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