[xdp-hints] Re: [PATCH bpf-next v2 2/8] bpf: XDP metadata RX kfuncs

[Stanislav Fomichev <sdf@google.com>]

On Wed, Nov 23, 2022 at 6:24 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> >  static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> >                           struct bpf_insn *insn_buf, int insn_idx, int *cnt)
> >  {
> > @@ -15181,6 +15200,15 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> >               return -EINVAL;
> >       }
> >
> > +     if (resolve_prog_type(env->prog) == BPF_PROG_TYPE_XDP) {
> > +             int imm = fixup_xdp_kfunc_call(env, insn->imm);
> > +
> > +             if (imm) {
> > +                     insn->imm = imm;
> > +                     return 0;
>
> This needs to also set *cnt = 0 before returning; otherwise the verifier
> can do some really weird instruction rewriting that leads to the JIT
> barfing on invalid instructions (as I just found out while trying to
> test this).

Oops, that was me not paying too much attention during the merge..
Yonghong actually did some kfunc unrolling, yay :-)