samples/kprobes/kprobe_example.c

   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
  41         /* A dump_stack() here will give a stack backtrace */
  42         return 0;
  43 }
  44
  45 /* kprobe post_handler: called after the probed instruction is executed */
  46 static void handler_post(struct kprobe *p, struct pt_regs *regs,
  47                                 unsigned long flags)
  48 {
  49 #ifdef CONFIG_X86
  50         printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
  51                 p->addr, regs->flags);
  52 #endif
  53 #ifdef CONFIG_PPC
  54         printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
  55                 p->addr, regs->msr);
  56 #endif
  57 #ifdef CONFIG_MIPS
  58         printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\n",
  59                 p->addr, regs->cp0_status);
  60 #endif
  61 }
  62
  63 /*
  64  * fault_handler: this is called if an exception is generated for any
  65  * instruction within the pre- or post-handler, or when Kprobes
  66  * single-steps the probed instruction.
  67  */
  68 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
  69 {
  70         printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
  71                 p->addr, trapnr);
  72         /* Return 0 because we don't handle the fault. */
  73         return 0;
  74 }
  75
  76 static int __init kprobe_init(void)
  77 {
  78         int ret;
  79         kp.pre_handler = handler_pre;
  80         kp.post_handler = handler_post;
  81         kp.fault_handler = handler_fault;
  82
  83         ret = register_kprobe(&kp);
  84         if (ret < 0) {
  85                 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
  86                 return ret;
  87         }
  88         printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
  89         return 0;
  90 }
  91
  92 static void __exit kprobe_exit(void)
  93 {
  94         unregister_kprobe(&kp);
  95         printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
  96 }
  97
  98 module_init(kprobe_init)
  99 module_exit(kprobe_exit)
 100 MODULE_LICENSE("GPL");