netdev - Re: [PATCHv9 bpf-next 2/5] xdp: add a new helper for dev map multicast support

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Date:   Sat, 29 Aug 2020 00:05:42 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Hangbin Liu <liuhangbin@...il.com>, bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jiri Benc <jbenc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Andrii Nakryiko B <andrii.nakryiko@...il.com>
Subject: Re: [PATCHv9 bpf-next 2/5] xdp: add a new helper for dev map
 multicast support

On 8/26/20 3:19 PM, Hangbin Liu wrote:
[...]
> +BPF_CALL_3(bpf_xdp_redirect_map_multi, struct bpf_map *, map,
> +	   struct bpf_map *, ex_map, u64, flags)
> +{
> +	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> +
> +	/* Limit ex_map type to DEVMAP_HASH to get better performance */
> +	if (unlikely(!map ||

Why is test on !map needed when arg1_type is ARG_CONST_MAP_PTR? Verifier must
guarantee that it's a valid map ptr .. are you saying this is not the case for
this helper?

> +		     (ex_map && ex_map->map_type != BPF_MAP_TYPE_DEVMAP_HASH) ||
> +		     flags & ~BPF_F_EXCLUDE_INGRESS))
> +		return XDP_ABORTED;
> +
> +	ri->tgt_index = 0;
> +	/* Set the tgt_value to NULL to distinguish with bpf_xdp_redirect_map */
> +	ri->tgt_value = NULL;
> +	ri->flags = flags;
> +	ri->ex_map = ex_map;
> +
> +	WRITE_ONCE(ri->map, map);
> +
> +	return XDP_REDIRECT;
> +}
> +
> +static const struct bpf_func_proto bpf_xdp_redirect_map_multi_proto = {
> +	.func           = bpf_xdp_redirect_map_multi,
> +	.gpl_only       = false,
> +	.ret_type       = RET_INTEGER,
> +	.arg1_type      = ARG_CONST_MAP_PTR,
> +	.arg2_type      = ARG_CONST_MAP_PTR_OR_NULL,
> +	.arg3_type      = ARG_ANYTHING,
> +};
> +
>   static unsigned long bpf_skb_copy(void *dst_buff, const void *skb,
>   				  unsigned long off, unsigned long len)
>   {
> @@ -6833,6 +6933,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   		return &bpf_xdp_redirect_proto;
>   	case BPF_FUNC_redirect_map:
>   		return &bpf_xdp_redirect_map_proto;
> +	case BPF_FUNC_redirect_map_multi:
> +		return &bpf_xdp_redirect_map_multi_proto;
>   	case BPF_FUNC_xdp_adjust_tail:
>   		return &bpf_xdp_adjust_tail_proto;
>   	case BPF_FUNC_fib_lookup: