/* SPDX-License-Identifier: GPL-2.0 * Copyright(c) 2018 Jesper Dangaard Brouer. * * XDP/TC VLAN manipulation example * * GOTCHA: Remember to disable NIC hardware offloading of VLANs, * else the VLAN tags are NOT inlined in the packet payload: * * # ethtool -K ixgbe2 rxvlan off * * Verify setting: * # ethtool -k ixgbe2 | grep rx-vlan-offload * rx-vlan-offload: off * */ #include #include #include #include #include #include #include #include #include #include /* linux/if_vlan.h have not exposed this as UAPI, thus mirror some here * * struct vlan_hdr - vlan header * @h_vlan_TCI: priority and VLAN ID * @h_vlan_encapsulated_proto: packet type ID or len */ struct _vlan_hdr { __be16 h_vlan_TCI; __be16 h_vlan_encapsulated_proto; }; #define VLAN_PRIO_MASK 0xe000 /* Priority Code Point */ #define VLAN_PRIO_SHIFT 13 #define VLAN_CFI_MASK 0x1000 /* Canonical Format Indicator */ #define VLAN_TAG_PRESENT VLAN_CFI_MASK #define VLAN_VID_MASK 0x0fff /* VLAN Identifier */ #define VLAN_N_VID 4096 struct parse_pkt { __u16 l3_proto; __u16 l3_offset; __u16 vlan_outer; __u16 vlan_inner; __u8 vlan_outer_offset; __u8 vlan_inner_offset; }; char _license[] SEC("license") = "GPL"; static __always_inline bool parse_eth_frame(struct ethhdr *eth, void *data_end, struct parse_pkt *pkt) { __u16 eth_type; __u8 offset; offset = sizeof(*eth); /* Make sure packet is large enough for parsing eth + 2 VLAN headers */ if ((void *)eth + offset + (2*sizeof(struct _vlan_hdr)) > data_end) return false; eth_type = eth->h_proto; /* Handle outer VLAN tag */ if (eth_type == bpf_htons(ETH_P_8021Q) || eth_type == bpf_htons(ETH_P_8021AD)) { struct _vlan_hdr *vlan_hdr; vlan_hdr = (void *)eth + offset; pkt->vlan_outer_offset = offset; pkt->vlan_outer = bpf_ntohs(vlan_hdr->h_vlan_TCI) & VLAN_VID_MASK; eth_type = vlan_hdr->h_vlan_encapsulated_proto; offset += sizeof(*vlan_hdr); } /* Handle inner (double) VLAN tag */ if (eth_type == bpf_htons(ETH_P_8021Q) || eth_type == bpf_htons(ETH_P_8021AD)) { struct _vlan_hdr *vlan_hdr; vlan_hdr = (void *)eth + offset; pkt->vlan_inner_offset = offset; pkt->vlan_inner = bpf_ntohs(vlan_hdr->h_vlan_TCI) & VLAN_VID_MASK; eth_type = vlan_hdr->h_vlan_encapsulated_proto; offset += sizeof(*vlan_hdr); } pkt->l3_proto = bpf_ntohs(eth_type); /* Convert to host-byte-order */ pkt->l3_offset = offset; return true; } /* Hint, VLANs are chosen to hit network-byte-order issues */ #define TESTVLAN 4011 /* 0xFAB */ // #define TO_VLAN 4000 /* 0xFA0 (hint 0xOA0 = 160) */ SEC("xdp_drop_vlan_4011") int xdp_prognum0(struct xdp_md *ctx) { void *data_end = (void *)(long)ctx->data_end; void *data = (void *)(long)ctx->data; struct parse_pkt pkt = { 0 }; if (!parse_eth_frame(data, data_end, &pkt)) return XDP_ABORTED; /* Drop specific VLAN ID example */ if (pkt.vlan_outer == TESTVLAN) return XDP_ABORTED; /* * Using XDP_ABORTED makes it possible to record this event, * via tracepoint xdp:xdp_exception like: * # perf record -a -e xdp:xdp_exception * # perf script */ return XDP_PASS; } /* Commands to setup VLAN on Linux to test packets gets dropped: export ROOTDEV=ixgbe2 export VLANID=4011 ip link add link $ROOTDEV name $ROOTDEV.$VLANID type vlan id $VLANID ip link set dev $ROOTDEV.$VLANID up ip link set dev $ROOTDEV mtu 1508 ip addr add 100.64.40.11/24 dev $ROOTDEV.$VLANID Load prog with ip tool: ip link set $ROOTDEV xdp off ip link set $ROOTDEV xdp object xdp_vlan01_kern.o section xdp_drop_vlan_4011 */ /* Changing VLAN to zero, have same practical effect as removing the VLAN. */ #define TO_VLAN 0 SEC("xdp_vlan_change") int xdp_prognum1(struct xdp_md *ctx) { void *data_end = (void *)(long)ctx->data_end; void *data = (void *)(long)ctx->data; struct parse_pkt pkt = { 0 }; if (!parse_eth_frame(data, data_end, &pkt)) return XDP_ABORTED; /* Change specific VLAN ID */ if (pkt.vlan_outer == TESTVLAN) { struct _vlan_hdr *vlan_hdr = data + pkt.vlan_outer_offset; /* Modifying VLAN, preserve top 4 bits */ vlan_hdr->h_vlan_TCI = bpf_htons((bpf_ntohs(vlan_hdr->h_vlan_TCI) & 0xf000) | TO_VLAN); } return XDP_PASS; } /* * Show XDP+TC can cooperate, on creating a VLAN rewriter. * 1. Create a XDP prog that can "pop"/remove a VLAN header. * 2. Create a TC-bpf prog that egress can add a VLAN header. */ #ifndef ETH_ALEN /* Ethernet MAC address length */ #define ETH_ALEN 6 /* bytes */ #endif #define VLAN_HDR_SZ 4 /* bytes */ SEC("xdp_vlan_remove_outer") int xdp_prognum2(struct xdp_md *ctx) { void *data_end = (void *)(long)ctx->data_end; void *data = (void *)(long)ctx->data; struct parse_pkt pkt = { 0 }; char *dest; if (!parse_eth_frame(data, data_end, &pkt)) return XDP_ABORTED; /* Skip packet if no outer VLAN was detected */ if (pkt.vlan_outer_offset == 0) return XDP_PASS; /* Moving Ethernet header, dest overlap with src, memmove handle this */ dest = data; dest += VLAN_HDR_SZ; /* * Notice: Taking over vlan_hdr->h_vlan_encapsulated_proto, by * only moving two MAC addrs (12 bytes), not overwriting last 2 bytes */ __builtin_memmove(dest, data, ETH_ALEN * 2); /* Note: LLVM built-in memmove inlining require size to be constant */ /* Move start of packet header seen by Linux kernel stack */ bpf_xdp_adjust_head(ctx, VLAN_HDR_SZ); return XDP_PASS; } static __always_inline void shift_mac_4bytes_32bit(void *data) { __u32 *p = data; /* Assuming VLAN hdr present. The 4 bytes in p[3] that gets * overwritten, is ethhdr->h_proto and vlan_hdr->h_vlan_TCI. * The vlan_hdr->h_vlan_encapsulated_proto take over role as * ethhdr->h_proto. */ p[3] = p[2]; p[2] = p[1]; p[1] = p[0]; } SEC("xdp_vlan_remove_outer2") int xdp_prognum3(struct xdp_md *ctx) { void *data_end = (void *)(long)ctx->data_end; void *data = (void *)(long)ctx->data; struct ethhdr *orig_eth = data; struct parse_pkt pkt = { 0 }; if (!parse_eth_frame(orig_eth, data_end, &pkt)) return XDP_ABORTED; /* Skip packet if no outer VLAN was detected */ if (pkt.vlan_outer_offset == 0) return XDP_PASS; /* Simply shift down MAC addrs 4 bytes, overwrite h_proto + TCI */ shift_mac_4bytes_32bit(data); /* Move start of packet header seen by Linux kernel stack */ bpf_xdp_adjust_head(ctx, VLAN_HDR_SZ); return XDP_PASS; } /*===================================== * BELOW: TC-hook based ebpf programs * ==================================== * The TC-clsact eBPF programs (currently) need to be attach via TC commands */ SEC("tc_vlan_push") int _tc_progA(struct __sk_buff *ctx) { bpf_skb_vlan_push(ctx, bpf_htons(ETH_P_8021Q), TESTVLAN); return TC_ACT_OK; } /* Commands to setup TC to use above bpf prog: export ROOTDEV=ixgbe2 export FILE=xdp_vlan01_kern.o # Re-attach clsact to clear/flush existing role tc qdisc del dev $ROOTDEV clsact 2> /dev/null ;\ tc qdisc add dev $ROOTDEV clsact # Attach BPF prog EGRESS tc filter add dev $ROOTDEV egress \ prio 1 handle 1 bpf da obj $FILE sec tc_vlan_push tc filter show dev $ROOTDEV egress */