// 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_load() loads "test_pkt_access.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;
	__u32 eth_proto;
	__u32 nh_off;

	/* 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";