/* 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 <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/in.h>
#include <linux/pkt_cls.h>

#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

/* 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")
int xdp_drop_vlan_4011(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")
int xdp_vlan_change(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) & 0xf000U)
                                  | 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")
int xdp_vlan_remove_outer(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")
int xdp_vlan_remove_outer2(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")
int tc_vlan_push(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
*/