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

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Date:   Wed, 23 Nov 2022 10:43:16 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        haoluo@...gle.com, jolsa@...nel.org,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        netdev@...r.kernel.org
Subject: Re: [xdp-hints] [PATCH bpf-next v2 2/8] bpf: XDP metadata RX kfuncs

On Wed, Nov 23, 2022 at 6:24 AM Toke Høiland-Jørgensen <toke@...hat.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 :-)