1// SPDX-License-Identifier: GPL-2.0
2/* Copyright (c) 2019 Facebook */
3#include <linux/stddef.h>
4#include <linux/if_ether.h>
5#include <linux/ipv6.h>
6#include <linux/bpf.h>
7#include <linux/tcp.h>
8#include <bpf/bpf_helpers.h>
9#include <bpf/bpf_endian.h>
10#include <bpf/bpf_tracing.h>
11
12struct sk_buff {
13	unsigned int len;
14};
15
16__u64 test_result = 0;
17SEC("fexit/test_pkt_access")
18int BPF_PROG(test_main, struct sk_buff *skb, int ret)
19{
20	int len;
21
22	__builtin_preserve_access_index(({
23		len = skb->len;
24	}));
25	if (len != 74 || ret != 0)
26		return 0;
27	test_result = 1;
28	return 0;
29}
30
31__u64 test_result_subprog1 = 0;
32SEC("fexit/test_pkt_access_subprog1")
33int BPF_PROG(test_subprog1, struct sk_buff *skb, int ret)
34{
35	int len;
36
37	__builtin_preserve_access_index(({
38		len = skb->len;
39	}));
40	if (len != 74 || ret != 148)
41		return 0;
42	test_result_subprog1 = 1;
43	return 0;
44}
45
46/* Though test_pkt_access_subprog2() is defined in C as:
47 * static __attribute__ ((noinline))
48 * int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
49 * {
50 *     return skb->len * val;
51 * }
52 * llvm optimizations remove 'int val' argument and generate BPF assembly:
53 *   r0 = *(u32 *)(r1 + 0)
54 *   w0 <<= 1
55 *   exit
56 * In such case the verifier falls back to conservative and
57 * tracing program can access arguments and return value as u64
58 * instead of accurate types.
59 */
60struct args_subprog2 {
61	__u64 args[5];
62	__u64 ret;
63};
64__u64 test_result_subprog2 = 0;
65SEC("fexit/test_pkt_access_subprog2")
66int test_subprog2(struct args_subprog2 *ctx)
67{
68	struct sk_buff *skb = (void *)ctx->args[0];
69	__u64 ret;
70	int len;
71
72	bpf_probe_read_kernel(&len, sizeof(len),
73			      __builtin_preserve_access_index(&skb->len));
74
75	ret = ctx->ret;
76	/* bpf_prog_test_load() loads "test_pkt_access.bpf.o" with
77	 * BPF_F_TEST_RND_HI32 which randomizes upper 32 bits after BPF_ALU32
78	 * insns. Hence after 'w0 <<= 1' upper bits of $rax are random. That is
79	 * expected and correct. Trim them.
80	 */
81	ret = (__u32) ret;
82	if (len != 74 || ret != 148)
83		return 0;
84	test_result_subprog2 = 1;
85	return 0;
86}
87
88__u64 test_result_subprog3 = 0;
89SEC("fexit/test_pkt_access_subprog3")
90int BPF_PROG(test_subprog3, int val, struct sk_buff *skb, int ret)
91{
92	int len;
93
94	__builtin_preserve_access_index(({
95		len = skb->len;
96	}));
97	if (len != 74 || ret != 74 * val || val != 3)
98		return 0;
99	test_result_subprog3 = 1;
100	return 0;
101}
102
103__u64 test_get_skb_len = 0;
104SEC("freplace/get_skb_len")
105int new_get_skb_len(struct __sk_buff *skb)
106{
107	int len = skb->len;
108
109	if (len != 74)
110		return 0;
111	test_get_skb_len = 1;
112	return 74; /* original get_skb_len() returns skb->len */
113}
114
115__u64 test_get_skb_ifindex = 0;
116SEC("freplace/get_skb_ifindex")
117int new_get_skb_ifindex(int val, struct __sk_buff *skb, int var)
118{
119	void *data_end = (void *)(long)skb->data_end;
120	void *data = (void *)(long)skb->data;
121	struct ipv6hdr ip6, *ip6p;
122	int ifindex = skb->ifindex;
123
124	/* check that BPF extension can read packet via direct packet access */
125	if (data + 14 + sizeof(ip6) > data_end)
126		return 0;
127	ip6p = data + 14;
128
129	if (ip6p->nexthdr != 6 || ip6p->payload_len != __bpf_constant_htons(123))
130		return 0;
131
132	/* check that legacy packet access helper works too */
133	if (bpf_skb_load_bytes(skb, 14, &ip6, sizeof(ip6)) < 0)
134		return 0;
135	ip6p = &ip6;
136	if (ip6p->nexthdr != 6 || ip6p->payload_len != __bpf_constant_htons(123))
137		return 0;
138
139	if (ifindex != 1 || val != 3 || var != 1)
140		return 0;
141	test_get_skb_ifindex = 1;
142	return 3; /* original get_skb_ifindex() returns val * ifindex * var */
143}
144
145volatile __u64 test_get_constant = 0;
146SEC("freplace/get_constant")
147int new_get_constant(long val)
148{
149	if (val != 123)
150		return 0;
151	test_get_constant = 1;
152	return test_get_constant; /* original get_constant() returns val - 122 */
153}
154
155__u64 test_pkt_write_access_subprog = 0;
156SEC("freplace/test_pkt_write_access_subprog")
157int new_test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
158{
159
160	void *data = (void *)(long)skb->data;
161	void *data_end = (void *)(long)skb->data_end;
162	struct tcphdr *tcp;
163
164	if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
165		return -1;
166
167	tcp = data + off;
168	if (tcp + 1 > data_end)
169		return -1;
170
171	/* make modifications to the packet data */
172	tcp->check++;
173	tcp->syn = 0;
174
175	test_pkt_write_access_subprog = 1;
176	return 0;
177}
178
179char _license[] SEC("license") = "GPL";
180