Re: [PATCH v5 07/10] hornet: Introduce gen_sig

Fan Wu
2026-04-21T00:19:09Z

On Mon, Apr 20, 2026 at 2:27 PM Blaise Boscaccy
<bboscaccy@linux.microsoft.com> wrote:
>
> This introduces the gen_sig tool. It creates a pkcs#7 signature of a
> data payload. Additionally it appends a signed attribute containing a
> set of hashes.
>
> Typical usage is to provide a payload containing the light skeleton
> ebpf syscall program binary and it's associated maps, which can be
> extracted from the auto-generated skeleton header.
>
> Signed-off-by: Blaise Boscaccy <bboscaccy@linux.microsoft.com>
> ---
> scripts/Makefile | 1 +
> scripts/hornet/Makefile | 5 +
> scripts/hornet/gen_sig.c | 392 ++++++++++++++++++++++++++++++++++++
> scripts/hornet/write-sig.sh | 27 +++
> 4 files changed, 425 insertions(+)
> create mode 100644 scripts/hornet/Makefile
> create mode 100644 scripts/hornet/gen_sig.c
> create mode 100755 scripts/hornet/write-sig.sh
>
> diff --git a/scripts/Makefile b/scripts/Makefile
> index 0941e5ce7b575..dea8ab91bbe4e 100644
> --- a/scripts/Makefile
> +++ b/scripts/Makefile
> @@ -63,6 +63,7 @@ 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..3ee41e5e9a9ff
> --- /dev/null
> +++ b/scripts/hornet/Makefile
> @@ -0,0 +1,5 @@
> +# SPDX-License-Identifier: GPL-2.0
> +hostprogs-always-y := gen_sig
> +
> +HOSTCFLAGS_gen_sig.o = $(shell $(HOSTPKG_CONFIG) --cflags libcrypto 2> /dev/null)
> +HOSTLDLIBS_gen_sig = $(shell $(HOSTPKG_CONFIG) --libs libcrypto 2> /dev/null || echo -lcrypto)
> diff --git a/scripts/hornet/gen_sig.c b/scripts/hornet/gen_sig.c
> new file mode 100644
> index 0000000000000..f966516ebc99b
> --- /dev/null
> +++ b/scripts/hornet/gen_sig.c
> @@ -0,0 +1,392 @@
> +/* SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
> + *
> + * Generate a signature for an eBPF program along with appending
> + * map hashes as signed attributes
> + *
> + * Copyright © 2025 Microsoft Corporation.
> + *
> + * Authors: 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 <string.h>
> +#include <stdlib.h>
> +#include <errno.h>
> +#include <stdbool.h>
> +#include <stdint.h>
> +#include <err.h>
> +#include <getopt.h>
> +
> +#include <openssl/cms.h>
> +#include <openssl/err.h>
> +#include <openssl/evp.h>
> +#include <openssl/pkcs7.h>
> +#include <openssl/x509.h>
> +#include <openssl/pem.h>
> +#include <openssl/objects.h>
> +#include <openssl/asn1.h>
> +#include <openssl/asn1t.h>
> +#include <openssl/opensslv.h>
> +#include <openssl/bio.h>
> +#include <openssl/stack.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"
> +
> +#define SHA256_LEN 32
> +#define BUF_SIZE (1 << 15) // 32 KiB
> +#define MAX_HASHES 64
> +
> +struct hash_spec {
> + char *file;
> + int index;
> +};
> +
> +typedef struct {
> + ASN1_INTEGER *index;
> + ASN1_OCTET_STRING *hash;
> +
> +} HORNET_MAP;
> +
> +DECLARE_ASN1_FUNCTIONS(HORNET_MAP)
> +ASN1_SEQUENCE(HORNET_MAP) = {
> + ASN1_SIMPLE(HORNET_MAP, index, ASN1_INTEGER),
> + ASN1_SIMPLE(HORNET_MAP, hash, ASN1_OCTET_STRING)
> +} ASN1_SEQUENCE_END(HORNET_MAP);
> +
> +IMPLEMENT_ASN1_FUNCTIONS(HORNET_MAP)
> +
> +DEFINE_STACK_OF(HORNET_MAP)
> +
> +typedef struct {
> + STACK_OF(HORNET_MAP) * maps;
> +} MAP_SET;
> +
> +DECLARE_ASN1_FUNCTIONS(MAP_SET)
> +ASN1_SEQUENCE(MAP_SET) = {
> + ASN1_SET_OF(MAP_SET, maps, HORNET_MAP)
> +} ASN1_SEQUENCE_END(MAP_SET);
> +
> +IMPLEMENT_ASN1_FUNCTIONS(MAP_SET)
> +
> +#define DIE(...) do { fprintf(stderr, __VA_ARGS__); fputc('\n', stderr); \
> + exit(EXIT_FAILURE); } while (0)
> +
> +static BIO *bio_open_wr(const char *path)
> +{
> + BIO *b = BIO_new_file(path, "wb");
> +
> + if (!b) {
> + perror(path);
> + ERR_print_errors_fp(stderr);
> + exit(EXIT_FAILURE);
> + }
> + return b;
> +}
> +
> +static void usage(const char *prog)
> +{
> + fprintf(stderr,
> + "Usage:\n"
> + " %s --data content.bin --cert signer.crt --key signer.key [-pass pass]\n"
> + " --out newsig.p7b \n"
> + " --add FILE:index [--add FILE:index ...]\n",
> + prog);
> +}
> +
> +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);
> +
> + key_pass = NULL;
> +
> + return pwlen;
> +}
> +
> +static EVP_PKEY *read_private_key(const char *private_key_name)
> +{
> + 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;
> +}
> +
> +static int sha256(const char *path, unsigned char out[SHA256_LEN], unsigned int *out_len)
> +{
> + FILE *f;
> + int rc;
> + EVP_MD_CTX *ctx;
> + unsigned char buf[BUF_SIZE];
> + size_t n;
> + unsigned int mdlen = 0;
> +
> + if (!path || !out)
> + return -1;
> +
> + f = fopen(path, "rb");
> + if (!f) {
> + perror("fopen");
> + return -2;
> + }
> +
> + ERR_load_crypto_strings();
> +
> + rc = -3;
> + ctx = EVP_MD_CTX_new();
> + if (!ctx) {
> + rc = -4;
> + goto done;
> + }
> +
> +#if OPENSSL_VERSION_NUMBER >= 0x30000000L
> + if (EVP_DigestInit_ex2(ctx, EVP_sha256(), NULL) != 1) {
> + rc = -5;
> + goto done;
> + }
> +#else
> + if (EVP_DigestInit_ex(ctx, EVP_sha256(), NULL) != 1) {
> + rc = -5;
> + goto done;
> + }
> +#endif
> + while ((n = fread(buf, 1, sizeof(buf), f)) > 0) {
> + if (EVP_DigestUpdate(ctx, buf, n) != 1) {
> + rc = -6;
> + goto done;
> + }
> + }
> + if (ferror(f)) {
> + rc = -7;
> + goto done;
> + }
> +
> + if (EVP_DigestFinal_ex(ctx, out, &mdlen) != 1) {
> + rc = -8;
> + goto done;
> + }
> + if (mdlen != SHA256_LEN) {
> + rc = -9;
> + goto done;
> + }
> +
> + if (out_len)
> + *out_len = mdlen;
> + rc = 0;
> +
> +done:
> + EVP_MD_CTX_free(ctx);
> + fclose(f);
> + ERR_free_strings();
> + return rc;
> +}
> +
> +static void add_hash(MAP_SET *set, unsigned char *buffer, int buffer_len, int index)
> +{
> + HORNET_MAP *map = NULL;
> +
> + map = HORNET_MAP_new();
> + ASN1_INTEGER_set(map->index, index);
> + ASN1_OCTET_STRING_set(map->hash, buffer, buffer_len);
> + sk_HORNET_MAP_push(set->maps, map);
> +}
> +
> +int main(int argc, char **argv)
> +{
> + const char *cert_path = NULL;
> + const char *key_path = NULL;
> + const char *data_path = NULL;
> + const char *out_path = NULL;
> +
> + X509 *signer;
> + EVP_PKEY *pkey;
> + BIO *data_in;
> + CMS_ContentInfo *cms_out;
> + struct hash_spec hashes[MAX_HASHES];
> + int hash_count = 0;
> + int flags;
> + CMS_SignerInfo *si;
> + MAP_SET *set;
> + unsigned char hash_buffer[SHA256_LEN];
> + unsigned int hash_len;
> + ASN1_OBJECT *oid;
> + unsigned char *der = NULL;
> + int der_len;
> + int err;
> + BIO *b_out;
> + int i;
> + char opt;
> +
> + const char *short_opts = "C:K:P:O:A:Sh";
> +
> + static const struct option long_opts[] = {
> + {"cert", required_argument, 0, 'C'},
> + {"key", required_argument, 0, 'K'},
> + {"pass", required_argument, 0, 'P'},
> + {"out", required_argument, 0, 'O'},
> + {"data", required_argument, 0, 'D'},
> + {"add", required_argument, 0, 'A'},
> + {"help", no_argument, 0, 'h'},
> + {0, 0, 0, 0}
> + };
> +
> + while ((opt = getopt_long_only(argc, argv, short_opts, long_opts, NULL)) != -1) {
> + switch (opt) {
> + case 'C':
> + cert_path = optarg;
> + break;
> + case 'K':
> + key_path = optarg;
> + break;
> + case 'P':
> + key_pass = optarg;
> + break;
> + case 'O':
> + out_path = optarg;
> + break;
> + case 'D':
> + data_path = optarg;
> + break;
> + case 'A':
> + if (strchr(optarg, ':')) {
> + hashes[hash_count].file = strsep(&optarg, ":");
> + hashes[hash_count].index = atoi(optarg);
> + hash_count++;

Should the hash_count be compared to MAX_HASHES here?

> + } else {
> + usage(argv[0]);
> + return EXIT_FAILURE;
> + }
> + }
> + }
> +
> + if (!cert_path || !key_path || !out_path || !data_path) {
> + usage(argv[0]);
> + return EXIT_FAILURE;
> + }
> +
> + OpenSSL_add_all_algorithms();
> + ERR_load_crypto_strings();
> +
> + signer = read_x509(cert_path);
> + ERR(!signer, "Load cert failed");
> +
> + pkey = read_private_key(key_path);
> + ERR(!pkey, "Load key failed");
> +
> + data_in = BIO_new_file(data_path, "rb");
> + ERR(!data_in, "Load data failed");
> +
> + cms_out = CMS_sign(NULL, NULL, NULL, NULL,
> + CMS_NOCERTS | CMS_PARTIAL | CMS_BINARY | CMS_DETACHED);
> + ERR(!cms_out, "create cms failed");
> +
> + flags = CMS_NOCERTS | CMS_PARTIAL | CMS_BINARY | CMS_NOSMIMECAP | CMS_DETACHED;
> +
> + si = CMS_add1_signer(cms_out, signer, pkey, EVP_sha256(), flags);
> + ERR(!si, "add signer failed");
> +
> + set = MAP_SET_new();
> + set->maps = sk_HORNET_MAP_new_null();
> +
> + for (i = 0; i < hash_count; i++) {
> + sha256(hashes[i].file, hash_buffer, &hash_len);

Can sha256 fail here? In that case the program should stop here and
report errors.

-Fan

> + add_hash(set, hash_buffer, hash_len, hashes[i].index);
> + }
> +
> + oid = OBJ_txt2obj("2.25.316487325684022475439036912669789383960", 1);
> + if (!oid) {
> + ERR_print_errors_fp(stderr);
> + DIE("create oid failed");
> + }
> +
> + der_len = ASN1_item_i2d((ASN1_VALUE *)set, &der, ASN1_ITEM_rptr(MAP_SET));
> + CMS_signed_add1_attr_by_OBJ(si, oid, V_ASN1_SEQUENCE, der, der_len);
> +
> + err = CMS_final(cms_out, data_in, NULL, CMS_NOCERTS | CMS_BINARY);
> + ERR(!err, "cms final failed");
> +
> + OPENSSL_free(der);
> + MAP_SET_free(set);
> +
> + b_out = bio_open_wr(out_path);
> + ERR(!b_out, "opening output path failed");
> +
> + i2d_CMS_bio_stream(b_out, cms_out, NULL, 0);
> +
> + BIO_free(data_in);
> + BIO_free(b_out);
> + EVP_cleanup();
> + ERR_free_strings();
> + return 0;
> +}
> diff --git a/scripts/hornet/write-sig.sh b/scripts/hornet/write-sig.sh
> new file mode 100755
> index 0000000000000..7eaabe3bab9aa
> --- /dev/null
> +++ b/scripts/hornet/write-sig.sh
> @@ -0,0 +1,27 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (c) 2025 Microsoft Corporation
> +#
> +# This program is free software; you can redistribute it and/or
> +# modify it under the terms of version 2 of the GNU General Public
> +# License as published by the Free Software Foundation.
> +
> +function usage() {
> + echo "Sample for rewriting an autogenerated eBPF lskel headers"
> + echo "with a new signature"
> + echo ""
> + echo "USAGE: header_file sig"
> + exit
> +}
> +
> +ARGC=$#
> +
> +EXPECTED_ARGS=2
> +
> +if [ $ARGC -ne $EXPECTED_ARGS ] ; then
> + usage
> +else
> + SIG=$(xxd -p $2 | tr -d '\n' | sed 's/\(..\)/\\\\x\1/g')
> + sed '/const char opts_sig/,/;/c\\tstatic const char opts_sig[] __attribute__((__aligned__(8))) = "\\\n'"$(printf '%s\n' "$SIG")"'\";' $1
> +fi
> --
> 2.53.0
>