// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook */
#include <linux/stddef.h>
#include <linux/if_ether.h>
#include <linux/ipv6.h>
#include <linux/bpf.h>
#include <linux/tcp.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_tracing.h>

struct sk_buff {
        unsigned int len;
};

__u64 test_result = 0;
SEC("fexit/test_pkt_access")
int BPF_PROG(test_main, struct sk_buff *skb, int ret)
{
        int len;

        __builtin_preserve_access_index(({
                len = skb->len;
        }));
        if (len != 74 || ret != 0)
                return 0;
        test_result = 1;
        return 0;
}

__u64 test_result_subprog1 = 0;
SEC("fexit/test_pkt_access_subprog1")
int BPF_PROG(test_subprog1, struct sk_buff *skb, int ret)
{
        int len;

        __builtin_preserve_access_index(({
                len = skb->len;
        }));
        if (len != 74 || ret != 148)
                return 0;
        test_result_subprog1 = 1;
        return 0;
}

/* Though test_pkt_access_subprog2() is defined in C as:
 * static __attribute__ ((noinline))
 * int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
 * {
 *     return skb->len * val;
 * }
 * llvm optimizations remove 'int val' argument and generate BPF assembly:
 *   r0 = *(u32 *)(r1 + 0)
 *   w0 <<= 1
 *   exit
 * In such case the verifier falls back to conservative and
 * tracing program can access arguments and return value as u64
 * instead of accurate types.
 */
struct args_subprog2 {
        __u64 args[5];
        __u64 ret;
};
__u64 test_result_subprog2 = 0;
SEC("fexit/test_pkt_access_subprog2")
int test_subprog2(struct args_subprog2 *ctx)
{
        struct sk_buff *skb = (void *)ctx->args[0];
        __u64 ret;
        int len;

        bpf_probe_read_kernel(&len, sizeof(len),
                              __builtin_preserve_access_index(&skb->len));

        ret = ctx->ret;
        /* bpf_prog_test_load() loads "test_pkt_access.bpf.o" with
         * BPF_F_TEST_RND_HI32 which randomizes upper 32 bits after BPF_ALU32
         * insns. Hence after 'w0 <<= 1' upper bits of $rax are random. That is
         * expected and correct. Trim them.
         */
        ret = (__u32) ret;
        if (len != 74 || ret != 148)
                return 0;
        test_result_subprog2 = 1;
        return 0;
}

__u64 test_result_subprog3 = 0;
SEC("fexit/test_pkt_access_subprog3")
int BPF_PROG(test_subprog3, int val, struct sk_buff *skb, int ret)
{
        int len;

        __builtin_preserve_access_index(({
                len = skb->len;
        }));
        if (len != 74 || ret != 74 * val || val != 3)
                return 0;
        test_result_subprog3 = 1;
        return 0;
}

__u64 test_get_skb_len = 0;
SEC("freplace/get_skb_len")
int new_get_skb_len(struct __sk_buff *skb)
{
        int len = skb->len;

        if (len != 74)
                return 0;
        test_get_skb_len = 1;
        return 74; /* original get_skb_len() returns skb->len */
}

__u64 test_get_skb_ifindex = 0;
SEC("freplace/get_skb_ifindex")
int new_get_skb_ifindex(int val, struct __sk_buff *skb, int var)
{
        void *data_end = (void *)(long)skb->data_end;
        void *data = (void *)(long)skb->data;
        struct ipv6hdr ip6, *ip6p;
        int ifindex = skb->ifindex;

        /* check that BPF extension can read packet via direct packet access */
        if (data + 14 + sizeof(ip6) > data_end)
                return 0;
        ip6p = data + 14;

        if (ip6p->nexthdr != 6 || ip6p->payload_len != __bpf_constant_htons(123))
                return 0;

        /* check that legacy packet access helper works too */
        if (bpf_skb_load_bytes(skb, 14, &ip6, sizeof(ip6)) < 0)
                return 0;
        ip6p = &ip6;
        if (ip6p->nexthdr != 6 || ip6p->payload_len != __bpf_constant_htons(123))
                return 0;

        if (ifindex != 1 || val != 3 || var != 1)
                return 0;
        test_get_skb_ifindex = 1;
        return 3; /* original get_skb_ifindex() returns val * ifindex * var */
}

volatile __u64 test_get_constant = 0;
SEC("freplace/get_constant")
int new_get_constant(long val)
{
        if (val != 123)
                return 0;
        test_get_constant = 1;
        return test_get_constant; /* original get_constant() returns val - 122 */
}

__u64 test_pkt_write_access_subprog = 0;
SEC("freplace/test_pkt_write_access_subprog")
int new_test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
{

        void *data = (void *)(long)skb->data;
        void *data_end = (void *)(long)skb->data_end;
        struct tcphdr *tcp;

        if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
                return -1;

        tcp = data + off;
        if (tcp + 1 > data_end)
                return -1;

        /* make modifications to the packet data */
        tcp->check++;
        tcp->syn = 0;

        test_pkt_write_access_subprog = 1;
        return 0;
}

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