1 /* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 */
7 #include <linux/skbuff.h>
8 #include <linux/netdevice.h>
9 #include <uapi/linux/bpf.h>
10 #include <linux/version.h>
11 #include <bpf/bpf_helpers.h>
12 #include <bpf/bpf_tracing.h>
13
14 #define _(P) \
15 ({ \
16 typeof(P) val = 0; \
17 bpf_probe_read_kernel(&val, sizeof(val), &(P)); \
18 val; \
19 })
20
21 /* kprobe is NOT a stable ABI
22 * kernel functions can be removed, renamed or completely change semantics.
23 * Number of arguments and their positions can change, etc.
24 * In such case this bpf+kprobe example will no longer be meaningful
25 */
26 SEC("kprobe/__netif_receive_skb_core")
bpf_prog1(struct pt_regs * ctx)27 int bpf_prog1(struct pt_regs *ctx)
28 {
29 /* attaches to kprobe __netif_receive_skb_core,
30 * looks for packets on loobpack device and prints them
31 */
32 char devname[IFNAMSIZ];
33 struct net_device *dev;
34 struct sk_buff *skb;
35 int len;
36
37 /* non-portable! works for the given kernel only */
38 bpf_probe_read_kernel(&skb, sizeof(skb), (void *)PT_REGS_PARM1(ctx));
39 dev = _(skb->dev);
40 len = _(skb->len);
41
42 bpf_probe_read_kernel(devname, sizeof(devname), dev->name);
43
44 if (devname[0] == 'l' && devname[1] == 'o') {
45 char fmt[] = "skb %p len %d\n";
46 /* using bpf_trace_printk() for DEBUG ONLY */
47 bpf_trace_printk(fmt, sizeof(fmt), skb, len);
48 }
49
50 return 0;
51 }
52
53 char _license[] SEC("license") = "GPL";
54 u32 _version SEC("version") = LINUX_VERSION_CODE;
55