Tizian-Maxime-Weigt/l3-l4-forwarding-in-xdp
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Adding the xdp based fwd engine

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Tizian Maxime Weigt 2025-10-27 16:02:36 +00:00
parent ebae81a091
commit 0bc9ea0685
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// SPDX-License-Identifier: GPL-2.0
/* Example of L3 forwarding via XDP and use of bpf FIB lookup helper.
*
* Copyright (c) 2017-18 David Ahern <dsahern@gmail.com>
*/
#define KBUILD_MODNAME "xdp_l3fwd"
#include <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/bpf_helpers.h>
#define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF)
struct bpf_map_def SEC("maps") xdp_l3fwd_ports = {
.type = BPF_MAP_TYPE_DEVMAP,
.key_size = sizeof(int),
.value_size = sizeof(int),
.max_entries = 512,
};
/* from include/net/ip.h */
static __always_inline int ip_decrease_ttl(struct iphdr *iph)
{
u32 check = (__force u32)iph->check;
check += (__force u32)htons(0x0100);
iph->check = (__force __sum16)(check + (check >= 0xFFFF));
return --iph->ttl;
}
static __always_inline int xdp_l3fwd_flags(struct xdp_md *ctx, u32 flags)
{
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
struct bpf_fib_lookup fib_params;
struct ethhdr *eth = data;
struct ipv6hdr *ip6h;
struct iphdr *iph;
u16 h_proto;
u64 nh_off;
int rc;
nh_off = sizeof(*eth);
if (data + nh_off > data_end)
return XDP_DROP;
__builtin_memset(&fib_params, 0, sizeof(fib_params));
h_proto = eth->h_proto;
if (h_proto == htons(ETH_P_IP)) {
iph = data + nh_off;
if (iph + 1 > data_end)
return XDP_DROP;
if (iph->ttl <= 1)
return XDP_PASS;
fib_params.family = AF_INET;
fib_params.tos = iph->tos;
fib_params.l4_protocol = iph->protocol;
fib_params.tot_len = ntohs(iph->tot_len);
fib_params.ipv4_src = iph->saddr;
fib_params.ipv4_dst = iph->daddr;
} else if (h_proto == htons(ETH_P_IPV6)) {
struct in6_addr *src = (struct in6_addr *) fib_params.ipv6_src;
struct in6_addr *dst = (struct in6_addr *) fib_params.ipv6_dst;
ip6h = data + nh_off;
if (ip6h + 1 > data_end)
return XDP_DROP;
if (ip6h->hop_limit <= 1)
return XDP_PASS;
fib_params.family = AF_INET6;
fib_params.flowinfo = *(__be32 *)ip6h & IPV6_FLOWINFO_MASK;
fib_params.l4_protocol = ip6h->nexthdr;
fib_params.tot_len = ntohs(ip6h->payload_len);
*src = ip6h->saddr;
*dst = ip6h->daddr;
} else {
return XDP_PASS;
}
fib_params.ifindex = ctx->ingress_ifindex;
rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
if (!bpf_map_lookup_elem(&xdp_l3fwd_ports, &fib_params.ifindex))
return XDP_PASS;
if (h_proto == htons(ETH_P_IP))
ip_decrease_ttl(iph);
else if (h_proto == htons(ETH_P_IPV6))
ip6h->hop_limit--;
__builtin_memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
__builtin_memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
return bpf_redirect_map(&xdp_l3fwd_ports, fib_params.ifindex, 0);
}
return XDP_PASS;
}
SEC("xdp_l3fwd")
int xdp_l3fwd_prog(struct xdp_md *ctx)
{
return xdp_l3fwd_flags(ctx, 0);
}
SEC("xdp_l3fwd_direct")
int xdp_l3fwd_direct_prog(struct xdp_md *ctx)
{
return xdp_l3fwd_flags(ctx, BPF_FIB_LOOKUP_DIRECT);
}
char _license[] SEC("license") = "GPL";