1 /*
2  * NOTE: This example is works on x86 and powerpc.
3  * Here's a sample kernel module showing the use of kprobes to dump a
4  * stack trace and selected registers when _do_fork() is called.
5  *
6  * For more information on theory of operation of kprobes, see
7  * Documentation/kprobes.txt
8  *
9  * You will see the trace data in /var/log/messages and on the console
10  * whenever _do_fork() is invoked to create a new process.
11  */
12 
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/kprobes.h>
16 
17 /* For each probe you need to allocate a kprobe structure */
18 static struct kprobe kp = {
19 	.symbol_name	= "_do_fork",
20 };
21 
22 /* kprobe pre_handler: called just before the probed instruction is executed */
23 static int handler_pre(struct kprobe *p, struct pt_regs *regs)
24 {
25 #ifdef CONFIG_X86
26 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, ip = %lx,"
27 			" flags = 0x%lx\n",
28 		p->addr, regs->ip, regs->flags);
29 #endif
30 #ifdef CONFIG_PPC
31 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, nip = 0x%lx,"
32 			" msr = 0x%lx\n",
33 		p->addr, regs->nip, regs->msr);
34 #endif
35 #ifdef CONFIG_MIPS
36 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, epc = 0x%lx,"
37 			" status = 0x%lx\n",
38 		p->addr, regs->cp0_epc, regs->cp0_status);
39 #endif
40 #ifdef CONFIG_TILEGX
41 	printk(KERN_INFO "pre_handler: p->addr = 0x%p, pc = 0x%lx,"
42 			" ex1 = 0x%lx\n",
43 		p->addr, regs->pc, regs->ex1);
44 #endif
45 
46 	/* A dump_stack() here will give a stack backtrace */
47 	return 0;
48 }
49 
50 /* kprobe post_handler: called after the probed instruction is executed */
51 static void handler_post(struct kprobe *p, struct pt_regs *regs,
52 				unsigned long flags)
53 {
54 #ifdef CONFIG_X86
55 	printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
56 		p->addr, regs->flags);
57 #endif
58 #ifdef CONFIG_PPC
59 	printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
60 		p->addr, regs->msr);
61 #endif
62 #ifdef CONFIG_MIPS
63 	printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\n",
64 		p->addr, regs->cp0_status);
65 #endif
66 #ifdef CONFIG_TILEGX
67 	printk(KERN_INFO "post_handler: p->addr = 0x%p, ex1 = 0x%lx\n",
68 		p->addr, regs->ex1);
69 #endif
70 }
71 
72 /*
73  * fault_handler: this is called if an exception is generated for any
74  * instruction within the pre- or post-handler, or when Kprobes
75  * single-steps the probed instruction.
76  */
77 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
78 {
79 	printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
80 		p->addr, trapnr);
81 	/* Return 0 because we don't handle the fault. */
82 	return 0;
83 }
84 
85 static int __init kprobe_init(void)
86 {
87 	int ret;
88 	kp.pre_handler = handler_pre;
89 	kp.post_handler = handler_post;
90 	kp.fault_handler = handler_fault;
91 
92 	ret = register_kprobe(&kp);
93 	if (ret < 0) {
94 		printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
95 		return ret;
96 	}
97 	printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
98 	return 0;
99 }
100 
101 static void __exit kprobe_exit(void)
102 {
103 	unregister_kprobe(&kp);
104 	printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
105 }
106 
107 module_init(kprobe_init)
108 module_exit(kprobe_exit)
109 MODULE_LICENSE("GPL");
110