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>

1 files changed, 205 insertions, 0 deletions

diff --git a/scripts/sign-file.c b/scripts/sign-file.c
new file mode 100755
index 000000000000..5b8a6dda3235
--- /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;
+}