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    Subject[PATCH 4/8] MODSIGN: Provide a utility to append a PKCS#7 signature to a module [ver #4]
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    Date
    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>
    ---

    include/crypto/public_key.h | 1
    scripts/sign-file.c | 205 +++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 206 insertions(+)
    create mode 100755 scripts/sign-file.c

    diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
    index b6f27a240856..fda097e079a4 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..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;
    +}


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