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, 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_handler to timestamp function entry */
  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  */
  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
  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
  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_DESCRIPTION("sample kernel module showing the use of return probes");
 108 MODULE_LICENSE("GPL");