xdp: T2666: initial XDP (generic mode) forwarding support

The CLI command 'set interfaces ethernet <interface> offload-options xdp" enables
the XDP generic mode on the given interface.

vyos@vyos:~$ show interfaces ethernet eth1
eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 xdpgeneric/id:151 qdisc mq state DOWN group default qlen 1000
    link/ether 00:50:56:bf:ef:aa brd ff:ff:ff:ff:ff:ff
    inet6 fe80::250:56ff:febf:efaa/64 scope link tentative
       valid_lft forever preferred_lft forever
    Description: fooa

XDP code is thankfully copied from [1], thank you for this nice tutorial.

NOTE: this is an experimental feature which might break your
forwarding/filtering.

[1]: https://medium.com/swlh/building-a-xdp-express-data-path-based-peering-router-20db4995da66

1 files changed, 97 insertions, 0 deletions

diff --git a/src/ebpf/xdp_drop_ebpf.c b/src/ebpf/xdp_drop_ebpf.c
new file mode 100644
index 000000000..a08edf58d
--- /dev/null
+++ b/src/ebpf/xdp_drop_ebpf.c
@@ -0,0 +1,97 @@
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/udp.h>
+
+#include <stdint.h>
+
+/* IP flags. */
+#define IP_CE     0x8000    /* Flag: "Congestion"     */
+#define IP_DF     0x4000    /* Flag: "Don't Fragment" */
+#define IP_MF     0x2000    /* Flag: "More Fragments" */
+#define IP_OFFSET 0x1FFF    /* "Fragment Offset" part */
+
+#define SEC(NAME) __attribute__((section(NAME), used))
+
+#define htons(x) ((__be16)___constant_swab16((x)))
+#define htonl(x) ((__be32)___constant_swab32((x)))
+
+struct vlan_hdr {
+  __be16 h_vlan_TCI;
+  __be16 h_vlan_encapsulated_proto;
+};
+
+SEC("prog")
+int xdp_drop(struct xdp_md *ctx) {
+  void *data_end = (void *)(long)ctx->data_end;
+  void *data = (void *)(long)ctx->data;
+  struct ethhdr *eth = data;
+
+  uint64_t nh_off = sizeof(*eth);
+  if (data + nh_off > data_end) {
+    return XDP_PASS;
+  }
+
+  uint16_t h_proto = eth->h_proto;
+  int i;
+
+  /* Handle double VLAN tagged packet. See https://en.wikipedia.org/wiki/IEEE_802.1ad */
+  for (i = 0; i < 2; i++) {
+    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 XDP_PASS;
+      }
+      h_proto = vhdr->h_vlan_encapsulated_proto;
+    }
+  }
+
+  if (h_proto == htons(ETH_P_IP)) {
+    struct iphdr *iph = data + nh_off;
+    struct udphdr *udph = data + nh_off + sizeof(struct iphdr);
+
+    uint32_t hostid = iph->daddr >> 24;
+
+    if (udph + 1 > (struct udphdr *)data_end) {
+      return XDP_PASS;
+    }
+    if (hostid == 0 || hostid == 255) {
+      return XDP_DROP;
+    }
+    if (iph->frag_off & htons(IP_MF | IP_OFFSET)) {
+      return XDP_DROP;
+    }
+    if (iph->protocol == IPPROTO_UDP) {
+      __be16 dport = htons(udph->dest);
+      __be16 sport = htons(udph->source);
+
+      if (dport == 53 || sport == 53) {
+        return XDP_DROP;
+      }
+    }
+  } else if (h_proto == htons(ETH_P_IPV6)) {
+    struct ipv6hdr *ip6h = data + nh_off;
+    struct udphdr *udph = data + nh_off + sizeof(struct ipv6hdr);
+
+    if (udph + 1 > (struct udphdr *)data_end) {
+      return XDP_PASS;
+    }
+    if (ip6h->nexthdr == IPPROTO_UDP) {
+      __be16 dport = htons(udph->dest);
+      __be16 sport = htons(udph->source);
+
+      if (dport == 53 || sport == 53) {
+        return XDP_DROP;
+      }
+    }
+  }
+
+  return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";