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