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Date: Fri, 03 Oct 2014 15:30:31 +0100
From: David Howells <dhowells@...hat.com>
To: rusty@...tcorp.com.au
Cc: dhowells@...hat.com, linux-security-module@...r.kernel.org,
keyrings@...ux-nfs.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] MODSIGN: Provide a utility to append a PKCS#7 signature
to a module
Provide a utility that:
(1) Digests a module using the specified hash algorithm (typically sha256).
[The digest can be dumped into a file by passing the '-d' flag]
(2) Generates a PKCS#7 message that:
(a) Has detached data (ie. the module content).
(b) Is signed with the specified private key.
(c) Refers to the specified X.509 certificate.
(d) Has an empty X.509 certificate list.
[The PKCS#7 message can be dumped into a file by passing the '-p' flag]
(3) Generates a signed module by concatenating the old module, the PKCS#7
message, a descriptor and a magic string. The descriptor contains the
size of the PKCS#7 message and indicates the id_type as PKEY_ID_PKCS7.
(4) Either writes the signed module to the specified destination or renames
it over the source module.
This allows module signing to reuse the PKCS#7 handling code that was added
for PE file parsing for signed kexec.
Note that the utility is written in C and must be linked against the OpenSSL
crypto library.
Note further that I have temporarily dropped support for handling externally
created signatures until we can work out the best way to do those. Hopefully,
whoever creates the signature can give me a PKCS#7 certificate.
Signed-off-by: David Howells <dhowells@...hat.com>
---
include/crypto/public_key.h | 1
scripts/sign-file.c | 189 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 190 insertions(+)
create mode 100755 scripts/sign-file.c
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index fa73a6fd536c..a2da37710621 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -33,6 +33,7 @@ extern const struct public_key_algorithm *pkey_algo[PKEY_ALGO__LAST];
enum pkey_id_type {
PKEY_ID_PGP, /* OpenPGP generated key ID */
PKEY_ID_X509, /* X.509 arbitrary subjectKeyIdentifier */
+ PKEY_ID_PKCS7, /* Signature in PKCS#7 message */
PKEY_ID_TYPE__LAST
};
diff --git a/scripts/sign-file.c b/scripts/sign-file.c
new file mode 100755
index 000000000000..3f9bedbd185f
--- /dev/null
+++ b/scripts/sign-file.c
@@ -0,0 +1,189 @@
+/* Sign a module file using the given key.
+ *
+ * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@...hat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <getopt.h>
+#include <err.h>
+#include <arpa/inet.h>
+#include <openssl/bio.h>
+#include <openssl/evp.h>
+#include <openssl/pem.h>
+#include <openssl/pkcs7.h>
+#include <openssl/err.h>
+
+struct module_signature {
+ uint8_t algo; /* Public-key crypto algorithm [0] */
+ uint8_t hash; /* Digest algorithm [0] */
+ uint8_t id_type; /* Key identifier type [PKEY_ID_PKCS7] */
+ uint8_t signer_len; /* Length of signer's name [0] */
+ uint8_t key_id_len; /* Length of key identifier [0] */
+ uint8_t __pad[3];
+ uint32_t sig_len; /* Length of signature data */
+};
+
+#define PKEY_ID_PKCS7 2
+
+static char magic_number[] = "~Module signature appended~\n";
+
+static __attribute__((noreturn))
+void format(void)
+{
+ fprintf(stderr,
+ "Usage: scripts/sign-file [-dp] <hash algo> <key> <x509> <module> [<dest>]\n");
+ exit(2);
+}
+
+static void display_openssl_errors(int l)
+{
+ const char *file;
+ char buf[120];
+ int e, line;
+
+ if (ERR_peek_error() == 0)
+ return;
+ fprintf(stderr, "At main.c:%d:\n", l);
+
+ while ((e = ERR_get_error_line(&file, &line))) {
+ ERR_error_string(e, buf);
+ fprintf(stderr, "- SSL %s: %s:%d\n", buf, file, line);
+ }
+}
+
+
+#define ERR(cond, ...) \
+ do { \
+ bool __cond = (cond); \
+ display_openssl_errors(__LINE__); \
+ if (__cond) { \
+ err(1, ## __VA_ARGS__); \
+ } \
+ } while(0)
+
+int main(int argc, char **argv)
+{
+ struct module_signature sig_info = { .id_type = PKEY_ID_PKCS7 };
+ char *hash_algo = NULL;
+ char *private_key_name, *x509_name, *module_name, *dest_name;
+ bool save_pkcs7 = false, replace_orig;
+ unsigned char buf[4096];
+ unsigned long module_size, pkcs7_size;
+ const EVP_MD *digest_algo;
+ EVP_PKEY *private_key;
+ PKCS7 *pkcs7;
+ X509 *x509;
+ BIO *b, *bd, *bm;
+ int opt, n;
+
+ do {
+ opt = getopt(argc, argv, "dp");
+ switch (opt) {
+ case 'p': save_pkcs7 = true; break;
+ case -1: break;
+ default: format();
+ }
+ } while (opt != -1);
+
+ argc -= optind;
+ argv += optind;
+ if (argc < 4 || argc > 5)
+ format();
+
+ hash_algo = argv[0];
+ private_key_name = argv[1];
+ x509_name = argv[2];
+ module_name = argv[3];
+ if (argc == 5) {
+ dest_name = argv[4];
+ replace_orig = false;
+ } else {
+ ERR(asprintf(&dest_name, "%s.~signed~", module_name) < 0,
+ "asprintf");
+ replace_orig = true;
+ }
+
+ ERR_load_crypto_strings();
+ ERR_clear_error();
+
+ /* Read the private key and the X.509 cert the PKCS#7 message
+ * will point to.
+ */
+ b = BIO_new_file(private_key_name, "rb");
+ ERR(!b, "%s", private_key_name);
+ private_key = PEM_read_bio_PrivateKey(b, NULL, NULL, NULL);
+ BIO_free(b);
+
+ b = BIO_new_file(x509_name, "rb");
+ ERR(!b, "%s", x509_name);
+ x509 = PEM_read_bio_X509(b, NULL, NULL, NULL);
+ BIO_free(b);
+
+ /* Open the destination file now so that we can shovel the module data
+ * across as we read it.
+ */
+ bd = BIO_new_file(dest_name, "wb");
+ ERR(!bd, dest_name);
+
+ /* Digest the module data. */
+ OpenSSL_add_all_digests();
+ display_openssl_errors(__LINE__);
+ digest_algo = EVP_get_digestbyname(hash_algo);
+ ERR(!digest_algo, "EVP_get_digestbyname");
+
+ bm = BIO_new_file(module_name, "rb");
+ ERR(!bm, "%s", module_name);
+
+ /* Load the PKCS#7 message from the digest buffer. */
+ pkcs7 = PKCS7_sign(NULL, NULL, NULL, NULL,
+ PKCS7_NOCERTS | PKCS7_PARTIAL | PKCS7_BINARY | PKCS7_DETACHED | PKCS7_STREAM);
+ ERR(!pkcs7, "PKCS7_sign");
+
+ ERR(PKCS7_sign_add_signer(pkcs7, x509, private_key, digest_algo, PKCS7_NOCERTS | PKCS7_BINARY) < 0,
+ "PKCS7_sign_add_signer");
+ ERR(PKCS7_final(pkcs7, bm, PKCS7_NOCERTS | PKCS7_BINARY) < 0,
+ "PKCS7_final");
+
+ if (save_pkcs7) {
+ char *pkcs7_name;
+
+ ERR(asprintf(&pkcs7_name, "%s.pkcs7", module_name) < 0, "asprintf");
+ b = BIO_new_file(pkcs7_name, "wb");
+ ERR(!b, pkcs7_name);
+ ERR(i2d_PKCS7_bio_stream(b, pkcs7, NULL, 0) < 0, pkcs7_name);
+ BIO_free(b);
+ }
+
+ /* Append the marker and the PKCS#7 message to the destination file */
+ ERR(BIO_reset(bm) < 0, module_name);
+ while ((n = BIO_read(bm, buf, sizeof(buf))),
+ n > 0) {
+ ERR(BIO_write(bd, buf, n) < 0, dest_name);
+ }
+ ERR(n < 0, module_name);
+ module_size = BIO_number_written(bd);
+
+ ERR(i2d_PKCS7_bio_stream(bd, pkcs7, NULL, 0) < 0, dest_name);
+ pkcs7_size = BIO_number_written(bd) - module_size;
+ sig_info.sig_len = htonl(pkcs7_size);
+ ERR(BIO_write(bd, &sig_info, sizeof(sig_info)) < 0, dest_name);
+ ERR(BIO_write(bd, magic_number, sizeof(magic_number) - 1) < 0, dest_name);
+
+ ERR(BIO_free(bd) < 0, dest_name);
+
+ /* Finally, if we're signing in place, replace the original. */
+ if (replace_orig)
+ ERR(rename(dest_name, module_name) < 0, dest_name);
+
+ return 0;
+}
--
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