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
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