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))
test_pkt_access_subprog1(volatile struct __sk_buff * skb)39 int test_pkt_access_subprog1(volatile struct __sk_buff *skb)
40 {
41 return skb->len * 2;
42 }
43
44 static __attribute__ ((noinline))
test_pkt_access_subprog2(int val,volatile struct __sk_buff * skb)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))
get_skb_len(struct __sk_buff * skb)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))
get_constant(long val)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))
test_pkt_access_subprog3(int val,struct __sk_buff * skb)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))
get_skb_ifindex(int val,struct __sk_buff * skb,int var)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))
test_pkt_write_access_subprog(struct __sk_buff * skb,__u32 off)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")
test_pkt_access(struct __sk_buff * skb)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