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-rw-r--r--src/libknot/xdp/bpf-kernel.c293
1 files changed, 293 insertions, 0 deletions
diff --git a/src/libknot/xdp/bpf-kernel.c b/src/libknot/xdp/bpf-kernel.c
new file mode 100644
index 0000000..97192bc
--- /dev/null
+++ b/src/libknot/xdp/bpf-kernel.c
@@ -0,0 +1,293 @@
+/* Copyright (C) 2022 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
+#include <linux/udp.h>
+#include <bpf/bpf_endian.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf-consts.h"
+
+/* Don't fragment flag. */
+#define IP_DF 0x4000
+
+#define AF_INET 2
+#define AF_INET6 10
+
+/* Define maximum reasonable number of NIC queues supported. */
+#define QUEUE_MAX 256
+
+/* A map of configuration options. */
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __uint(max_entries, QUEUE_MAX);
+ __uint(key_size, sizeof(__u32)); /* Must be 4 bytes. */
+ __uint(value_size, sizeof(knot_xdp_opts_t));
+} opts_map SEC(".maps");
+
+/* A map of AF_XDP sockets. */
+struct {
+ __uint(type, BPF_MAP_TYPE_XSKMAP);
+ __uint(max_entries, QUEUE_MAX);
+ __uint(key_size, sizeof(__u32)); /* Must be 4 bytes. */
+ __uint(value_size, sizeof(int));
+} xsks_map SEC(".maps");
+
+struct ipv6_frag_hdr {
+ unsigned char nexthdr;
+ unsigned char whatever[7];
+} __attribute__((packed));
+
+SEC("xdp")
+int xdp_redirect_dns_func(struct xdp_md *ctx)
+{
+ /* Get the queue options. */
+ __u32 index = ctx->rx_queue_index;
+ struct knot_xdp_opts *opts_ptr = bpf_map_lookup_elem(&opts_map, &index);
+ if (!opts_ptr) {
+ return XDP_ABORTED;
+ }
+ knot_xdp_opts_t opts = *opts_ptr;
+
+ /* Check if the filter is disabled. */
+ if (!(opts.flags & KNOT_XDP_FILTER_ON)) {
+ return XDP_PASS;
+ }
+
+ /* Try to reserve space in front of the packet for additional (VLAN) data. */
+ (void)bpf_xdp_adjust_meta(ctx, - (int)sizeof(struct knot_xdp_info)
+ - KNOT_XDP_PKT_ALIGNMENT);
+
+ void *data = (void *)(long)ctx->data;
+ const void *data_end = (void *)(long)ctx->data_end;
+ struct knot_xdp_info *meta = (void *)(long)ctx->data_meta;
+
+ /* Check if the meta data pointer is usable (e.g. not `tap` interface). */
+ if ((void *)meta + sizeof(*meta) > data) {
+ meta = 0;
+ }
+
+ struct ethhdr *eth_hdr = data;
+ const void *ip_hdr;
+ const struct iphdr *ip4;
+ const struct ipv6hdr *ip6;
+ const void *l4_hdr;
+ __u8 ipv4;
+ __u8 ip_proto;
+ __u8 fragmented = 0;
+ __u16 eth_type; /* In big endian. */
+
+ /* Parse Ethernet header. */
+ if ((void *)eth_hdr + sizeof(*eth_hdr) > data_end) {
+ return XDP_DROP;
+ }
+ data += sizeof(*eth_hdr);
+
+ /* Parse possible VLAN (802.1Q) header. */
+ if (eth_hdr->h_proto == __constant_htons(ETH_P_8021Q)) {
+ if (data + sizeof(__u16) + sizeof(eth_type) > data_end) {
+ return XDP_DROP;
+ } else if (meta == 0) { /* VLAN not supported. */
+ return XDP_PASS;
+ }
+ __builtin_memcpy(&eth_type, data + sizeof(__u16), sizeof(eth_type));
+ data += sizeof(__u16) + sizeof(eth_type);
+ } else {
+ eth_type = eth_hdr->h_proto;
+ }
+
+ ip_hdr = data;
+
+ /* Parse IPv4 or IPv6 header. */
+ switch (eth_type) {
+ case __constant_htons(ETH_P_IP):
+ ip4 = ip_hdr;
+ if ((void *)ip4 + sizeof(*ip4) > data_end) {
+ return XDP_DROP;
+ }
+ if (ip4->version != 4) {
+ return XDP_DROP;
+ }
+
+ /* Check the IP length. Cannot use strict equality due to
+ * Ethernet padding applied to frames shorter than 64 octects. */
+ if (data_end - data < __bpf_ntohs(ip4->tot_len)) {
+ return XDP_DROP;
+ }
+
+ if (ip4->frag_off != 0 &&
+ ip4->frag_off != __constant_htons(IP_DF)) {
+ fragmented = 1;
+ }
+ ip_proto = ip4->protocol;
+ l4_hdr = data + ip4->ihl * 4;
+ ipv4 = 1;
+ break;
+ case __constant_htons(ETH_P_IPV6):
+ ip6 = ip_hdr;
+ if ((void *)ip6 + sizeof(*ip6) > data_end) {
+ return XDP_DROP;
+ }
+ if (ip6->version != 6) {
+ return XDP_DROP;
+ }
+
+ /* Check the IP length. Cannot use strict equality due to
+ * Ethernet padding applied to frames shorter than 64 octects. */
+ if (data_end - data < __bpf_ntohs(ip6->payload_len) + sizeof(*ip6)) {
+ return XDP_DROP;
+ }
+
+ ip_proto = ip6->nexthdr;
+ data += sizeof(*ip6);
+ if (ip_proto == IPPROTO_FRAGMENT) {
+ fragmented = 1;
+ const struct ipv6_frag_hdr *frag = data;
+ if ((void *)frag + sizeof(*frag) > data_end) {
+ return XDP_DROP;
+ }
+ ip_proto = frag->nexthdr;
+ data += sizeof(*frag);
+ }
+ l4_hdr = data;
+ ipv4 = 0;
+ break;
+ default:
+ /* Pass packets of possible other protocols. */
+ return XDP_PASS;
+ }
+
+ const struct tcphdr *tcp;
+ const struct udphdr *udp;
+ __u16 port_dest;
+ __u8 match = 0;
+
+ /* Check the transport protocol. */
+ switch (ip_proto) {
+ case IPPROTO_TCP:
+ /* Parse TCP header. */
+ tcp = l4_hdr;
+ if (l4_hdr + sizeof(*tcp) > data_end) {
+ return XDP_DROP;
+ }
+
+ port_dest = __bpf_ntohs(tcp->dest);
+
+ if ((opts.flags & KNOT_XDP_FILTER_TCP) &&
+ (port_dest == opts.udp_port ||
+ ((opts.flags & (KNOT_XDP_FILTER_PASS | KNOT_XDP_FILTER_DROP)) &&
+ port_dest >= opts.udp_port))) {
+ match = 1;
+ }
+ break;
+ case IPPROTO_UDP:
+ /* Parse UDP header. */
+ udp = l4_hdr;
+ if (l4_hdr + sizeof(*udp) > data_end) {
+ return XDP_DROP;
+ }
+
+ /* Check the UDP length. */
+ if (data_end - (void *)udp < __bpf_ntohs(udp->len)) {
+ return XDP_DROP;
+ }
+
+ port_dest = __bpf_ntohs(udp->dest);
+
+ if ((opts.flags & KNOT_XDP_FILTER_UDP) &&
+ (port_dest == opts.udp_port ||
+ ((opts.flags & (KNOT_XDP_FILTER_PASS | KNOT_XDP_FILTER_DROP)) &&
+ port_dest >= opts.udp_port))) {
+ match = 1;
+ } else if ((opts.flags & KNOT_XDP_FILTER_QUIC) &&
+ (port_dest == opts.quic_port ||
+ ((opts.flags & (KNOT_XDP_FILTER_PASS | KNOT_XDP_FILTER_DROP)) &&
+ port_dest >= opts.quic_port))) {
+ match = 1;
+ }
+ break;
+ default:
+ /* Pass packets of possible other protocols. */
+ return XDP_PASS;
+ }
+
+ if (!match) {
+ /* Pass non-matching packet. */
+ return XDP_PASS;
+ } else if (opts.flags & KNOT_XDP_FILTER_DROP) {
+ /* Drop matching packet if requested. */
+ return XDP_DROP;
+ } else if (fragmented) {
+ /* Drop fragmented packet. */
+ return XDP_DROP;
+ }
+
+ /* Take into account routing information. */
+ if (opts.flags & KNOT_XDP_FILTER_ROUTE) {
+ struct bpf_fib_lookup fib = {
+ .ifindex = 1 /* Loopback. */
+ };
+ if (ipv4) {
+ fib.family = AF_INET;
+ fib.ipv4_src = ip4->daddr;
+ fib.ipv4_dst = ip4->saddr;
+ } else {
+ struct in6_addr *ipv6_src = (struct in6_addr *)fib.ipv6_src;
+ struct in6_addr *ipv6_dst = (struct in6_addr *)fib.ipv6_dst;
+ fib.family = AF_INET6;
+ *ipv6_src = ip6->daddr;
+ *ipv6_dst = ip6->saddr;
+ }
+
+ const __u16 *mac_in = (const __u16 *)eth_hdr->h_dest;
+ const __u16 *mac_out = (const __u16 *)fib.smac;
+ int ret = bpf_fib_lookup(ctx, &fib, sizeof(fib), BPF_FIB_LOOKUP_DIRECT);
+ switch (ret) {
+ case BPF_FIB_LKUP_RET_SUCCESS:
+ /* Cross-interface answers are handled through normal stack. */
+ if (mac_in[0] != mac_out[0] ||
+ mac_in[1] != mac_out[1] ||
+ mac_in[2] != mac_out[2]) {
+ return XDP_PASS;
+ }
+
+ /* Store output interface index for later use with VLAN in user space. */
+ if (meta != 0) {
+ meta->out_if_index = fib.ifindex;
+ }
+
+ /* Update destination MAC for responding. */
+ __builtin_memcpy(eth_hdr->h_source, fib.dmac, ETH_ALEN);
+ break;
+ case BPF_FIB_LKUP_RET_FWD_DISABLED: /* Disabled forwarding on loopback. */
+ return XDP_ABORTED;
+ case BPF_FIB_LKUP_RET_NO_NEIGH: /* Use normal stack to obtain MAC. */
+ return XDP_PASS;
+ default:
+ return XDP_DROP;
+ }
+ }
+
+ /* Forward the packet to user space. */
+ return bpf_redirect_map(&xsks_map, ctx->rx_queue_index, 0);
+}
+
+char _license[] SEC("license") = "GPL";
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