xdp: Sample xdp program implementing ip forward

Implements port to port forwarding with route table and arp table
lookup for ipv4 packets using bpf_redirect helper function and
lpm_trie  map.
Signed-off-by: Christina Jacob <Christina.Jacob@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

samples/bpf/Makefile

@@ -29,6 +29,7 @@ hostprogs-y += test_cgrp2_sock
 hostprogs-y += test_cgrp2_sock2
 hostprogs-y += xdp1
 hostprogs-y += xdp2
+hostprogs-y += xdp_router_ipv4
 hostprogs-y += test_current_task_under_cgroup
 hostprogs-y += trace_event
 hostprogs-y += sampleip
@@ -76,6 +77,7 @@ test_cgrp2_sock2-objs := bpf_load.o $(LIBBPF) test_cgrp2_sock2.o
 xdp1-objs := bpf_load.o $(LIBBPF) xdp1_user.o
 # reuse xdp1 source intentionally
 xdp2-objs := bpf_load.o $(LIBBPF) xdp1_user.o
+xdp_router_ipv4-objs := bpf_load.o $(LIBBPF) xdp_router_ipv4_user.o
 test_current_task_under_cgroup-objs := bpf_load.o $(LIBBPF) $(CGROUP_HELPERS) \
 				       test_current_task_under_cgroup_user.o
 trace_event-objs := bpf_load.o $(LIBBPF) trace_event_user.o
@@ -118,6 +120,7 @@ always += parse_varlen.o parse_simple.o parse_ldabs.o
 always += test_cgrp2_tc_kern.o
 always += xdp1_kern.o
 always += xdp2_kern.o
+always += xdp_router_ipv4_kern.o
 always += test_current_task_under_cgroup_kern.o
 always += trace_event_kern.o
 always += sampleip_kern.o
@@ -166,6 +169,7 @@ HOSTLOADLIBES_map_perf_test += -lelf -lrt
 HOSTLOADLIBES_test_overhead += -lelf -lrt
 HOSTLOADLIBES_xdp1 += -lelf
 HOSTLOADLIBES_xdp2 += -lelf
+HOSTLOADLIBES_xdp_router_ipv4 += -lelf
 HOSTLOADLIBES_test_current_task_under_cgroup += -lelf
 HOSTLOADLIBES_trace_event += -lelf
 HOSTLOADLIBES_sampleip += -lelf

samples/bpf/xdp_router_ipv4_kern.c

+/* Copyright (C) 2017 Cavium, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ */
+#define KBUILD_MODNAME "foo"
+#include <uapi/linux/bpf.h>
+#include <linux/in.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include "bpf_helpers.h"
+#include <linux/slab.h>
+#include <net/ip_fib.h>
+
+struct trie_value {
+	__u8 prefix[4];
+	__be64 value;
+	int ifindex;
+	int metric;
+	__be32 gw;
+};
+
+/* Key for lpm_trie*/
+union key_4 {
+	u32 b32[2];
+	u8 b8[8];
+};
+
+struct arp_entry {
+	__be64 mac;
+	__be32 dst;
+};
+
+struct direct_map {
+	struct arp_entry arp;
+	int ifindex;
+	__be64 mac;
+};
+
+/* Map for trie implementation*/
+struct bpf_map_def SEC("maps") lpm_map = {
+	.type = BPF_MAP_TYPE_LPM_TRIE,
+	.key_size = 8,
+	.value_size = sizeof(struct trie_value),
+	.max_entries = 50,
+	.map_flags = BPF_F_NO_PREALLOC,
+};
+
+/* Map for counter*/
+struct bpf_map_def SEC("maps") rxcnt = {
+	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size = sizeof(u32),
+	.value_size = sizeof(u64),
+	.max_entries = 256,
+};
+
+/* Map for ARP table*/
+struct bpf_map_def SEC("maps") arp_table = {
+	.type = BPF_MAP_TYPE_HASH,
+	.key_size = sizeof(__be32),
+	.value_size = sizeof(__be64),
+	.max_entries = 50,
+};
+
+/* Map to keep the exact match entries in the route table*/
+struct bpf_map_def SEC("maps") exact_match = {
+	.type = BPF_MAP_TYPE_HASH,
+	.key_size = sizeof(__be32),
+	.value_size = sizeof(struct direct_map),
+	.max_entries = 50,
+};
+
+struct bpf_map_def SEC("maps") tx_port = {
+	.type = BPF_MAP_TYPE_DEVMAP,
+	.key_size = sizeof(int),
+	.value_size = sizeof(int),
+	.max_entries = 100,
+};
+
+/* Function to set source and destination mac of the packet */
+static inline void set_src_dst_mac(void *data, void *src, void *dst)
+{
+	unsigned short *source = src;
+	unsigned short *dest  = dst;
+	unsigned short *p = data;
+
+	__builtin_memcpy(p, dest, 6);
+	__builtin_memcpy(p + 3, source, 6);
+}
+
+/* Parse IPV4 packet to get SRC, DST IP and protocol */
+static inline int parse_ipv4(void *data, u64 nh_off, void *data_end,
+			     __be32 *src, __be32 *dest)
+{
+	struct iphdr *iph = data + nh_off;
+
+	if (iph + 1 > data_end)
+		return 0;
+	*src = iph->saddr;
+	*dest = iph->daddr;
+	return iph->protocol;
+}
+
+SEC("xdp_router_ipv4")
+int xdp_router_ipv4_prog(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	__be64 *dest_mac = NULL, *src_mac = NULL;
+	void *data = (void *)(long)ctx->data;
+	struct trie_value *prefix_value;
+	int rc = XDP_DROP, forward_to;
+	struct ethhdr *eth = data;
+	union key_4 key4;
+	long *value;
+	u16 h_proto;
+	u32 ipproto;
+	u64 nh_off;
+
+	nh_off = sizeof(*eth);
+	if (data + nh_off > data_end)
+		return rc;
+
+	h_proto = eth->h_proto;
+
+	if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
+		struct vlan_hdr *vhdr;
+
+		vhdr = data + nh_off;
+		nh_off += sizeof(struct vlan_hdr);
+		if (data + nh_off > data_end)
+			return rc;
+		h_proto = vhdr->h_vlan_encapsulated_proto;
+	}
+	if (h_proto == htons(ETH_P_ARP)) {
+		return XDP_PASS;
+	} else if (h_proto == htons(ETH_P_IP)) {
+		struct direct_map *direct_entry;
+		__be32 src_ip = 0, dest_ip = 0;
+
+		ipproto = parse_ipv4(data, nh_off, data_end, &src_ip, &dest_ip);
+		direct_entry = bpf_map_lookup_elem(&exact_match, &dest_ip);
+		/* Check for exact match, this would give a faster lookup*/
+		if (direct_entry && direct_entry->mac && direct_entry->arp.mac) {
+			src_mac = &direct_entry->mac;
+			dest_mac = &direct_entry->arp.mac;
+			forward_to = direct_entry->ifindex;
+		} else {
+			/* Look up in the trie for lpm*/
+			key4.b32[0] = 32;
+			key4.b8[4] = dest_ip & 0xff;
+			key4.b8[5] = (dest_ip >> 8) & 0xff;
+			key4.b8[6] = (dest_ip >> 16) & 0xff;
+			key4.b8[7] = (dest_ip >> 24) & 0xff;
+			prefix_value = bpf_map_lookup_elem(&lpm_map, &key4);
+			if (!prefix_value)
+				return XDP_DROP;
+			src_mac = &prefix_value->value;
+			if (!src_mac)
+				return XDP_DROP;
+			dest_mac = bpf_map_lookup_elem(&arp_table, &dest_ip);
+			if (!dest_mac) {
+				if (!prefix_value->gw)
+					return XDP_DROP;
+				dest_ip = prefix_value->gw;
+				dest_mac = bpf_map_lookup_elem(&arp_table, &dest_ip);
+			}
+			forward_to = prefix_value->ifindex;
+		}
+	} else {
+		ipproto = 0;
+	}
+	if (src_mac && dest_mac) {
+		set_src_dst_mac(data, src_mac, dest_mac);
+		value = bpf_map_lookup_elem(&rxcnt, &ipproto);
+		if (value)
+			*value += 1;
+		return  bpf_redirect_map(&tx_port, forward_to, 0);
+	}
+	return rc;
+}
+
+char _license[] SEC("license") = "GPL";