af_xdp.bpf.c

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/*
 * SPDX-License-Identifier: GPL-2.0 OR Apache-2.0
 * Dual-licensed under GPL version 2.0 or Apache License version 2.0
 * Copyright (c) 2020 Cisco and/or its affiliates.
 */
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <bpf/bpf_helpers.h>

/*
 * when compiled, debug print can be viewed with eg.
 * sudo cat /sys/kernel/debug/tracing/trace_pipe
 */
#ifdef DEBUG
#define s__(n)   # n
#define s_(n)    s__(n)
#define x_(fmt)  __FILE__ ":" s_(__LINE__) ": " fmt "\n"
#define DEBUG_PRINT_(fmt, ...) do { \
    const char fmt__[] = fmt; \
    bpf_trace_printk(fmt__, sizeof(fmt), ## __VA_ARGS__); } while(0)
#define DEBUG_PRINT(fmt, ...)   DEBUG_PRINT_ (x_(fmt), ## __VA_ARGS__)
#else   /* DEBUG */
#define DEBUG_PRINT(fmt, ...)
#endif  /* DEBUG */

#define ntohs(x)        __constant_ntohs(x)

SEC("maps")
struct bpf_map_def xsks_map = {
    .type = BPF_MAP_TYPE_XSKMAP,
    .key_size = sizeof(int),
    .value_size = sizeof(int),
    .max_entries = 64, /* max 64 queues per device */
};

SEC("xdp_sock")
int xdp_sock_prog(struct xdp_md *ctx) {
    const void *data = (void *)(long)ctx->data;
    const void *data_end = (void *)(long)ctx->data_end;

    DEBUG_PRINT("rx %ld bytes packet", (long)data_end - (long)data);

    /* smallest packet we are interesting in is ip-ip */
    if (data + sizeof(struct ethhdr) + 2 * sizeof(struct iphdr) > data_end) {
        DEBUG_PRINT("packet too small");
        return XDP_PASS;
    }

    const struct ethhdr *eth = data;
    if (eth->h_proto != ntohs(ETH_P_IP)) {
        DEBUG_PRINT("unsupported eth proto %x", (int)eth->h_proto);
        return XDP_PASS;
    }

    const struct iphdr *ip = (void *)(eth + 1);
    switch (ip->protocol) {
      case IPPROTO_UDP: {
            const struct udphdr *udp = (void *)(ip + 1);
            if (udp->dest != ntohs(4789)) { /* VxLAN dest port */
                DEBUG_PRINT("unsupported udp dst port %x", (int)udp->dest);
                return XDP_PASS;
            }
          }
      case IPPROTO_IPIP:
      case IPPROTO_ESP:
        break;
      default:
        DEBUG_PRINT("unsupported ip proto %x", (int)ip->protocol);
        return XDP_PASS;
    }

    int qid = ctx->rx_queue_index;
    if (!bpf_map_lookup_elem(&xsks_map, &qid))
      {
        DEBUG_PRINT("no socket found");
        return XDP_PASS;
      }

    DEBUG_PRINT("going to socket %d", qid);
    return bpf_redirect_map(&xsks_map, qid, 0);
}

/* actually Dual GPLv2/Apache2, but GPLv2 as far as kernel is concerned */
SEC("license")
char _license[] = "GPL";