samples/kprobes/jprobe_example.c

   1 /*
   2  * Here's a sample kernel module showing the use of jprobes to dump
   3  * the arguments of _do_fork().
   4  *
   5  * For more information on theory of operation of jprobes, see
   6  * Documentation/kprobes.txt
   7  *
   8  * Build and insert the kernel module as done in the kprobe example.
   9  * You will see the trace data in /var/log/messages and on the
  10  * console whenever _do_fork() is invoked to create a new process.
  11  * (Some messages may be suppressed if syslogd is configured to
  12  * eliminate duplicate messages.)
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/module.h>
  17 #include <linux/kprobes.h>
  18
  19 /*
  20  * Jumper probe for _do_fork.
  21  * Mirror principle enables access to arguments of the probed routine
  22  * from the probe handler.
  23  */
  24
  25 /* Proxy routine having the same arguments as actual _do_fork() routine */
  26 static long j_do_fork(unsigned long clone_flags, unsigned long stack_start,
  27               unsigned long stack_size, int __user *parent_tidptr,
  28               int __user *child_tidptr)
  29 {
  30         pr_info("jprobe: clone_flags = 0x%lx, stack_start = 0x%lx "
  31                 "stack_size = 0x%lx\n", clone_flags, stack_start, stack_size);
  32
  33         /* Always end with a call to jprobe_return(). */
  34         jprobe_return();
  35         return 0;
  36 }
  37
  38 static struct jprobe my_jprobe = {
  39         .entry                  = j_do_fork,
  40         .kp = {
  41                 .symbol_name    = "_do_fork",
  42         },
  43 };
  44
  45 static int __init jprobe_init(void)
  46 {
  47         int ret;
  48
  49         ret = register_jprobe(&my_jprobe);
  50         if (ret < 0) {
  51                 printk(KERN_INFO "register_jprobe failed, returned %d\n", ret);
  52                 return -1;
  53         }
  54         printk(KERN_INFO "Planted jprobe at %p, handler addr %p\n",
  55                my_jprobe.kp.addr, my_jprobe.entry);
  56         return 0;
  57 }
  58
  59 static void __exit jprobe_exit(void)
  60 {
  61         unregister_jprobe(&my_jprobe);
  62         printk(KERN_INFO "jprobe at %p unregistered\n", my_jprobe.kp.addr);
  63 }
  64
  65 module_init(jprobe_init)
  66 module_exit(jprobe_exit)
  67 MODULE_LICENSE("GPL");