samples/kprobes/kretprobe_example.c

   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, _do_fork is instrumented
  12  *
  13  * For more information on theory of operation of kretprobes, see
  14  * Documentation/kprobes.txt
  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/limits.h>
  27 #include <linux/sched.h>
  28
  29 static char func_name[NAME_MAX] = "_do_fork";
  30 module_param_string(func, func_name, NAME_MAX, S_IRUGO);
  31 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
  32                         " function's execution time");
  33
  34 /* per-instance private data */
  35 struct my_data {
  36         ktime_t entry_stamp;
  37 };
  38
  39 /* Here we use the entry_hanlder to timestamp function entry */
  40 static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
  41 {
  42         struct my_data *data;
  43
  44         if (!current->mm)
  45                 return 1;       /* Skip kernel threads */
  46
  47         data = (struct my_data *)ri->data;
  48         data->entry_stamp = ktime_get();
  49         return 0;
  50 }
  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  */
  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
  71 static struct kretprobe my_kretprobe = {
  72         .handler                = ret_handler,
  73         .entry_handler          = entry_handler,
  74         .data_size              = sizeof(struct my_data),
  75         /* Probe up to 20 instances concurrently. */
  76         .maxactive              = 20,
  77 };
  78
  79 static int __init kretprobe_init(void)
  80 {
  81         int ret;
  82
  83         my_kretprobe.kp.symbol_name = func_name;
  84         ret = register_kretprobe(&my_kretprobe);
  85         if (ret < 0) {
  86                 pr_err("register_kretprobe failed, returned %d\n", ret);
  87                 return -1;
  88         }
  89         pr_info("Planted return probe at %s: %p\n",
  90                         my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
  91         return 0;
  92 }
  93
  94 static void __exit kretprobe_exit(void)
  95 {
  96         unregister_kretprobe(&my_kretprobe);
  97         pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
  98
  99         /* nmissed > 0 suggests that maxactive was set too low. */
 100         pr_info("Missed probing %d instances of %s\n",
 101                 my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
 102 }
 103
 104 module_init(kretprobe_init)
 105 module_exit(kretprobe_exit)
 106 MODULE_LICENSE("GPL");