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  */
36 static __attribute__ ((noinline))
37 int test_pkt_access_subprog1(volatile struct __sk_buff *skb)
38 {
39 	return skb->len * 2;
40 }
41 
42 static __attribute__ ((noinline))
43 int 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))
51 int 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))
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 	__sink(buf[MAX_STACK - 1]);
80 
81 	return skb->ifindex * val * var;
82 }
83 
84 __attribute__ ((noinline))
85 int 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 
102 SEC("tc")
103 int 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