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 #ifdef CONFIG_TILEGX
  41         printk(KERN_INFO "pre_handler: p->addr = 0x%p, pc = 0x%lx,"
  42                         " ex1 = 0x%lx\n",
  43                 p->addr, regs->pc, regs->ex1);
  44 #endif
  45 #ifdef CONFIG_ARM64
  46         pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx,"
  47                         " pstate = 0x%lx\n",
  48                 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate);
  49 #endif
  50
  51         /* A dump_stack() here will give a stack backtrace */
  52         return 0;
  53 }
  54
  55 /* kprobe post_handler: called after the probed instruction is executed */
  56 static void handler_post(struct kprobe *p, struct pt_regs *regs,
  57                                 unsigned long flags)
  58 {
  59 #ifdef CONFIG_X86
  60         printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
  61                 p->addr, regs->flags);
  62 #endif
  63 #ifdef CONFIG_PPC
  64         printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
  65                 p->addr, regs->msr);
  66 #endif
  67 #ifdef CONFIG_MIPS
  68         printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\n",
  69                 p->addr, regs->cp0_status);
  70 #endif
  71 #ifdef CONFIG_TILEGX
  72         printk(KERN_INFO "post_handler: p->addr = 0x%p, ex1 = 0x%lx\n",
  73                 p->addr, regs->ex1);
  74 #endif
  75 #ifdef CONFIG_ARM64
  76         pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n",
  77                 p->symbol_name, p->addr, (long)regs->pstate);
  78 #endif
  79 }
  80
  81 /*
  82  * fault_handler: this is called if an exception is generated for any
  83  * instruction within the pre- or post-handler, or when Kprobes
  84  * single-steps the probed instruction.
  85  */
  86 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
  87 {
  88         printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
  89                 p->addr, trapnr);
  90         /* Return 0 because we don't handle the fault. */
  91         return 0;
  92 }
  93
  94 static int __init kprobe_init(void)
  95 {
  96         int ret;
  97         kp.pre_handler = handler_pre;
  98         kp.post_handler = handler_post;
  99         kp.fault_handler = handler_fault;
 100
 101         ret = register_kprobe(&kp);
 102         if (ret < 0) {
 103                 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
 104                 return ret;
 105         }
 106         printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
 107         return 0;
 108 }
 109
 110 static void __exit kprobe_exit(void)
 111 {
 112         unregister_kprobe(&kp);
 113         printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
 114 }
 115
 116 module_init(kprobe_init)
 117 module_exit(kprobe_exit)
 118 MODULE_LICENSE("GPL");