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

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Message-ID: <87a64hvje0.fsf@toke.dk>
Date:   Wed, 23 Nov 2022 15:24:23 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>, bpf@...r.kernel.org
Cc:     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, sdf@...gle.com,
        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

>  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).

-Toke