcs7_message *msg, void **hash,
+				 size_t *size)
+{
+	struct image_region regtmp;
+
+	*size = 0;
+	*hash = calloc(1, SHA256_SUM_LEN);
+	if (!*hash) {
+		debug("Out of memory\n");
+		free(msg);
+		return false;
+	}
+	*size = SHA256_SUM_LEN;
+
+	regtmp.data = msg->data;
+	regtmp.size = msg->data_len;
+
+	hash_calculate("sha256", &regtmp, 1, *hash);
+#ifdef DEBUG
+	debug("hash calculated based on contentInfo:\n");
+	print_hex_dump("    ", DUMP_PREFIX_OFFSET, 16, 1,
+		       *hash, SHA256_SUM_LEN, false);
+#endif
+
+	return true;
+}
+
+/**
+ * efi_signature_verify - verify a signature with a certificate
+ * @regs:		List of regions to be authenticated
+ * @signed_info:	Pointer to PKCS7's signed_info
+ * @cert:		x509 certificate
+ *
+ * Signature pointed to by @signed_info against image pointed to by @regs
+ * is verified by a certificate pointed to by @cert.
+ * @signed_info holds a signature, including a message digest which is to be
+ * compared with a hash value calculated from @regs.
+ *
+ * Return:	true if signature is verified, false if not
+ */
+static bool efi_signature_verify(struct efi_image_regions *regs,
+				 struct pkcs7_message *msg,
+				 struct pkcs7_signed_info *ps_info,
+				 struct x509_certificate *cert)
+{
+	struct image_sign_info info;
+	struct image_region regtmp[2];
+	void *hash;
+	size_t size;
+	char c;
+	bool verified;
+
+	debug("%s: Enter, %p, %p, %p(issuer: %s, subject: %s)\n", __func__,
+	      regs, ps_info, cert, cert->issuer, cert->subject);
+
+	verified = false;
+
+	memset(&info, '\0', sizeof(info));
+	info.padding = image_get_padding_algo("pkcs-1.5");
+	/*
+	 * Note: image_get_[checksum|crypto]_algo takes an string
+	 * argument like "<checksum>,<crypto>"
+	 * TODO: support other hash algorithms
+	 */
+	if (!strcmp(ps_info->sig->hash_algo, "sha1")) {
+		info.checksum = image_get_checksum_algo("sha1,rsa2048");
+		info.name = "sha1,rsa2048";
+	} else if (!strcmp(ps_info->sig->hash_algo, "sha256")) {
+		info.checksum = image_get_checksum_algo("sha256,rsa2048");
+		info.name = "sha256,rsa2048";
+	} else {
+		debug("unknown msg digest algo: %s\n", ps_info->sig->hash_algo);
+		goto out;
+	}
+	info.crypto = image_get_crypto_algo(info.name);
+
+	info.key = cert->pub->key;
+	info.keylen = cert->pub->keylen;
+
+	/* verify signature */
+	debug("%s: crypto: %s, signature len:%x\n", __func__,
+	      info.name, ps_info->sig->s_size);
+	if (ps_info->aa_set & (1UL << sinfo_has_message_digest)) {
+		debug("%s: RSA verify authentication attribute\n", __func__);
+		/*
+		 * NOTE: This path will be executed only for
+		 * PE image authentication
+		 */
+
+		/* check if hash matches digest first */
+		debug("checking msg digest first, len:0x%x\n",
+		      ps_info->msgdigest_len);
+
+#ifdef DEBUG
+		debug("hash in database:\n");
+		print_hex_dump("    ", DUMP_PREFIX_OFFSET, 16, 1,
+			       ps_info->msgdigest, ps_info->msgdigest_len,
+			       false);
+#endif
+		/* against contentInfo first */
+		if ((msg->data && efi_hash_msg_content(msg, &hash, &size)) ||
+				/* for signed image */
+		    efi_hash_regions(regs, &hash, &size)) {
+				/* for authenticated variable */
+			if (ps_info->msgdigest_len != size ||
+			    memcmp(hash, ps_info->msgdigest, size)) {
+				debug("Digest doesn't match\n");
+				free(hash);
+				goto out;
+			}
+
+			free(hash);
+		} else {
+			debug("Digesting image failed\n");
+			goto out;
+		}
+
+		/* against digest */
+		c = 0x31;
+		regtmp[0].data = &c;
+		regtmp[0].size = 1;
+		regtmp[1].data = ps_info->authattrs;
+		regtmp[1].size = ps_info->authattrs_len;
+
+		if (!rsa_verify(&info, regtmp, 2,
+				ps_info->sig->s, ps_info->sig->s_size))
+			verified = true;
+	} else {
+		debug("%s: RSA verify content data\n", __func__);
+		/* against all data */
+		if (!rsa_verify(&info, regs->reg, regs->num,
+				ps_info->sig->s, ps_info->sig->s_size))
+			verified = true;
+	}
+
+out:
+	debug("%s: Exit, verified: %d\n", __func__, verified);
+	return verified;
+}
+
+/**
+ * efi_signature_verify_with_list - verify a signature with signature list
+ * @regs:		List of regions to be authenticated
+ * @msg:		Signature
+ * @signed_info:	Pointer to PKCS7's signed_info
+ * @siglist:		Signature list for certificates
+ * @valid_cert:		x509 certificate that verifies this signature
+ *
+ * Signature pointed to by @signed_info against image pointed to by @regs
+ * is verified by signature list pointed to by @siglist.
+ * Signature database is a simple concatenation of one or more
+ * signature list(s).
+ *
+ * Return:	true if signature is verified, false if not
+ */
+static
+bool efi_signature_verify_with_list(struct efi_image_regions *regs,
+				    struct pkcs7_message *msg,
+				    struct pkcs7_signed_info *signed_info,
+				    struct efi_signature_store *siglist,
+				    struct x509_certificate **valid_cert)
+{
+	struct x509_certificate *cert;
+	struct efi_sig_data *sig_data;
+	bool verified = false;
+
+	debug("%s: Enter, %p, %p, %p, %p\n", __func__,
+	      regs, signed_info, siglist, valid_cert);
+
+	if (!signed_info) {
+		void *hash;
+		size_t size;
+
+		debug("%s: unsigned image\n", __func__);
+		/*
+		 * verify based on calculated hash value
+		 * TODO: support other hash algorithms
+		 */
+		if (guidcmp(&siglist->sig_type, &efi_guid_sha256)) {
+			debug("Digest algorithm is not supported: %pUl\n",
+			      &siglist->sig_type);
+			goto out;
+		}
+
+		if (!efi_hash_regions(regs, &hash, &size)) {
+			debug("Digesting unsigned image failed\n");
+			goto out;
+		}
+
+		/* go through the list */
+		for (sig_data = siglist->sig_data_list; sig_data;
+		     sig_data = sig_data->next) {
+#ifdef DEBUG
+			debug("Msg digest in database:\n");
+			print_hex_dump("    ", DUMP_PREFIX_OFFSET, 16, 1,
+				       sig_data->data, sig_data->size, false);
+#endif
+			if ((sig_data->size == size) &&
+			    !memcmp(sig_data->data, hash, size)) {
+				verified = true;
+				free(hash);
+				goto out;
+			}
+		}
+		free(hash);
+		goto out;
+	}
+
+	debug("%s: signed image\n", __func__);
+	if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509)) {
+		debug("Signature type is not supported: %pUl\n",
+		      &siglist->sig_type);
+		goto out;
+	}
+
+	/* go through the list */
+	for (sig_data = siglist->sig_data_list; sig_data;
+	     sig_data = sig_data->next) {
+		/* TODO: support owner check based on policy */
+
+		cert = x509_cert_parse(sig_data->data, sig_data->size);
+		if (IS_ERR(cert)) {
+			debug("Parsing x509 certificate failed\n");
+			goto out;
+		}
+
+		verified = efi_signature_verify(regs, msg, signed_info, cert);
+
+		if (verified) {
+			if (valid_cert)
+				*valid_cert = cert;
+			else
+				x509_free_certificate(cert);
+			break;
+		} else {
+			x509_free_certificate(cert);
+		}
+	}
+
+out:
+	debug("%s: Exit, verified: %d\n", __func__, verified);
+	return verified;
+}
+
+/**
+ * efi_signature_verify_with_sigdb - verify a signature with db
+ * @regs:	List of regions to be authenticated
+ * @msg:	Signature
+ * @db:		Signature database for trusted certificates
+ * @cert:	x509 certificate that verifies this signature
+ *
+ * Signature pointed to by @msg against image pointed to by @regs
+ * is verified by signature database pointed to by @db.
+ *
+ * Return:	true if signature is verified, false if not
+ */
+bool efi_signature_verify_with_sigdb(struct efi_image_regions *regs,
+				     struct pkcs7_message *msg,
+				     struct efi_signature_store *db,
+				     struct x509_certificate **cert)
+{
+	struct pkcs7_signed_info *info;
+	struct efi_signature_store *siglist;
+	bool verified = false;
+
+	debug("%s: Enter, %p, %p, %p, %p\n", __func__, regs, msg, db, cert);
+
+	if (!db)
+		goto out;
+
+	if (!db->sig_data_list)
+		goto out;
+
+	/* for unsigned image */
+	if (!msg) {
+		debug("%s: Verify unsigned image with db\n", __func__);
+		for (siglist = db; siglist; siglist = siglist->next)
+			if (efi_signature_verify_with_list(regs, NULL, NULL,
+							   siglist, cert)) {
+				verified = true;
+				goto out;
+			}
+
+		goto out;
+	}
+
+	/* for signed image or variable */
+	debug("%s: Verify signed image with db\n", __func__);
+	for (info = msg->signed_infos; info; info = info->next) {
+		debug("Signed Info: digest algo: %s, pkey algo: %s\n",
+		      info->sig->hash_algo, info->sig->pkey_algo);
+
+		for (siglist = db; siglist; siglist = siglist->next) {
+			if (efi_signature_verify_with_list(regs, msg, info,
+							   siglist, cert)) {
+				verified = true;
+				goto out;
+			}
+		}
+	}
+
+out:
+	debug("%s: Exit, verified: %d\n", __func__, verified);
+	return verified;
+}
+
+/**
+ * efi_search_siglist - search signature list for a certificate
+ * @cert:	x509 certificate
+ * @siglist:	Signature list
+ * @revoc_time:	Pointer to buffer for revocation time
+ *
+ * Search signature list pointed to by @siglist and find a certificate
+ * pointed to by @cert.
+ * If found, revocation time that is specified in signature database is
+ * returned in @revoc_time.
+ *
+ * Return:	true if certificate is found, false if not
+ */
+static bool efi_search_siglist(struct x509_certificate *cert,
+			       struct efi_signature_store *siglist,
+			       time64_t *revoc_time)
+{
+	struct image_region reg[1];
+	void *hash = NULL, *msg = NULL;
+	struct efi_sig_data *sig_data;
+	bool found = false;
+
+	/* can be null */
+	if (!siglist->sig_data_list)
+		return false;
+
+	if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509_sha256)) {
+		/* TODO: other hash algos */
+		debug("Certificate's digest type is not supported: %pUl\n",
+		      &siglist->sig_type);
+		goto out;
+	}
+
+	/* calculate hash of TBSCertificate */
+	msg = calloc(1, SHA256_SUM_LEN);
+	if (!msg) {
+		debug("Out of memory\n");
+		goto out;
+	}
+
+	hash = calloc(1, SHA256_SUM_LEN);
+	if (!hash) {
+		debug("Out of memory\n");
+		goto out;
+	}
+
+	reg[0].data = cert->tbs;
+	reg[0].size = cert->tbs_size;
+	hash_calculate("sha256", reg, 1, msg);
+
+	/* go through signature list */
+	for (sig_data = siglist->sig_data_list; sig_data;
+	     sig_data = sig_data->next) {
+		/*
+		 * struct efi_cert_x509_sha256 {
+		 *	u8 tbs_hash[256/8];
+		 *	time64_t revocation_time;
+		 * };
+		 */
+		if ((sig_data->size == SHA256_SUM_LEN) &&
+		    !memcmp(sig_data->data, hash, SHA256_SUM_LEN)) {
+			memcpy(revoc_time, sig_data->data + SHA256_SUM_LEN,
+			       sizeof(*revoc_time));
+			found = true;
+			goto out;
+		}
+	}
+
+out:
+	free(hash);
+	free(msg);
+
+	return found;
+}
+
+/**
+ * efi_signature_verify_cert - verify a certificate with dbx
+ * @cert:	x509 certificate
+ * @dbx:	Signature database
+ *
+ * Search signature database pointed to by @dbx and find a certificate
+ * pointed to by @cert.
+ * This function is expected to be used against "dbx".
+ *
+ * Return:	true if a certificate is not rejected, false otherwise.
+ */
+bool efi_signature_verify_cert(struct x509_certificate *cert,
+			       struct efi_signature_store *dbx)
+{
+	struct efi_signature_store *siglist;
+	time64_t revoc_time;
+	bool found = false;
+
+	debug("%s: Enter, %p, %p\n", __func__, dbx, cert);
+
+	if (!cert)
+		return false;
+
+	for (siglist = dbx; siglist; siglist = siglist->next) {
+		if (efi_search_siglist(cert, siglist, &revoc_time)) {
+			/* TODO */
+			/* compare signing time with revocation time */
+
+			found = true;
+			break;
+		}
+	}
+
+	debug("%s: Exit, verified: %d\n", __func__, !found);
+	return !found;
+}
+
+/**
+ * efi_signature_verify_signers - verify signers' certificates with dbx
+ * @msg:	Signature
+ * @dbx:	Signature database
+ *
+ * Determine if any of signers' certificates in @msg may be verified
+ * by any of certificates in signature database pointed to by @dbx.
+ * This function is expected to be used against "dbx".
+ *
+ * Return:	true if none of certificates is rejected, false otherwise.
+ */
+bool efi_signature_verify_signers(struct pkcs7_message *msg,
+				  struct efi_signature_store *dbx)
+{
+	struct pkcs7_signed_info *info;
+	bool found = false;
+
+	debug("%s: Enter, %p, %p\n", __func__, msg, dbx);
+
+	if (!msg)
+		goto out;
+
+	for (info = msg->signed_infos; info; info = info->next) {
+		if (info->signer &&
+		    !efi_signature_verify_cert(info->signer, dbx)) {
+			found = true;
+			goto out;
+		}
+	}
+out:
+	debug("%s: Exit, verified: %d\n", __func__, !found);
+	return !found;
+}
+
+/**
+ * efi_image_region_add - add an entry of region
+ * @regs:	Pointer to array of regions
+ * @start:	Start address of region
+ * @end:	End address of region
+ * @nocheck:	flag against overlapped regions
+ *
+ * Take one entry of region [@start, @end] and append it to the list
+ * pointed to by @regs. If @nocheck is false, overlapping among entries
+ * will be checked first.
+ *
+ * Return:	0 on success, status code (negative) on error
+ */
+efi_status_t efi_image_region_add(struct efi_image_regions *regs,
+				  const void *start, const void *end,
+				  int nocheck)
+{
+	struct image_region *reg;
+	int i, j;
+
+	if (regs->num >= EFI_REGS_MAX) {
+		debug("%s: no more room for regions\n", __func__);
+		return EFI_OUT_OF_RESOURCES;
+	}
+
+	if (end < start)
+		return EFI_INVALID_PARAMETER;
+
+	for (i = 0; i < regs->num; i++) {
+		reg = &regs->reg[i];
+		if (nocheck)
+			continue;
+
+		if (start > reg->data + reg->size)
+			continue;
+
+		if ((start >= reg->data && start < reg->data + reg->size) ||
+		    (end > reg->data && end < reg->data + reg->size)) {
+			debug("%s: new region already part of another\n",
+			      __func__);
+			return EFI_INVALID_PARAMETER;
+		}
+
+		if (start < reg->data && end < reg->data + reg->size) {
+			for (j = regs->num - 1; j >= i; j--)
+				memcpy(&regs->reg[j], &regs->reg[j + 1],
+				       sizeof(*reg));
+			break;
+		}
+	}
+
+	reg = &regs->reg[i];
+	reg->data = start;
+	reg->size = end - start;
+	regs->num++;
+
+	return EFI_SUCCESS;
+}
+#endif /* CONFIG_EFI_SECURE_BOOT */