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))
test_pkt_access_subprog1(volatile struct __sk_buff * skb)38 int test_pkt_access_subprog1(volatile struct __sk_buff *skb)
39 {
40 return skb->len * 2;
41 }
42
43 static __attribute__ ((noinline))
test_pkt_access_subprog2(int val,volatile struct __sk_buff * skb)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))
get_skb_len(struct __sk_buff * skb)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))
get_constant(long val)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))
test_pkt_access_subprog3(int val,struct __sk_buff * skb)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))
get_skb_ifindex(int val,struct __sk_buff * skb,int var)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))
test_pkt_write_access_subprog(struct __sk_buff * skb,__u32 off)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")
test_pkt_access(struct __sk_buff * skb)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