[RFC PATCH security-next 2/4] hornet: Introduce sign-ebpf

Blaise Boscaccy
2025-03-21T16:46:18Z

This introduces the sign-ebpf tool. It is very similar to the existing
sign-file script, with one key difference, it will sign a file with
with a signature computed off of arbitrary input data. This can used
to sign an ebpf light skeleton loader program for verification via
hornet.

Typical usage is to provide a payload containing the lskel ebpf
syscall program binary and it's associated maps, which can be
extracted from the auto-generated skel header.

Signed-off-by: Blaise Boscaccy <bboscaccy@linux.microsoft.com>
---
scripts/Makefile | 1 +
scripts/hornet/Makefile | 5 +
scripts/hornet/sign-ebpf.c | 420 +++++++++++++++++++++++++++++++++++++
3 files changed, 426 insertions(+)
create mode 100644 scripts/hornet/Makefile
create mode 100644 scripts/hornet/sign-ebpf.c

diff --git a/scripts/Makefile b/scripts/Makefile
index 46f860529df5e..a2cace05d7342 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -57,6 +57,7 @@ subdir-$(CONFIG_GENKSYMS) += genksyms
subdir-$(CONFIG_GENDWARFKSYMS) += gendwarfksyms
subdir-$(CONFIG_SECURITY_SELINUX) += selinux
subdir-$(CONFIG_SECURITY_IPE) += ipe
+subdir-$(CONFIG_SECURITY_HORNET) += hornet

# Let clean descend into subdirs
subdir- += basic dtc gdb kconfig mod
diff --git a/scripts/hornet/Makefile b/scripts/hornet/Makefile
new file mode 100644
index 0000000000000..ab71dbb8688e4
--- /dev/null
+++ b/scripts/hornet/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+hostprogs-always-y := sign-ebpf
+
+HOSTCFLAGS_sign-ebpf.o = $(shell $(HOSTPKG_CONFIG) --cflags libcrypto 2> /dev/null)
+HOSTLDLIBS_sign-ebpf = $(shell $(HOSTPKG_CONFIG) --libs libcrypto 2> /dev/null || echo -lcrypto)
diff --git a/scripts/hornet/sign-ebpf.c b/scripts/hornet/sign-ebpf.c
new file mode 100644
index 0000000000000..ff98fddb79a15
--- /dev/null
+++ b/scripts/hornet/sign-ebpf.c
@@ -0,0 +1,420 @@
+/* Sign ebpf programs and skeletons using the given key.
+ *
+ * This program is heavily based on the kernel's sign-file tool
+ * with some minor additions to support the signing of eBPF lskels.
+ *
+ * Copyright © 2014-2016 Red Hat, Inc. All Rights Reserved.
+ * Copyright © 2015 Intel Corporation.
+ * Copyright © 2016 Hewlett Packard Enterprise Development LP
+ * Copyright © 2025 Microsoft Corporation.
+ *
+ * Authors: David Howells <dhowells@redhat.com>
+ * David Woodhouse <dwmw2@infradead.org>
+ * Juerg Haefliger <juerg.haefliger@hpe.com>
+ * Blaise Boscaccy <bboscaccy@linux.microsoft.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1
+ * 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/opensslv.h>
+#include <openssl/bio.h>
+#include <openssl/evp.h>
+#include <openssl/pem.h>
+#include <openssl/err.h>
+#if OPENSSL_VERSION_MAJOR >= 3
+# define USE_PKCS11_PROVIDER
+# include <openssl/provider.h>
+# include <openssl/store.h>
+#else
+# if !defined(OPENSSL_NO_ENGINE) && !defined(OPENSSL_NO_DEPRECATED_3_0)
+# define USE_PKCS11_ENGINE
+# include <openssl/engine.h>
+# endif
+#endif
+#include "../ssl-common.h"
+
+/*
+ * Use CMS if we have openssl-1.0.0 or newer available - otherwise we have to
+ * assume that it's not available and its header file is missing and that we
+ * should use PKCS#7 instead. Switching to the older PKCS#7 format restricts
+ * the options we have on specifying the X.509 certificate we want.
+ *
+ * Further, older versions of OpenSSL don't support manually adding signers to
+ * the PKCS#7 message so have to accept that we get a certificate included in
+ * the signature message. Nor do such older versions of OpenSSL support
+ * signing with anything other than SHA1 - so we're stuck with that if such is
+ * the case.
+ */
+#if defined(LIBRESSL_VERSION_NUMBER) || \
+ OPENSSL_VERSION_NUMBER < 0x10000000L || \
+ defined(OPENSSL_NO_CMS)
+#define USE_PKCS7
+#endif
+#ifndef USE_PKCS7
+#include <openssl/cms.h>
+#else
+#include <openssl/pkcs7.h>
+#endif
+
+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[] = "~eBPF signature appended~\n";
+
+static __attribute__((noreturn))
+void format(void)
+{
+ fprintf(stderr,
+ "Usage: scripts/sign-ebpf [-dp] <hash algo> <key> <x509> <bin> <loader> [<dest>]\n");
+ exit(2);
+}
+
+static const char *key_pass;
+
+static int pem_pw_cb(char *buf, int len, int w, void *v)
+{
+ int pwlen;
+
+ if (!key_pass)
+ return -1;
+
+ pwlen = strlen(key_pass);
+ if (pwlen >= len)
+ return -1;
+
+ strcpy(buf, key_pass);
+
+ /* If it's wrong, don't keep trying it. */
+ key_pass = NULL;
+
+ return pwlen;
+}
+
+static EVP_PKEY *read_private_key_pkcs11(const char *private_key_name)
+{
+ EVP_PKEY *private_key = NULL;
+#ifdef USE_PKCS11_PROVIDER
+ OSSL_STORE_CTX *store;
+
+ if (!OSSL_PROVIDER_try_load(NULL, "pkcs11", true))
+ ERR(1, "OSSL_PROVIDER_try_load(pkcs11)");
+ if (!OSSL_PROVIDER_try_load(NULL, "default", true))
+ ERR(1, "OSSL_PROVIDER_try_load(default)");
+
+ store = OSSL_STORE_open(private_key_name, NULL, NULL, NULL, NULL);
+ ERR(!store, "OSSL_STORE_open");
+
+ while (!OSSL_STORE_eof(store)) {
+ OSSL_STORE_INFO *info = OSSL_STORE_load(store);
+
+ if (!info) {
+ drain_openssl_errors(__LINE__, 0);
+ continue;
+ }
+ if (OSSL_STORE_INFO_get_type(info) == OSSL_STORE_INFO_PKEY) {
+ private_key = OSSL_STORE_INFO_get1_PKEY(info);
+ ERR(!private_key, "OSSL_STORE_INFO_get1_PKEY");
+ }
+ OSSL_STORE_INFO_free(info);
+ if (private_key)
+ break;
+ }
+ OSSL_STORE_close(store);
+#elif defined(USE_PKCS11_ENGINE)
+ ENGINE *e;
+
+ ENGINE_load_builtin_engines();
+ drain_openssl_errors(__LINE__, 1);
+ e = ENGINE_by_id("pkcs11");
+ ERR(!e, "Load PKCS#11 ENGINE");
+ if (ENGINE_init(e))
+ drain_openssl_errors(__LINE__, 1);
+ else
+ ERR(1, "ENGINE_init");
+ if (key_pass)
+ ERR(!ENGINE_ctrl_cmd_string(e, "PIN", key_pass, 0), "Set PKCS#11 PIN");
+ private_key = ENGINE_load_private_key(e, private_key_name, NULL, NULL);
+ ERR(!private_key, "%s", private_key_name);
+#else
+ fprintf(stderr, "no pkcs11 engine/provider available\n");
+ exit(1);
+#endif
+ return private_key;
+}
+
+static EVP_PKEY *read_private_key(const char *private_key_name)
+{
+ if (!strncmp(private_key_name, "pkcs11:", 7)) {
+ return read_private_key_pkcs11(private_key_name);
+ } else {
+ EVP_PKEY *private_key;
+ BIO *b;
+
+ b = BIO_new_file(private_key_name, "rb");
+ ERR(!b, "%s", private_key_name);
+ private_key = PEM_read_bio_PrivateKey(b, NULL, pem_pw_cb,
+ NULL);
+ ERR(!private_key, "%s", private_key_name);
+ BIO_free(b);
+
+ return private_key;
+ }
+}
+
+static X509 *read_x509(const char *x509_name)
+{
+ unsigned char buf[2];
+ X509 *x509;
+ BIO *b;
+ int n;
+
+ b = BIO_new_file(x509_name, "rb");
+ ERR(!b, "%s", x509_name);
+
+ /* Look at the first two bytes of the file to determine the encoding */
+ n = BIO_read(b, buf, 2);
+ if (n != 2) {
+ if (BIO_should_retry(b)) {
+ fprintf(stderr, "%s: Read wanted retry\n", x509_name);
+ exit(1);
+ }
+ if (n >= 0) {
+ fprintf(stderr, "%s: Short read\n", x509_name);
+ exit(1);
+ }
+ ERR(1, "%s", x509_name);
+ }
+
+ ERR(BIO_reset(b) != 0, "%s", x509_name);
+
+ if (buf[0] == 0x30 && buf[1] >= 0x81 && buf[1] <= 0x84)
+ /* Assume raw DER encoded X.509 */
+ x509 = d2i_X509_bio(b, NULL);
+ else
+ /* Assume PEM encoded X.509 */
+ x509 = PEM_read_bio_X509(b, NULL, NULL, NULL);
+
+ BIO_free(b);
+ ERR(!x509, "%s", x509_name);
+
+ return x509;
+}
+
+int main(int argc, char **argv)
+{
+ struct module_signature sig_info = { .id_type = PKEY_ID_PKCS7 };
+ char *hash_algo = NULL;
+ char *private_key_name = NULL, *raw_sig_name = NULL;
+ char *x509_name, *bin_name, *loader_name, *dest_name;
+ bool save_sig = false, replace_orig;
+ bool sign_only = false;
+ bool raw_sig = false;
+ unsigned char buf[4096];
+ unsigned long loader_size, sig_size;
+ unsigned int use_signed_attrs;
+ const EVP_MD *digest_algo;
+ EVP_PKEY *private_key;
+#ifndef USE_PKCS7
+ CMS_ContentInfo *cms = NULL;
+ unsigned int use_keyid = 0;
+#else
+ PKCS7 *pkcs7 = NULL;
+#endif
+ X509 *x509;
+ BIO *bd, *bm, *bl;
+ int opt, n;
+ OpenSSL_add_all_algorithms();
+ ERR_load_crypto_strings();
+ ERR_clear_error();
+
+ key_pass = getenv("KBUILD_SIGN_PIN");
+
+#ifndef USE_PKCS7
+ use_signed_attrs = CMS_NOATTR;
+#else
+ use_signed_attrs = PKCS7_NOATTR;
+#endif
+
+ do {
+ opt = getopt(argc, argv, "sdpk");
+ switch (opt) {
+ case 's': raw_sig = true; break;
+ case 'p': save_sig = true; break;
+ case 'd': sign_only = true; save_sig = true; break;
+#ifndef USE_PKCS7
+ case 'k': use_keyid = CMS_USE_KEYID; break;
+#endif
+ case -1: break;
+ default: format();
+ }
+ } while (opt != -1);
+
+ argc -= optind;
+ argv += optind;
+ if (argc < 5 || argc > 6)
+ format();
+
+ if (raw_sig) {
+ raw_sig_name = argv[0];
+ hash_algo = argv[1];
+ } else {
+ hash_algo = argv[0];
+ private_key_name = argv[1];
+ }
+ x509_name = argv[2];
+ bin_name = argv[3];
+ loader_name = argv[4];
+ if (argc == 6 && strcmp(argv[4], argv[5]) != 0) {
+ dest_name = argv[5];
+ replace_orig = false;
+ } else {
+ ERR(asprintf(&dest_name, "%s.~signed~", loader_name) < 0,
+ "asprintf");
+ replace_orig = true;
+ }
+
+#ifdef USE_PKCS7
+ if (strcmp(hash_algo, "sha1") != 0) {
+ fprintf(stderr, "sign-file: %s only supports SHA1 signing\n",
+ OPENSSL_VERSION_TEXT);
+ exit(3);
+ }
+#endif
+
+ /* Open the bin file */
+ bm = BIO_new_file(bin_name, "rb");
+ ERR(!bm, "%s", bin_name);
+
+ if (!raw_sig) {
+ /* Read the private key and the X.509 cert the PKCS#7 message
+ * will point to.
+ */
+ private_key = read_private_key(private_key_name);
+ x509 = read_x509(x509_name);
+
+ /* Digest the module data. */
+ OpenSSL_add_all_digests();
+ drain_openssl_errors(__LINE__, 0);
+ digest_algo = EVP_get_digestbyname(hash_algo);
+ ERR(!digest_algo, "EVP_get_digestbyname");
+
+#ifndef USE_PKCS7
+ /* Load the signature message from the digest buffer. */
+ cms = CMS_sign(NULL, NULL, NULL, NULL,
+ CMS_NOCERTS | CMS_PARTIAL | CMS_BINARY |
+ CMS_DETACHED | CMS_STREAM);
+ ERR(!cms, "CMS_sign");
+
+ ERR(!CMS_add1_signer(cms, x509, private_key, digest_algo,
+ CMS_NOCERTS | CMS_BINARY |
+ CMS_NOSMIMECAP | use_keyid |
+ use_signed_attrs),
+ "CMS_add1_signer");
+ ERR(CMS_final(cms, bm, NULL, CMS_NOCERTS | CMS_BINARY) != 1,
+ "CMS_final");
+
+#else
+ pkcs7 = PKCS7_sign(x509, private_key, NULL, bm,
+ PKCS7_NOCERTS | PKCS7_BINARY |
+ PKCS7_DETACHED | use_signed_attrs);
+ ERR(!pkcs7, "PKCS7_sign");
+#endif
+
+ if (save_sig) {
+ char *sig_file_name;
+ BIO *b;
+
+ ERR(asprintf(&sig_file_name, "%s.p7s", bin_name) < 0,
+ "asprintf");
+ b = BIO_new_file(sig_file_name, "wb");
+ ERR(!b, "%s", sig_file_name);
+#ifndef USE_PKCS7
+ ERR(i2d_CMS_bio_stream(b, cms, NULL, 0) != 1,
+ "%s", sig_file_name);
+#else
+ ERR(i2d_PKCS7_bio(b, pkcs7) != 1,
+ "%s", sig_file_name);
+#endif
+ BIO_free(b);
+ }
+
+ if (sign_only) {
+ BIO_free(bm);
+ return 0;
+ }
+ }
+
+ /* Open the destination file now so that we can shovel the loader data
+ * across as we read it.
+ */
+ bd = BIO_new_file(dest_name, "wb");
+ ERR(!bd, "%s", dest_name);
+
+ bl = BIO_new_file(loader_name, "rb");
+ ERR(!bl, "%s", loader_name);
+
+
+ /* Append the marker and the PKCS#7 message to the destination file */
+ ERR(BIO_reset(bm) < 0, "%s", bin_name);
+ ERR(BIO_reset(bl) < 0, "%s", loader_name);
+ while ((n = BIO_read(bl, buf, sizeof(buf))),
+ n > 0) {
+ ERR(BIO_write(bd, buf, n) < 0, "%s", dest_name);
+ }
+ BIO_free(bl);
+ BIO_free(bm);
+ ERR(n < 0, "%s", loader_name);
+ loader_size = BIO_number_written(bd);
+
+ if (!raw_sig) {
+#ifndef USE_PKCS7
+ ERR(i2d_CMS_bio_stream(bd, cms, NULL, 0) != 1, "%s", dest_name);
+#else
+ ERR(i2d_PKCS7_bio(bd, pkcs7) != 1, "%s", dest_name);
+#endif
+ } else {
+ BIO *b;
+
+ /* Read the raw signature file and write the data to the
+ * destination file
+ */
+ b = BIO_new_file(raw_sig_name, "rb");
+ ERR(!b, "%s", raw_sig_name);
+ while ((n = BIO_read(b, buf, sizeof(buf))), n > 0)
+ ERR(BIO_write(bd, buf, n) < 0, "%s", dest_name);
+ BIO_free(b);
+ }
+
+ sig_size = BIO_number_written(bd) - loader_size;
+ sig_info.sig_len = htonl(sig_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) != 1, "%s", dest_name);
+
+ /* Finally, if we're signing in place, replace the original. */
+ if (replace_orig)
+ ERR(rename(dest_name, loader_name) < 0, "%s", dest_name);
+
+ return 0;
+}
--
2.48.1