[PATCH v4 03/16] efi_loader: add signature verification functions

[Heinrich Schuchardt <xypron.glpk@gmx.de>]

On 12/18/19 1:44 AM, AKASHI Takahiro wrote:
> 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
>
> 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..3ca68f9bbb6e 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

This constraint surrounds the whole code. So, please, move the
constraint to the Makefile.

Best regards

Heinrich

> +#include <image.h>
> +
> +/**
> + * efi_image_regions - A list of memory regions
> + *
> + * @max:	Maximum number of regions
> + * @num:	Number of regions
> + * @reg:	array of regions
> + */
> +struct efi_image_regions {
> +	int			max;
> +	int			num;
> +	struct image_region	reg[];
> +};
> +
> +/**
> + * 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..823d3311e010
> --- /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 >= 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 */
>