// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved. */

#define KBUILD_MODNAME "foo"
#include <stddef.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/icmp.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/if_vlan.h>
#include <linux/ip.h>

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

#include "bpf_compiler.h"
#include "xdping.h"

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(max_entries, 256);
        __type(key, __u32);
        __type(value, struct pinginfo);
} ping_map SEC(".maps");

static __always_inline void swap_src_dst_mac(void *data)
{
        unsigned short *p = data;
        unsigned short dst[3];

        dst[0] = p[0];
        dst[1] = p[1];
        dst[2] = p[2];
        p[0] = p[3];
        p[1] = p[4];
        p[2] = p[5];
        p[3] = dst[0];
        p[4] = dst[1];
        p[5] = dst[2];
}

static __always_inline __u16 csum_fold_helper(__wsum sum)
{
        sum = (sum & 0xffff) + (sum >> 16);
        return ~((sum & 0xffff) + (sum >> 16));
}

static __always_inline __u16 ipv4_csum(void *data_start, int data_size)
{
        __wsum sum;

        sum = bpf_csum_diff(0, 0, data_start, data_size, 0);
        return csum_fold_helper(sum);
}

#define ICMP_ECHO_LEN           64

static __always_inline int icmp_check(struct xdp_md *ctx, int type)
{
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        struct ethhdr *eth = data;
        struct icmphdr *icmph;
        struct iphdr *iph;

        if (data + sizeof(*eth) + sizeof(*iph) + ICMP_ECHO_LEN > data_end)
                return XDP_PASS;

        if (eth->h_proto != bpf_htons(ETH_P_IP))
                return XDP_PASS;

        iph = data + sizeof(*eth);

        if (iph->protocol != IPPROTO_ICMP)
                return XDP_PASS;

        if (bpf_ntohs(iph->tot_len) - sizeof(*iph) != ICMP_ECHO_LEN)
                return XDP_PASS;

        icmph = data + sizeof(*eth) + sizeof(*iph);

        if (icmph->type != type)
                return XDP_PASS;

        return XDP_TX;
}

SEC("xdp")
int xdping_client(struct xdp_md *ctx)
{
        void *data = (void *)(long)ctx->data;
        struct pinginfo *pinginfo = NULL;
        struct ethhdr *eth = data;
        struct icmphdr *icmph;
        struct iphdr *iph;
        __u64 recvtime;
        __be32 raddr;
        __be16 seq;
        int ret;
        __u8 i;

        ret = icmp_check(ctx, ICMP_ECHOREPLY);

        if (ret != XDP_TX)
                return ret;

        iph = data + sizeof(*eth);
        icmph = data + sizeof(*eth) + sizeof(*iph);
        raddr = iph->saddr;

        /* Record time reply received. */
        recvtime = bpf_ktime_get_ns();
        pinginfo = bpf_map_lookup_elem(&ping_map, &raddr);
        if (!pinginfo || pinginfo->seq != icmph->un.echo.sequence)
                return XDP_PASS;

        if (pinginfo->start) {
                __pragma_loop_unroll_full
                for (i = 0; i < XDPING_MAX_COUNT; i++) {
                        if (pinginfo->times[i] == 0)
                                break;
                }
                /* verifier is fussy here... */
                if (i < XDPING_MAX_COUNT) {
                        pinginfo->times[i] = recvtime -
                                             pinginfo->start;
                        pinginfo->start = 0;
                        i++;
                }
                /* No more space for values? */
                if (i == pinginfo->count || i == XDPING_MAX_COUNT)
                        return XDP_PASS;
        }

        /* Now convert reply back into echo request. */
        swap_src_dst_mac(data);
        iph->saddr = iph->daddr;
        iph->daddr = raddr;
        icmph->type = ICMP_ECHO;
        seq = bpf_htons(bpf_ntohs(icmph->un.echo.sequence) + 1);
        icmph->un.echo.sequence = seq;
        icmph->checksum = 0;
        icmph->checksum = ipv4_csum(icmph, ICMP_ECHO_LEN);

        pinginfo->seq = seq;
        pinginfo->start = bpf_ktime_get_ns();

        return XDP_TX;
}

SEC("xdp")
int xdping_server(struct xdp_md *ctx)
{
        void *data = (void *)(long)ctx->data;
        struct ethhdr *eth = data;
        struct icmphdr *icmph;
        struct iphdr *iph;
        __be32 raddr;
        int ret;

        ret = icmp_check(ctx, ICMP_ECHO);

        if (ret != XDP_TX)
                return ret;

        iph = data + sizeof(*eth);
        icmph = data + sizeof(*eth) + sizeof(*iph);
        raddr = iph->saddr;

        /* Now convert request into echo reply. */
        swap_src_dst_mac(data);
        iph->saddr = iph->daddr;
        iph->daddr = raddr;
        icmph->type = ICMP_ECHOREPLY;
        icmph->checksum = 0;
        icmph->checksum = ipv4_csum(icmph, ICMP_ECHO_LEN);

        return XDP_TX;
}

char _license[] SEC("license") = "GPL";