[PATCH bpf-next v5 5/8] bpftool: Cover loader metadata with the program signature
From: Daniel Borkmann <daniel@iogearbox.net>
Date: 2026-07-07 19:31:11
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [tooling] (bpftool), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Quentin Monnet, Linus Torvalds
bpftool_prog_sign() signed only the loader instructions. The metadata blob the loader installs was left to an in-loader hash check, which the kernel now performs at load time over insns || metadata. Sign that same concatenation: pass the metadata blob (gen_loader_opts data) through to bpftool_prog_sign() and feed insns || metadata to CMS_final(). The excl_prog_hash stays a digest of the instructions alone; it binds the metadata map to the loader and is matched against prog->digest by the verifier, independent of what the signature covers. The signed artifact is now plain data: both bytes the signature covers are embedded verbatim in the generated skeleton, so signing and verifying an lskel is an ordinary CMS operation that a signer or auditor can perform (or reproduce) offline, without analyzing loader bytecode to establish what the signature actually attests to. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> --- tools/bpf/bpftool/gen.c | 2 ++ tools/bpf/bpftool/sign.c | 17 +++++++++++++++-- 2 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 6ae7262ebe0c..a01d06d22d1a 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c@@ -793,6 +793,8 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h if (sign_progs) { sopts.insns = opts.insns; sopts.insns_sz = opts.insns_sz; + sopts.data = opts.data; + sopts.data_sz = opts.data_sz; sopts.excl_prog_hash = prog_sha; sopts.excl_prog_hash_sz = sizeof(prog_sha); sopts.signature = sig_buf;
diff --git a/tools/bpf/bpftool/sign.c b/tools/bpf/bpftool/sign.c
index 1257dba8ef2f..88726a6db6d0 100644
--- a/tools/bpf/bpftool/sign.c
+++ b/tools/bpf/bpftool/sign.c@@ -135,9 +135,21 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts) CMS_ContentInfo *cms = NULL; long actual_sig_len = 0; X509 *x509 = NULL; + void *data = NULL; + size_t data_sz; int err = 0; - bd_in = BIO_new_mem_buf(opts->insns, opts->insns_sz); + data_sz = (size_t)opts->insns_sz + opts->data_sz; + data = malloc(data_sz); + if (!data) { + err = -ENOMEM; + goto cleanup; + } + memcpy(data, opts->insns, opts->insns_sz); + if (opts->data_sz) + memcpy((char *)data + opts->insns_sz, opts->data, opts->data_sz); + + bd_in = BIO_new_mem_buf(data, data_sz); if (!bd_in) { err = -ENOMEM; goto cleanup;
@@ -181,7 +193,7 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts) goto cleanup; } - bd_out = BIO_new(BIO_s_mem()); + bd_out = BIO_new(BIO_s_mem()); if (!bd_out) { err = -ENOMEM; goto cleanup;
@@ -215,6 +227,7 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts) X509_free(x509); EVP_PKEY_free(private_key); BIO_free(bd_in); + free(data); DISPLAY_OSSL_ERR(err < 0); return err; }
--
2.43.0