1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * kretprobe_example.c
4  *
5  * Here's a sample kernel module showing the use of return probes to
6  * report the return value and total time taken for probed function
7  * to run.
8  *
9  * usage: insmod kretprobe_example.ko func=<func_name>
10  *
11  * If no func_name is specified, kernel_clone is instrumented
12  *
13  * For more information on theory of operation of kretprobes, see
14  * Documentation/trace/kprobes.rst
15  *
16  * Build and insert the kernel module as done in the kprobe example.
17  * You will see the trace data in /var/log/messages and on the console
18  * whenever the probed function returns. (Some messages may be suppressed
19  * if syslogd is configured to eliminate duplicate messages.)
20  */
21 
22 #include <linux/kernel.h>
23 #include <linux/module.h>
24 #include <linux/kprobes.h>
25 #include <linux/ktime.h>
26 #include <linux/sched.h>
27 
28 static char func_name[KSYM_NAME_LEN] = "kernel_clone";
29 module_param_string(func, func_name, KSYM_NAME_LEN, 0644);
30 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
31 			" function's execution time");
32 
33 /* per-instance private data */
34 struct my_data {
35 	ktime_t entry_stamp;
36 };
37 
38 /* Here we use the entry_hanlder to timestamp function entry */
entry_handler(struct kretprobe_instance * ri,struct pt_regs * regs)39 static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
40 {
41 	struct my_data *data;
42 
43 	if (!current->mm)
44 		return 1;	/* Skip kernel threads */
45 
46 	data = (struct my_data *)ri->data;
47 	data->entry_stamp = ktime_get();
48 	return 0;
49 }
50 NOKPROBE_SYMBOL(entry_handler);
51 
52 /*
53  * Return-probe handler: Log the return value and duration. Duration may turn
54  * out to be zero consistently, depending upon the granularity of time
55  * accounting on the platform.
56  */
ret_handler(struct kretprobe_instance * ri,struct pt_regs * regs)57 static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
58 {
59 	unsigned long retval = regs_return_value(regs);
60 	struct my_data *data = (struct my_data *)ri->data;
61 	s64 delta;
62 	ktime_t now;
63 
64 	now = ktime_get();
65 	delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
66 	pr_info("%s returned %lu and took %lld ns to execute\n",
67 			func_name, retval, (long long)delta);
68 	return 0;
69 }
70 NOKPROBE_SYMBOL(ret_handler);
71 
72 static struct kretprobe my_kretprobe = {
73 	.handler		= ret_handler,
74 	.entry_handler		= entry_handler,
75 	.data_size		= sizeof(struct my_data),
76 	/* Probe up to 20 instances concurrently. */
77 	.maxactive		= 20,
78 };
79 
kretprobe_init(void)80 static int __init kretprobe_init(void)
81 {
82 	int ret;
83 
84 	my_kretprobe.kp.symbol_name = func_name;
85 	ret = register_kretprobe(&my_kretprobe);
86 	if (ret < 0) {
87 		pr_err("register_kretprobe failed, returned %d\n", ret);
88 		return ret;
89 	}
90 	pr_info("Planted return probe at %s: %p\n",
91 			my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
92 	return 0;
93 }
94 
kretprobe_exit(void)95 static void __exit kretprobe_exit(void)
96 {
97 	unregister_kretprobe(&my_kretprobe);
98 	pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
99 
100 	/* nmissed > 0 suggests that maxactive was set too low. */
101 	pr_info("Missed probing %d instances of %s\n",
102 		my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
103 }
104 
105 module_init(kretprobe_init)
106 module_exit(kretprobe_exit)
107 MODULE_LICENSE("GPL");
108