LXR linux/samples/bpf/xdp_fwd

   1// SPDX-License-Identifier: GPL-2.0
   2/* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com>
   3 *
   4 * This program is free software; you can redistribute it and/or
   5 * modify it under the terms of version 2 of the GNU General Public
   6 * License as published by the Free Software Foundation.
   7 *
   8 * This program is distributed in the hope that it will be useful, but
   9 * WITHOUT ANY WARRANTY; without even the implied warranty of
  10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  11 * General Public License for more details.
  12 */
  13#define KBUILD_MODNAME "foo"
  14#include <uapi/linux/bpf.h>
  15#include <linux/in.h>
  16#include <linux/if_ether.h>
  17#include <linux/if_packet.h>
  18#include <linux/if_vlan.h>
  19#include <linux/ip.h>
  20#include <linux/ipv6.h>
  21
  22#include <bpf/bpf_helpers.h>
  23
  24#define IPV6_FLOWINFO_MASK              cpu_to_be32(0x0FFFFFFF)
  25
  26struct {
  27        __uint(type, BPF_MAP_TYPE_DEVMAP);
  28        __uint(key_size, sizeof(int));
  29        __uint(value_size, sizeof(int));
  30        __uint(max_entries, 64);
  31} xdp_tx_ports SEC(".maps");
  32
  33/* from include/net/ip.h */
  34static __always_inline int ip_decrease_ttl(struct iphdr *iph)
  35{
  36        u32 check = (__force u32)iph->check;
  37
  38        check += (__force u32)htons(0x0100);
  39        iph->check = (__force __sum16)(check + (check >= 0xFFFF));
  40        return --iph->ttl;
  41}
  42
  43static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags)
  44{
  45        void *data_end = (void *)(long)ctx->data_end;
  46        void *data = (void *)(long)ctx->data;
  47        struct bpf_fib_lookup fib_params;
  48        struct ethhdr *eth = data;
  49        struct ipv6hdr *ip6h;
  50        struct iphdr *iph;
  51        u16 h_proto;
  52        u64 nh_off;
  53        int rc;
  54
  55        nh_off = sizeof(*eth);
  56        if (data + nh_off > data_end)
  57                return XDP_DROP;
  58
  59        __builtin_memset(&fib_params, 0, sizeof(fib_params));
  60
  61        h_proto = eth->h_proto;
  62        if (h_proto == htons(ETH_P_IP)) {
  63                iph = data + nh_off;
  64
  65                if (iph + 1 > data_end)
  66                        return XDP_DROP;
  67
  68                if (iph->ttl <= 1)
  69                        return XDP_PASS;
  70
  71                fib_params.family       = AF_INET;
  72                fib_params.tos          = iph->tos;
  73                fib_params.l4_protocol  = iph->protocol;
  74                fib_params.sport        = 0;
  75                fib_params.dport        = 0;
  76                fib_params.tot_len      = ntohs(iph->tot_len);
  77                fib_params.ipv4_src     = iph->saddr;
  78                fib_params.ipv4_dst     = iph->daddr;
  79        } else if (h_proto == htons(ETH_P_IPV6)) {
  80                struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
  81                struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
  82
  83                ip6h = data + nh_off;
  84                if (ip6h + 1 > data_end)
  85                        return XDP_DROP;
  86
  87                if (ip6h->hop_limit <= 1)
  88                        return XDP_PASS;
  89
  90                fib_params.family       = AF_INET6;
  91                fib_params.flowinfo     = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
  92                fib_params.l4_protocol  = ip6h->nexthdr;
  93                fib_params.sport        = 0;
  94                fib_params.dport        = 0;
  95                fib_params.tot_len      = ntohs(ip6h->payload_len);
  96                *src                    = ip6h->saddr;
  97                *dst                    = ip6h->daddr;
  98        } else {
  99                return XDP_PASS;
 100        }
 101
 102        fib_params.ifindex = ctx->ingress_ifindex;
 103
 104        rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
 105        /*
 106         * Some rc (return codes) from bpf_fib_lookup() are important,
 107         * to understand how this XDP-prog interacts with network stack.
 108         *
 109         * BPF_FIB_LKUP_RET_NO_NEIGH:
 110         *  Even if route lookup was a success, then the MAC-addresses are also
 111         *  needed.  This is obtained from arp/neighbour table, but if table is
 112         *  (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned.  To avoid
 113         *  doing ARP lookup directly from XDP, then send packet to normal
 114         *  network stack via XDP_PASS and expect it will do ARP resolution.
 115         *
 116         * BPF_FIB_LKUP_RET_FWD_DISABLED:
 117         *  The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding
 118         *  setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not
 119         *  enabled this on ingress device.
 120         */
 121        if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
 122                /* Verify egress index has been configured as TX-port.
 123                 * (Note: User can still have inserted an egress ifindex that
 124                 * doesn't support XDP xmit, which will result in packet drops).
 125                 *
 126                 * Note: lookup in devmap supported since 0cdbb4b09a0.
 127                 * If not supported will fail with:
 128                 *  cannot pass map_type 14 into func bpf_map_lookup_elem#1:
 129                 */
 130                if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))
 131                        return XDP_PASS;
 132
 133                if (h_proto == htons(ETH_P_IP))
 134                        ip_decrease_ttl(iph);
 135                else if (h_proto == htons(ETH_P_IPV6))
 136                        ip6h->hop_limit--;
 137
 138                memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
 139                memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
 140                return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);
 141        }
 142
 143        return XDP_PASS;
 144}
 145
 146SEC("xdp_fwd")
 147int xdp_fwd_prog(struct xdp_md *ctx)
 148{
 149        return xdp_fwd_flags(ctx, 0);
 150}
 151
 152SEC("xdp_fwd_direct")
 153int xdp_fwd_direct_prog(struct xdp_md *ctx)
 154{
 155        return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
 156}
 157
 158char _license[] SEC("license") = "GPL";
 159