1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
|
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2017 Facebook
*/
#include <stddef.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <linux/pkt_cls.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
/* llvm will optimize both subprograms into exactly the same BPF assembly
*
* Disassembly of section .text:
*
* 0000000000000000 test_pkt_access_subprog1:
* ; return skb->len * 2;
* 0: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0)
* 1: 64 00 00 00 01 00 00 00 w0 <<= 1
* 2: 95 00 00 00 00 00 00 00 exit
*
* 0000000000000018 test_pkt_access_subprog2:
* ; return skb->len * val;
* 3: 61 10 00 00 00 00 00 00 r0 = *(u32 *)(r1 + 0)
* 4: 64 00 00 00 01 00 00 00 w0 <<= 1
* 5: 95 00 00 00 00 00 00 00 exit
*
* Which makes it an interesting test for BTF-enabled verifier.
*/
static __attribute__ ((noinline))
int test_pkt_access_subprog1(volatile struct __sk_buff *skb)
{
return skb->len * 2;
}
static __attribute__ ((noinline))
int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
{
return skb->len * val;
}
#define MAX_STACK (512 - 2 * 32)
__attribute__ ((noinline))
int get_skb_len(struct __sk_buff *skb)
{
volatile char buf[MAX_STACK] = {};
return skb->len;
}
__attribute__ ((noinline))
int get_constant(long val)
{
return val - 122;
}
int get_skb_ifindex(int, struct __sk_buff *skb, int);
__attribute__ ((noinline))
int test_pkt_access_subprog3(int val, struct __sk_buff *skb)
{
return get_skb_len(skb) * get_skb_ifindex(val, skb, get_constant(123));
}
__attribute__ ((noinline))
int get_skb_ifindex(int val, struct __sk_buff *skb, int var)
{
volatile char buf[MAX_STACK] = {};
return skb->ifindex * val * var;
}
__attribute__ ((noinline))
int test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
{
void *data = (void *)(long)skb->data;
void *data_end = (void *)(long)skb->data_end;
struct tcphdr *tcp = NULL;
if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
return -1;
tcp = data + off;
if (tcp + 1 > data_end)
return -1;
/* make modification to the packet data */
tcp->check++;
return 0;
}
SEC("tc")
int test_pkt_access(struct __sk_buff *skb)
{
void *data_end = (void *)(long)skb->data_end;
void *data = (void *)(long)skb->data;
struct ethhdr *eth = (struct ethhdr *)(data);
struct tcphdr *tcp = NULL;
__u8 proto = 255;
__u64 ihl_len;
if (eth + 1 > data_end)
return TC_ACT_SHOT;
if (eth->h_proto == bpf_htons(ETH_P_IP)) {
struct iphdr *iph = (struct iphdr *)(eth + 1);
if (iph + 1 > data_end)
return TC_ACT_SHOT;
ihl_len = iph->ihl * 4;
proto = iph->protocol;
tcp = (struct tcphdr *)((void *)(iph) + ihl_len);
} else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
struct ipv6hdr *ip6h = (struct ipv6hdr *)(eth + 1);
if (ip6h + 1 > data_end)
return TC_ACT_SHOT;
ihl_len = sizeof(*ip6h);
proto = ip6h->nexthdr;
tcp = (struct tcphdr *)((void *)(ip6h) + ihl_len);
}
if (test_pkt_access_subprog1(skb) != skb->len * 2)
return TC_ACT_SHOT;
if (test_pkt_access_subprog2(2, skb) != skb->len * 2)
return TC_ACT_SHOT;
if (test_pkt_access_subprog3(3, skb) != skb->len * 3 * skb->ifindex)
return TC_ACT_SHOT;
if (tcp) {
if (test_pkt_write_access_subprog(skb, (void *)tcp - data))
return TC_ACT_SHOT;
if (((void *)(tcp) + 20) > data_end || proto != 6)
return TC_ACT_SHOT;
barrier(); /* to force ordering of checks */
if (((void *)(tcp) + 18) > data_end)
return TC_ACT_SHOT;
if (tcp->urg_ptr == 123)
return TC_ACT_OK;
}
return TC_ACT_UNSPEC;
}
|
