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@redhat.com>
Tested-by: Vivek Goyal <vgoyal@redhat.com>

diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index b6f27a240856c2efeef6cb199e2ba1543f8b6334..fda097e079a4cc166e0a0d8e5047069564392f5c 100644 (file)
--- 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 (executable)
index 0000000..5b8a6dd
--- /dev/null
+++ b/scripts/sign-file.c
@@ -0,0 +1,205 @@
+/* Sign a module file using the given key.
+ *
+ * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.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);
+       }
+}
+
+static void drain_openssl_errors(void)
+{
+       const char *file;
+       int line;
+
+       if (ERR_peek_error() == 0)
+               return;
+       while (ERR_get_error_line(&file, &line)) {}
+}
+
+#define ERR(cond, fmt, ...)                            \
+       do {                                            \
+               bool __cond = (cond);                   \
+               display_openssl_errors(__LINE__);       \
+               if (__cond) {                           \
+                       err(1, fmt, ## __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;
+
+       ERR_load_crypto_strings();
+       ERR_clear_error();
+
+       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;
+       }
+
+       /* 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 = d2i_X509_bio(b, NULL); /* Binary encoded X.509 */
+       if (!x509) {
+               BIO_reset(b);
+               x509 = PEM_read_bio_X509(b, NULL, NULL, NULL); /* PEM encoded X.509 */
+               if (x509)
+                       drain_openssl_errors();
+       }
+       BIO_free(b);
+       ERR(!x509, "%s", x509_name);
+
+       /* 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, "%s", 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),
+           "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, "%s", pkcs7_name);
+               ERR(i2d_PKCS7_bio_stream(b, pkcs7, NULL, 0) < 0, "%s", pkcs7_name);
+               BIO_free(b);
+       }
+
+       /* Append the marker and the PKCS#7 message to the destination file */
+       ERR(BIO_reset(bm) < 0, "%s", module_name);
+       while ((n = BIO_read(bm, buf, sizeof(buf))),
+              n > 0) {
+               ERR(BIO_write(bd, buf, n) < 0, "%s", dest_name);
+       }
+       ERR(n < 0, "%s", module_name);
+       module_size = BIO_number_written(bd);
+
+       ERR(i2d_PKCS7_bio_stream(bd, pkcs7, NULL, 0) < 0, "%s", 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, "%s", dest_name);
+       ERR(BIO_write(bd, magic_number, sizeof(magic_number) - 1) < 0, "%s", dest_name);
+
+       ERR(BIO_free(bd) < 0, "%s", dest_name);
+
+       /* Finally, if we're signing in place, replace the original. */
+       if (replace_orig)
+               ERR(rename(dest_name, module_name) < 0, "%s", dest_name);
+
+       return 0;
+}