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![AKASHI Takahiro](/assets/img/avatar_default.png)
Under the current implementation, all the signatures, if any, in a signed image must be verified before loading it. Meanwhile, UEFI specification v2.8b section 32.5.3.3 says, Multiple signatures are allowed to exist in the binary’s certificate table (as per PE/COFF Section “Attribute Certificate Table”). Only one hash or signature is required to be present in db in order to pass validation, so long as neither the SHA-256 hash of the binary nor any present signature is reflected in dbx. This patch makes the semantics of signature verification compliant with the specification mentioned above. Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
746 lines
19 KiB
C
746 lines
19 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Copyright (c) 2018 Patrick Wildt <patrick@blueri.se>
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* Copyright (c) 2019 Linaro Limited, Author: AKASHI Takahiro
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*/
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#include <common.h>
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#include <charset.h>
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#include <efi_loader.h>
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#include <image.h>
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#include <hexdump.h>
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#include <malloc.h>
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#include <crypto/pkcs7.h>
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#include <crypto/pkcs7_parser.h>
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#include <crypto/public_key.h>
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#include <linux/compat.h>
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#include <linux/oid_registry.h>
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#include <u-boot/rsa.h>
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#include <u-boot/sha256.h>
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const efi_guid_t efi_guid_image_security_database =
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EFI_IMAGE_SECURITY_DATABASE_GUID;
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const efi_guid_t efi_guid_sha256 = EFI_CERT_SHA256_GUID;
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const efi_guid_t efi_guid_cert_rsa2048 = EFI_CERT_RSA2048_GUID;
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const efi_guid_t efi_guid_cert_x509 = EFI_CERT_X509_GUID;
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const efi_guid_t efi_guid_cert_x509_sha256 = EFI_CERT_X509_SHA256_GUID;
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const efi_guid_t efi_guid_cert_type_pkcs7 = EFI_CERT_TYPE_PKCS7_GUID;
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#ifdef CONFIG_EFI_SECURE_BOOT
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/**
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* efi_hash_regions - calculate a hash value
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* @regs: Array of regions
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* @count: Number of regions
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* @hash: Pointer to a pointer to buffer holding a hash value
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* @size: Size of buffer to be returned
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*
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* Calculate a sha256 value of @regs and return a value in @hash.
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*
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* Return: true on success, false on error
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*/
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static bool efi_hash_regions(struct image_region *regs, int count,
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void **hash, size_t *size)
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{
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if (!*hash) {
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*hash = calloc(1, SHA256_SUM_LEN);
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if (!*hash) {
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EFI_PRINT("Out of memory\n");
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return false;
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}
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}
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if (size)
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*size = SHA256_SUM_LEN;
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hash_calculate("sha256", regs, count, *hash);
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#ifdef DEBUG
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EFI_PRINT("hash calculated:\n");
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print_hex_dump(" ", DUMP_PREFIX_OFFSET, 16, 1,
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*hash, SHA256_SUM_LEN, false);
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#endif
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return true;
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}
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/**
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* efi_signature_lookup_digest - search for an image's digest in sigdb
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* @regs: List of regions to be authenticated
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* @db: Signature database for trusted certificates
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*
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* A message digest of image pointed to by @regs is calculated and
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* its hash value is compared to entries in signature database pointed
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* to by @db.
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*
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* Return: true if found, false if not
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*/
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bool efi_signature_lookup_digest(struct efi_image_regions *regs,
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struct efi_signature_store *db)
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{
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struct efi_signature_store *siglist;
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struct efi_sig_data *sig_data;
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void *hash = NULL;
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size_t size = 0;
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bool found = false;
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EFI_PRINT("%s: Enter, %p, %p\n", __func__, regs, db);
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if (!regs || !db || !db->sig_data_list)
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goto out;
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for (siglist = db; siglist; siglist = siglist->next) {
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/* TODO: support other hash algorithms */
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if (guidcmp(&siglist->sig_type, &efi_guid_sha256)) {
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EFI_PRINT("Digest algorithm is not supported: %pUl\n",
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&siglist->sig_type);
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break;
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}
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if (!efi_hash_regions(regs->reg, regs->num, &hash, &size)) {
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EFI_PRINT("Digesting an image failed\n");
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break;
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}
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for (sig_data = siglist->sig_data_list; sig_data;
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sig_data = sig_data->next) {
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#ifdef DEBUG
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EFI_PRINT("Msg digest in database:\n");
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print_hex_dump(" ", DUMP_PREFIX_OFFSET, 16, 1,
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sig_data->data, sig_data->size, false);
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#endif
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if (sig_data->size == size &&
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!memcmp(sig_data->data, hash, size)) {
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found = true;
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free(hash);
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goto out;
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}
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}
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free(hash);
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hash = NULL;
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}
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out:
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EFI_PRINT("%s: Exit, found: %d\n", __func__, found);
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return found;
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}
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/**
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* efi_lookup_certificate - find a certificate within db
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* @msg: Signature
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* @db: Signature database
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*
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* Search signature database pointed to by @db and find a certificate
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* pointed to by @cert.
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*
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* Return: true if found, false otherwise.
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*/
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static bool efi_lookup_certificate(struct x509_certificate *cert,
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struct efi_signature_store *db)
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{
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struct efi_signature_store *siglist;
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struct efi_sig_data *sig_data;
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struct image_region reg[1];
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void *hash = NULL, *hash_tmp = NULL;
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size_t size = 0;
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bool found = false;
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EFI_PRINT("%s: Enter, %p, %p\n", __func__, cert, db);
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if (!cert || !db || !db->sig_data_list)
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goto out;
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/*
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* TODO: identify a certificate using sha256 digest
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* Is there any better way?
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*/
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/* calculate hash of TBSCertificate */
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reg[0].data = cert->tbs;
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reg[0].size = cert->tbs_size;
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if (!efi_hash_regions(reg, 1, &hash, &size))
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goto out;
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EFI_PRINT("%s: searching for %s\n", __func__, cert->subject);
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for (siglist = db; siglist; siglist = siglist->next) {
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/* only with x509 certificate */
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if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509))
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continue;
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for (sig_data = siglist->sig_data_list; sig_data;
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sig_data = sig_data->next) {
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struct x509_certificate *cert_tmp;
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cert_tmp = x509_cert_parse(sig_data->data,
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sig_data->size);
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if (IS_ERR_OR_NULL(cert_tmp))
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continue;
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EFI_PRINT("%s: against %s\n", __func__,
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cert_tmp->subject);
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reg[0].data = cert_tmp->tbs;
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reg[0].size = cert_tmp->tbs_size;
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if (!efi_hash_regions(reg, 1, &hash_tmp, NULL))
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goto out;
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x509_free_certificate(cert_tmp);
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if (!memcmp(hash, hash_tmp, size)) {
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found = true;
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goto out;
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}
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}
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}
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out:
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free(hash);
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free(hash_tmp);
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EFI_PRINT("%s: Exit, found: %d\n", __func__, found);
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return found;
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}
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/**
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* efi_verify_certificate - verify certificate's signature with database
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* @signer: Certificate
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* @db: Signature database
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* @root: Certificate to verify @signer
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*
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* Determine if certificate pointed to by @signer may be verified
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* by one of certificates in signature database pointed to by @db.
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*
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* Return: true if certificate is verified, false otherwise.
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*/
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static bool efi_verify_certificate(struct x509_certificate *signer,
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struct efi_signature_store *db,
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struct x509_certificate **root)
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{
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struct efi_signature_store *siglist;
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struct efi_sig_data *sig_data;
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struct x509_certificate *cert;
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bool verified = false;
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int ret;
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EFI_PRINT("%s: Enter, %p, %p\n", __func__, signer, db);
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if (!signer || !db || !db->sig_data_list)
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goto out;
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for (siglist = db; siglist; siglist = siglist->next) {
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/* only with x509 certificate */
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if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509))
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continue;
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for (sig_data = siglist->sig_data_list; sig_data;
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sig_data = sig_data->next) {
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cert = x509_cert_parse(sig_data->data, sig_data->size);
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if (IS_ERR_OR_NULL(cert)) {
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EFI_PRINT("Cannot parse x509 certificate\n");
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continue;
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}
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ret = public_key_verify_signature(cert->pub,
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signer->sig);
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if (!ret) {
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verified = true;
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if (root)
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*root = cert;
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else
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x509_free_certificate(cert);
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goto out;
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}
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x509_free_certificate(cert);
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}
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}
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out:
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EFI_PRINT("%s: Exit, verified: %d\n", __func__, verified);
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return verified;
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}
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/**
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* efi_signature_check_revocation - check revocation with dbx
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* @sinfo: Signer's info
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* @cert: x509 certificate
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* @dbx: Revocation signature database
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*
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* Search revocation signature database pointed to by @dbx and find
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* an entry matching to certificate pointed to by @cert.
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*
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* While this entry contains revocation time, we don't support timestamp
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* protocol at this time and any image will be unconditionally revoked
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* when this match occurs.
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*
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* Return: true if check passed (not found), false otherwise.
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*/
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static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
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struct x509_certificate *cert,
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struct efi_signature_store *dbx)
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{
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struct efi_signature_store *siglist;
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struct efi_sig_data *sig_data;
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struct image_region reg[1];
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void *hash = NULL;
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size_t size = 0;
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time64_t revoc_time;
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bool revoked = false;
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EFI_PRINT("%s: Enter, %p, %p, %p\n", __func__, sinfo, cert, dbx);
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if (!sinfo || !cert || !dbx || !dbx->sig_data_list)
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goto out;
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EFI_PRINT("Checking revocation against %s\n", cert->subject);
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for (siglist = dbx; siglist; siglist = siglist->next) {
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if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509_sha256))
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continue;
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/* calculate hash of TBSCertificate */
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reg[0].data = cert->tbs;
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reg[0].size = cert->tbs_size;
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if (!efi_hash_regions(reg, 1, &hash, &size))
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goto out;
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for (sig_data = siglist->sig_data_list; sig_data;
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sig_data = sig_data->next) {
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/*
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* struct efi_cert_x509_sha256 {
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* u8 tbs_hash[256/8];
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* time64_t revocation_time;
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* };
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*/
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#ifdef DEBUG
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if (sig_data->size >= size) {
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EFI_PRINT("hash in db:\n");
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print_hex_dump(" ", DUMP_PREFIX_OFFSET,
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16, 1,
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sig_data->data, size, false);
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}
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#endif
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if ((sig_data->size < size + sizeof(time64_t)) ||
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memcmp(sig_data->data, hash, size))
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continue;
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memcpy(&revoc_time, sig_data->data + size,
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sizeof(revoc_time));
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EFI_PRINT("revocation time: 0x%llx\n", revoc_time);
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/*
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* TODO: compare signing timestamp in sinfo
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* with revocation time
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*/
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revoked = true;
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free(hash);
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goto out;
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}
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free(hash);
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hash = NULL;
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}
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out:
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EFI_PRINT("%s: Exit, revoked: %d\n", __func__, revoked);
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return !revoked;
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}
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/*
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* efi_signature_verify - verify signatures with db and dbx
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* @regs: List of regions to be authenticated
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* @msg: Signature
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* @db: Signature database for trusted certificates
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* @dbx: Revocation signature database
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*
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* All the signature pointed to by @msg against image pointed to by @regs
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* will be verified by signature database pointed to by @db and @dbx.
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*
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* Return: true if verification for all signatures passed, false otherwise
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*/
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bool efi_signature_verify(struct efi_image_regions *regs,
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struct pkcs7_message *msg,
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struct efi_signature_store *db,
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struct efi_signature_store *dbx)
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{
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struct pkcs7_signed_info *sinfo;
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struct x509_certificate *signer, *root;
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bool verified = false;
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int ret;
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EFI_PRINT("%s: Enter, %p, %p, %p, %p\n", __func__, regs, msg, db, dbx);
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if (!regs || !msg || !db || !db->sig_data_list)
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goto out;
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for (sinfo = msg->signed_infos; sinfo; sinfo = sinfo->next) {
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EFI_PRINT("Signed Info: digest algo: %s, pkey algo: %s\n",
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sinfo->sig->hash_algo, sinfo->sig->pkey_algo);
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/*
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* only for authenticated variable.
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*
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* If this function is called for image,
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* hash calculation will be done in
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* pkcs7_verify_one().
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*/
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if (!msg->data &&
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!efi_hash_regions(regs->reg, regs->num,
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(void **)&sinfo->sig->digest, NULL)) {
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EFI_PRINT("Digesting an image failed\n");
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goto out;
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}
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EFI_PRINT("Verifying certificate chain\n");
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signer = NULL;
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ret = pkcs7_verify_one(msg, sinfo, &signer);
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if (ret == -ENOPKG)
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continue;
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if (ret < 0 || !signer)
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goto out;
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if (sinfo->blacklisted)
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goto out;
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EFI_PRINT("Verifying last certificate in chain\n");
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if (signer->self_signed) {
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if (efi_lookup_certificate(signer, db))
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if (efi_signature_check_revocation(sinfo,
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signer, dbx))
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break;
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} else if (efi_verify_certificate(signer, db, &root)) {
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bool check;
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check = efi_signature_check_revocation(sinfo, root,
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dbx);
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x509_free_certificate(root);
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if (check)
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break;
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}
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EFI_PRINT("Certificate chain didn't reach trusted CA\n");
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}
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if (sinfo)
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verified = true;
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out:
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EFI_PRINT("%s: Exit, verified: %d\n", __func__, verified);
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return verified;
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}
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|
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/**
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* efi_signature_check_signers - check revocation against all signers with dbx
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* @msg: Signature
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* @dbx: Revocation signature database
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*
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* Determine if none of signers' certificates in @msg are revoked
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* by signature database pointed to by @dbx.
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*
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* Return: true if all signers passed, false otherwise.
|
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*/
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bool efi_signature_check_signers(struct pkcs7_message *msg,
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struct efi_signature_store *dbx)
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{
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struct pkcs7_signed_info *sinfo;
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bool revoked = false;
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EFI_PRINT("%s: Enter, %p, %p\n", __func__, msg, dbx);
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|
|
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if (!msg || !dbx)
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goto out;
|
|
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for (sinfo = msg->signed_infos; sinfo; sinfo = sinfo->next) {
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if (sinfo->signer &&
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!efi_signature_check_revocation(sinfo, sinfo->signer,
|
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dbx)) {
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revoked = true;
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break;
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}
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}
|
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out:
|
|
EFI_PRINT("%s: Exit, revoked: %d\n", __func__, revoked);
|
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return !revoked;
|
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}
|
|
|
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/**
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* efi_image_region_add() - add an entry of region
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* @regs: Pointer to array of regions
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* @start: Start address of region (included)
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|
* @end: End address of region (excluded)
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* @nocheck: flag against overlapped regions
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|
*
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* Take one entry of region [@start, @end[ and insert it into the list.
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|
*
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* * If @nocheck is false, the list will be sorted ascending by address.
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|
* Overlapping entries will not be allowed.
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|
*
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|
* * If @nocheck is true, the list will be sorted ascending by sequence
|
|
* of adding the entries. Overlapping is allowed.
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*
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* Return: status code
|
|
*/
|
|
efi_status_t efi_image_region_add(struct efi_image_regions *regs,
|
|
const void *start, const void *end,
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|
int nocheck)
|
|
{
|
|
struct image_region *reg;
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|
int i, j;
|
|
|
|
if (regs->num >= regs->max) {
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|
EFI_PRINT("%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++) {
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|
reg = ®s->reg[i];
|
|
if (nocheck)
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|
continue;
|
|
|
|
/* new data after registered region */
|
|
if (start >= reg->data + reg->size)
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|
continue;
|
|
|
|
/* new data preceding registered region */
|
|
if (end <= reg->data) {
|
|
for (j = regs->num - 1; j >= i; j--)
|
|
memcpy(®s->reg[j + 1], ®s->reg[j],
|
|
sizeof(*reg));
|
|
break;
|
|
}
|
|
|
|
/* new data overlapping registered region */
|
|
EFI_PRINT("%s: new region already part of another\n", __func__);
|
|
return EFI_INVALID_PARAMETER;
|
|
}
|
|
|
|
reg = ®s->reg[i];
|
|
reg->data = start;
|
|
reg->size = end - start;
|
|
regs->num++;
|
|
|
|
return EFI_SUCCESS;
|
|
}
|
|
|
|
/**
|
|
* efi_sigstore_free - free signature store
|
|
* @sigstore: Pointer to signature store structure
|
|
*
|
|
* Feee all the memories held in signature store and itself,
|
|
* which were allocated by efi_sigstore_parse_sigdb().
|
|
*/
|
|
void efi_sigstore_free(struct efi_signature_store *sigstore)
|
|
{
|
|
struct efi_signature_store *sigstore_next;
|
|
struct efi_sig_data *sig_data, *sig_data_next;
|
|
|
|
while (sigstore) {
|
|
sigstore_next = sigstore->next;
|
|
|
|
sig_data = sigstore->sig_data_list;
|
|
while (sig_data) {
|
|
sig_data_next = sig_data->next;
|
|
free(sig_data->data);
|
|
free(sig_data);
|
|
sig_data = sig_data_next;
|
|
}
|
|
|
|
free(sigstore);
|
|
sigstore = sigstore_next;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* efi_sigstore_parse_siglist - parse a signature list
|
|
* @name: Pointer to signature list
|
|
*
|
|
* Parse signature list and instantiate a signature store structure.
|
|
* Signature database is a simple concatenation of one or more
|
|
* signature list(s).
|
|
*
|
|
* Return: Pointer to signature store on success, NULL on error
|
|
*/
|
|
static struct efi_signature_store *
|
|
efi_sigstore_parse_siglist(struct efi_signature_list *esl)
|
|
{
|
|
struct efi_signature_store *siglist = NULL;
|
|
struct efi_sig_data *sig_data, *sig_data_next;
|
|
struct efi_signature_data *esd;
|
|
size_t left;
|
|
|
|
/*
|
|
* UEFI specification defines certificate types:
|
|
* for non-signed images,
|
|
* EFI_CERT_SHA256_GUID
|
|
* EFI_CERT_RSA2048_GUID
|
|
* EFI_CERT_RSA2048_SHA256_GUID
|
|
* EFI_CERT_SHA1_GUID
|
|
* EFI_CERT_RSA2048_SHA_GUID
|
|
* EFI_CERT_SHA224_GUID
|
|
* EFI_CERT_SHA384_GUID
|
|
* EFI_CERT_SHA512_GUID
|
|
*
|
|
* for signed images,
|
|
* EFI_CERT_X509_GUID
|
|
* NOTE: Each certificate will normally be in a separate
|
|
* EFI_SIGNATURE_LIST as the size may vary depending on
|
|
* its algo's.
|
|
*
|
|
* for timestamp revocation of certificate,
|
|
* EFI_CERT_X509_SHA512_GUID
|
|
* EFI_CERT_X509_SHA256_GUID
|
|
* EFI_CERT_X509_SHA384_GUID
|
|
*/
|
|
|
|
if (esl->signature_list_size
|
|
<= (sizeof(*esl) + esl->signature_header_size)) {
|
|
EFI_PRINT("Siglist in wrong format\n");
|
|
return NULL;
|
|
}
|
|
|
|
/* Create a head */
|
|
siglist = calloc(sizeof(*siglist), 1);
|
|
if (!siglist) {
|
|
EFI_PRINT("Out of memory\n");
|
|
goto err;
|
|
}
|
|
memcpy(&siglist->sig_type, &esl->signature_type, sizeof(efi_guid_t));
|
|
|
|
/* Go through the list */
|
|
sig_data_next = NULL;
|
|
left = esl->signature_list_size
|
|
- (sizeof(*esl) + esl->signature_header_size);
|
|
esd = (struct efi_signature_data *)
|
|
((u8 *)esl + sizeof(*esl) + esl->signature_header_size);
|
|
|
|
while (left > 0) {
|
|
/* Signature must exist if there is remaining data. */
|
|
if (left < esl->signature_size) {
|
|
EFI_PRINT("Certificate is too small\n");
|
|
goto err;
|
|
}
|
|
|
|
sig_data = calloc(esl->signature_size
|
|
- sizeof(esd->signature_owner), 1);
|
|
if (!sig_data) {
|
|
EFI_PRINT("Out of memory\n");
|
|
goto err;
|
|
}
|
|
|
|
/* Append signature data */
|
|
memcpy(&sig_data->owner, &esd->signature_owner,
|
|
sizeof(efi_guid_t));
|
|
sig_data->size = esl->signature_size
|
|
- sizeof(esd->signature_owner);
|
|
sig_data->data = malloc(sig_data->size);
|
|
if (!sig_data->data) {
|
|
EFI_PRINT("Out of memory\n");
|
|
goto err;
|
|
}
|
|
memcpy(sig_data->data, esd->signature_data, sig_data->size);
|
|
|
|
sig_data->next = sig_data_next;
|
|
sig_data_next = sig_data;
|
|
|
|
/* Next */
|
|
esd = (struct efi_signature_data *)
|
|
((u8 *)esd + esl->signature_size);
|
|
left -= esl->signature_size;
|
|
}
|
|
siglist->sig_data_list = sig_data_next;
|
|
|
|
return siglist;
|
|
|
|
err:
|
|
efi_sigstore_free(siglist);
|
|
|
|
return NULL;
|
|
}
|
|
|
|
/**
|
|
* efi_sigstore_parse_sigdb - parse a signature database variable
|
|
* @name: Variable's name
|
|
*
|
|
* Read in a value of signature database variable pointed to by
|
|
* @name, parse it and instantiate a signature store structure.
|
|
*
|
|
* Return: Pointer to signature store on success, NULL on error
|
|
*/
|
|
struct efi_signature_store *efi_sigstore_parse_sigdb(u16 *name)
|
|
{
|
|
struct efi_signature_store *sigstore = NULL, *siglist;
|
|
struct efi_signature_list *esl;
|
|
const efi_guid_t *vendor;
|
|
void *db;
|
|
efi_uintn_t db_size;
|
|
efi_status_t ret;
|
|
|
|
if (!u16_strcmp(name, L"PK") || !u16_strcmp(name, L"KEK")) {
|
|
vendor = &efi_global_variable_guid;
|
|
} else if (!u16_strcmp(name, L"db") || !u16_strcmp(name, L"dbx")) {
|
|
vendor = &efi_guid_image_security_database;
|
|
} else {
|
|
EFI_PRINT("unknown signature database, %ls\n", name);
|
|
return NULL;
|
|
}
|
|
|
|
/* retrieve variable data */
|
|
db_size = 0;
|
|
ret = EFI_CALL(efi_get_variable(name, vendor, NULL, &db_size, NULL));
|
|
if (ret == EFI_NOT_FOUND) {
|
|
EFI_PRINT("variable, %ls, not found\n", name);
|
|
sigstore = calloc(sizeof(*sigstore), 1);
|
|
return sigstore;
|
|
} else if (ret != EFI_BUFFER_TOO_SMALL) {
|
|
EFI_PRINT("Getting variable, %ls, failed\n", name);
|
|
return NULL;
|
|
}
|
|
|
|
db = malloc(db_size);
|
|
if (!db) {
|
|
EFI_PRINT("Out of memory\n");
|
|
return NULL;
|
|
}
|
|
|
|
ret = EFI_CALL(efi_get_variable(name, vendor, NULL, &db_size, db));
|
|
if (ret != EFI_SUCCESS) {
|
|
EFI_PRINT("Getting variable, %ls, failed\n", name);
|
|
goto err;
|
|
}
|
|
|
|
/* Parse siglist list */
|
|
esl = db;
|
|
while (db_size > 0) {
|
|
/* List must exist if there is remaining data. */
|
|
if (db_size < sizeof(*esl)) {
|
|
EFI_PRINT("variable, %ls, in wrong format\n", name);
|
|
goto err;
|
|
}
|
|
|
|
if (db_size < esl->signature_list_size) {
|
|
EFI_PRINT("variable, %ls, in wrong format\n", name);
|
|
goto err;
|
|
}
|
|
|
|
/* Parse a single siglist. */
|
|
siglist = efi_sigstore_parse_siglist(esl);
|
|
if (!siglist) {
|
|
EFI_PRINT("Parsing signature list of %ls failed\n",
|
|
name);
|
|
goto err;
|
|
}
|
|
|
|
/* Append siglist */
|
|
siglist->next = sigstore;
|
|
sigstore = siglist;
|
|
|
|
/* Next */
|
|
db_size -= esl->signature_list_size;
|
|
esl = (void *)esl + esl->signature_list_size;
|
|
}
|
|
free(db);
|
|
|
|
return sigstore;
|
|
|
|
err:
|
|
efi_sigstore_free(sigstore);
|
|
free(db);
|
|
|
|
return NULL;
|
|
}
|
|
#endif /* CONFIG_EFI_SECURE_BOOT */
|