[PATCH bpf v3 1/2] libbpf: fix off-by-one in emit_signature_match jump offset

[bot+bpf-ci at kernel.org]

> Fixes: fb2b0e290147 ("libbpf: Update light skeleton for signing")

Daniel Borkmann reviewed v2 and pointed out that the Fixes tag
references the wrong commit. The commit fb2b0e290147 only modified
tools/lib/bpf/skel_internal.h and did not touch emit_signature_match.
He suggested using ea923080c145 ("libbpf: Embed and verify the
metadata hash in the loader") instead.

Reference: https://lore.kernel.org/bpf/a9345efb-b691-4fc1-9bad-d571bd324c25@iogearbox.net/

The search for the correct Fixes tag confirmed that fb2b0e290147 did
not introduce the emit_signature_match function or the buggy jump
offset calculation in tools/lib/bpf/gen_loader.c. The true origin
commit could not be determined in this repository's history.

Should the Fixes tag be updated to point to the commit that actually
introduced the emit_signature_match function with the buggy offset
calculation?

> diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
> index cd5c2543f54d..9478b8f78f26 100644
> --- a/tools/lib/bpf/gen_loader.c
> +++ b/tools/lib/bpf/gen_loader.c
> @@ -592,13 +592,12 @@ static void emit_signature_match(struct bpf_gen *gen)
>  		gen->hash_insn_offset[i] = gen->insn_cur - gen->insn_start;
>  		emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_3, 0, 0, 0, 0, 0));
>
> -		off =  -(gen->insn_cur - gen->insn_start - gen->cleanup_label) / 8 - 1;
> +		off = -(gen->insn_cur - gen->insn_start - gen->cleanup_label) / 8 - 2;
>  		if (is_simm16(off)) {
>  			emit(gen, BPF_MOV64_IMM(BPF_REG_7, -EINVAL));
>  			emit(gen, BPF_JMP_REG(BPF_JNE, BPF_REG_2, BPF_REG_3, off));
>  		} else {
>  			gen->error = -ERANGE;
> -			emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, -1));
>  		}
>  	}
>  }


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/26314489328