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