Re: [PATCH] bpf, libbpf: reject non-exclusive metadata maps in the signed loader

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Tue May 19, 2026 at 8:00 PM PDT, KP Singh wrote:
> On Wed, May 20, 2026 at 1:17 AM <sashiko-bot@kernel.org> wrote:
>>
>> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
>> - [High] The generated BPF loader program uses a hardcoded 8-byte read (BPF_DW) to access the `excl_prog_sha` pointer field, which causes the BPF verifier to reject the loader on 32-bit architectures and silently bypasses the exclusivity check.
>
> I plan to move this to the kernel with a kfunc anyways. Any
> suggestions for the 32 bit fix (apart from an ugly union in bpf_map).

Use _bpf_md_ptr(). It's a normal pattern.

>> - [High] Branch target offset calculation is off-by-one, causing the jump target to land past the beginning of the cleanup block.
>> --
>
> Yeah this is valid:
>
>  Compute the cleanup-label offset after emitting the MOV that sets the
>   error code in R7. Otherwise the JMP lands one insn past cleanup_label
>   and skips the first FD-close, matching the emit_check_err() pattern.
>
> diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
> index becfda5b9025..6950443ba698 100644
> --- a/tools/lib/bpf/gen_loader.c
> +++ b/tools/lib/bpf/gen_loader.c
> @@ -592,9 +592,9 @@ 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;
> +               emit(gen, BPF_MOV64_IMM(BPF_REG_7, -EINVAL));
> +               off = -(gen->insn_cur - gen->insn_start -
> gen->cleanup_label) / 8 - 1;
>                 if (is_simm16(off)) {
> -                       emit(gen, BPF_MOV64_IMM(BPF_REG_7, -EINVAL));

maybe fix the math instead of moving this emit ?
Also split the fix into pre-patch.

>                         emit(gen, BPF_JMP_REG(BPF_JNE, BPF_REG_2,
> BPF_REG_3, off));
>                 } else {
>                         gen->error = -ERANGE;

and while at it remove redundant 'emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, -1));'

pw-bot: cr