xref: /openbmc/linux/samples/bpf/xdp_fwd_kern.c (revision 98ddec80)
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_helpers.h"
23 
24 #define IPV6_FLOWINFO_MASK              cpu_to_be32(0x0FFFFFFF)
25 
26 struct bpf_map_def SEC("maps") tx_port = {
27 	.type = BPF_MAP_TYPE_DEVMAP,
28 	.key_size = sizeof(int),
29 	.value_size = sizeof(int),
30 	.max_entries = 64,
31 };
32 
33 /* from include/net/ip.h */
34 static __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 
43 static __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 	int out_index;
52 	u16 h_proto;
53 	u64 nh_off;
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 	out_index = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
105 
106 	/* verify egress index has xdp support
107 	 * TO-DO bpf_map_lookup_elem(&tx_port, &key) fails with
108 	 *       cannot pass map_type 14 into func bpf_map_lookup_elem#1:
109 	 * NOTE: without verification that egress index supports XDP
110 	 *       forwarding packets are dropped.
111 	 */
112 	if (out_index > 0) {
113 		if (h_proto == htons(ETH_P_IP))
114 			ip_decrease_ttl(iph);
115 		else if (h_proto == htons(ETH_P_IPV6))
116 			ip6h->hop_limit--;
117 
118 		memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
119 		memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
120 		return bpf_redirect_map(&tx_port, out_index, 0);
121 	}
122 
123 	return XDP_PASS;
124 }
125 
126 SEC("xdp_fwd")
127 int xdp_fwd_prog(struct xdp_md *ctx)
128 {
129 	return xdp_fwd_flags(ctx, 0);
130 }
131 
132 SEC("xdp_fwd_direct")
133 int xdp_fwd_direct_prog(struct xdp_md *ctx)
134 {
135 	return xdp_fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
136 }
137 
138 char _license[] SEC("license") = "GPL";
139