Re: [PATCH bpf-next v2 04/11] bpftool: Support ML-DSA program signing

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Dropping `CMS_NOATTR` for ML-DSA without adding `CMS_NO_SIGNING_TIME` causes non-deterministic signatures, breaking reproducible builds for BPF skeletons.
--

--- Patch [4]: [PATCH bpf-next v2 04/11] bpftool: Support ML-DSA program signing ---
commit 1bfca914da9c400a3a2dbb7eb82099d6c8b92c8f
Author: Daniel Borkmann <daniel@iogearbox.net>

bpftool: Support ML-DSA program signing

This commit adds support for ML-DSA program signing in bpftool. It handles
OpenSSL versions that require signedAttrs by dropping the CMS_NOATTR flag
and bumps the maximum signature size to 16 KiB to accommodate larger ML-DSA
signatures.

> diff --git a/tools/bpf/bpftool/sign.c b/tools/bpf/bpftool/sign.c
> index 88726a6db6d0e..1b5502f48add0 100644
> --- a/tools/bpf/bpftool/sign.c
> +++ b/tools/bpf/bpftool/sign.c
[ ... ]
> @@ -167,6 +170,21 @@ int bpftool_prog_sign(struct bpf_load_and_run_opts *opts)
>  		goto cleanup;
>  	}
>  
> +#if OPENSSL_VERSION_NUMBER >= 0x30000000L && OPENSSL_VERSION_NUMBER < 0x40000000L
> +	if (EVP_PKEY_is_a(private_key, "ML-DSA-44") ||
> +	    EVP_PKEY_is_a(private_key, "ML-DSA-65") ||
> +	    EVP_PKEY_is_a(private_key, "ML-DSA-87")) {
> +		/*
> +		 * ML-DSA + CMS_NOATTR is not supported before openssl-4.0, so
> +		 * fall back to signedAttrs. ML-DSA does its own hashing and
> +		 * ignores the CMS digest, except when signedAttrs are used,
> +		 * where only SHA-512 is permitted.
> +		 */
> +		signer_flags &= ~CMS_NOATTR;

[Severity: Medium]
When CMS_NOATTR is cleared here, doesn't OpenSSL automatically include the
signingTime attribute by default?

If signingTime is included, this would cause the generated BPF signature to
change on every invocation. Could this break reproducible builds for projects
compiling signed BPF skeletons? Should CMS_NO_SIGNING_TIME be added to
signer_flags when CMS_NOATTR is cleared, similar to how scripts/sign-file.c
handles it?

> +		cms_digest = EVP_sha512();
> +	}
> +#endif
> +
>  	cms = CMS_sign(NULL, NULL, NULL, NULL,
>  		       CMS_NOCERTS | CMS_PARTIAL | CMS_BINARY | CMS_DETACHED |
>  			       CMS_STREAM);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260825142530.1329706-1-daniel@iogearbox.net?part=4