1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (c) 2017 Facebook
3 */
4#include <stddef.h>
5#include <string.h>
6#include <linux/bpf.h>
7#include <linux/if_ether.h>
8#include <linux/if_packet.h>
9#include <linux/ip.h>
10#include <linux/ipv6.h>
11#include <linux/in.h>
12#include <linux/tcp.h>
13#include <linux/pkt_cls.h>
14#include <bpf/bpf_helpers.h>
15#include <bpf/bpf_endian.h>
16#include "bpf_misc.h"
17
18/* llvm will optimize both subprograms into exactly the same BPF assembly
19 *
20 * Disassembly of section .text:
21 *
22 * 0000000000000000 test_pkt_access_subprog1:
23 * ; 	return skb->len * 2;
24 *        0:	61 10 00 00 00 00 00 00	r0 = *(u32 *)(r1 + 0)
25 *        1:	64 00 00 00 01 00 00 00	w0 <<= 1
26 *        2:	95 00 00 00 00 00 00 00	exit
27 *
28 * 0000000000000018 test_pkt_access_subprog2:
29 * ; 	return skb->len * val;
30 *        3:	61 10 00 00 00 00 00 00	r0 = *(u32 *)(r1 + 0)
31 *        4:	64 00 00 00 01 00 00 00	w0 <<= 1
32 *        5:	95 00 00 00 00 00 00 00	exit
33 *
34 * Which makes it an interesting test for BTF-enabled verifier.
35 */
36static __attribute__ ((noinline))
37int test_pkt_access_subprog1(volatile struct __sk_buff *skb)
38{
39	return skb->len * 2;
40}
41
42static __attribute__ ((noinline))
43int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
44{
45	return skb->len * val;
46}
47
48#define MAX_STACK (512 - 2 * 32)
49
50__attribute__ ((noinline))
51int get_skb_len(struct __sk_buff *skb)
52{
53	volatile char buf[MAX_STACK] = {};
54
55	__sink(buf[MAX_STACK - 1]);
56
57	return skb->len;
58}
59
60__attribute__ ((noinline))
61int get_constant(long val)
62{
63	return val - 122;
64}
65
66int get_skb_ifindex(int, struct __sk_buff *skb, int);
67
68__attribute__ ((noinline))
69int test_pkt_access_subprog3(int val, struct __sk_buff *skb)
70{
71	return get_skb_len(skb) * get_skb_ifindex(val, skb, get_constant(123));
72}
73
74__attribute__ ((noinline))
75int get_skb_ifindex(int val, struct __sk_buff *skb, int var)
76{
77	volatile char buf[MAX_STACK] = {};
78
79	__sink(buf[MAX_STACK - 1]);
80
81	return skb->ifindex * val * var;
82}
83
84__attribute__ ((noinline))
85int test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
86{
87	void *data = (void *)(long)skb->data;
88	void *data_end = (void *)(long)skb->data_end;
89	struct tcphdr *tcp = NULL;
90
91	if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
92		return -1;
93
94	tcp = data + off;
95	if (tcp + 1 > data_end)
96		return -1;
97	/* make modification to the packet data */
98	tcp->check++;
99	return 0;
100}
101
102SEC("tc")
103int test_pkt_access(struct __sk_buff *skb)
104{
105	void *data_end = (void *)(long)skb->data_end;
106	void *data = (void *)(long)skb->data;
107	struct ethhdr *eth = (struct ethhdr *)(data);
108	struct tcphdr *tcp = NULL;
109	__u8 proto = 255;
110	__u64 ihl_len;
111
112	if (eth + 1 > data_end)
113		return TC_ACT_SHOT;
114
115	if (eth->h_proto == bpf_htons(ETH_P_IP)) {
116		struct iphdr *iph = (struct iphdr *)(eth + 1);
117
118		if (iph + 1 > data_end)
119			return TC_ACT_SHOT;
120		ihl_len = iph->ihl * 4;
121		proto = iph->protocol;
122		tcp = (struct tcphdr *)((void *)(iph) + ihl_len);
123	} else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
124		struct ipv6hdr *ip6h = (struct ipv6hdr *)(eth + 1);
125
126		if (ip6h + 1 > data_end)
127			return TC_ACT_SHOT;
128		ihl_len = sizeof(*ip6h);
129		proto = ip6h->nexthdr;
130		tcp = (struct tcphdr *)((void *)(ip6h) + ihl_len);
131	}
132
133	if (test_pkt_access_subprog1(skb) != skb->len * 2)
134		return TC_ACT_SHOT;
135	if (test_pkt_access_subprog2(2, skb) != skb->len * 2)
136		return TC_ACT_SHOT;
137	if (test_pkt_access_subprog3(3, skb) != skb->len * 3 * skb->ifindex)
138		return TC_ACT_SHOT;
139	if (tcp) {
140		if (test_pkt_write_access_subprog(skb, (void *)tcp - data))
141			return TC_ACT_SHOT;
142		if (((void *)(tcp) + 20) > data_end || proto != 6)
143			return TC_ACT_SHOT;
144		barrier(); /* to force ordering of checks */
145		if (((void *)(tcp) + 18) > data_end)
146			return TC_ACT_SHOT;
147		if (tcp->urg_ptr == 123)
148			return TC_ACT_OK;
149	}
150
151	return TC_ACT_UNSPEC;
152}
153