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 #define MAX_SYMBOL_LEN  64
  18 static char symbol[MAX_SYMBOL_LEN] = "_do_fork";
  19 module_param_string(symbol, symbol, sizeof(symbol), 0644);
  20
  21 /* For each probe you need to allocate a kprobe structure */
  22 static struct kprobe kp = {
  23         .symbol_name    = symbol,
  24 };
  25
  26 /* kprobe pre_handler: called just before the probed instruction is executed */
  27 static int handler_pre(struct kprobe *p, struct pt_regs *regs)
  28 {
  29 #ifdef CONFIG_X86
  30         printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, ip = %lx,"
  31                         " flags = 0x%lx\n",
  32                 p->symbol_name, p->addr, regs->ip, regs->flags);
  33 #endif
  34 #ifdef CONFIG_PPC
  35         printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx,"
  36                         " msr = 0x%lx\n",
  37                 p->symbol_name, p->addr, regs->nip, regs->msr);
  38 #endif
  39 #ifdef CONFIG_MIPS
  40         printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx,"
  41                         " status = 0x%lx\n",
  42                 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status);
  43 #endif
  44 #ifdef CONFIG_TILEGX
  45         printk(KERN_INFO "<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx,"
  46                         " ex1 = 0x%lx\n",
  47                 p->symbol_name, p->addr, regs->pc, regs->ex1);
  48 #endif
  49 #ifdef CONFIG_ARM64
  50         pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx,"
  51                         " pstate = 0x%lx\n",
  52                 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate);
  53 #endif
  54
  55         /* A dump_stack() here will give a stack backtrace */
  56         return 0;
  57 }
  58
  59 /* kprobe post_handler: called after the probed instruction is executed */
  60 static void handler_post(struct kprobe *p, struct pt_regs *regs,
  61                                 unsigned long flags)
  62 {
  63 #ifdef CONFIG_X86
  64         printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n",
  65                 p->symbol_name, p->addr, regs->flags);
  66 #endif
  67 #ifdef CONFIG_PPC
  68         printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n",
  69                 p->symbol_name, p->addr, regs->msr);
  70 #endif
  71 #ifdef CONFIG_MIPS
  72         printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n",
  73                 p->symbol_name, p->addr, regs->cp0_status);
  74 #endif
  75 #ifdef CONFIG_TILEGX
  76         printk(KERN_INFO "<%s> post_handler: p->addr = 0x%p, ex1 = 0x%lx\n",
  77                 p->symbol_name, p->addr, regs->ex1);
  78 #endif
  79 #ifdef CONFIG_ARM64
  80         pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n",
  81                 p->symbol_name, p->addr, (long)regs->pstate);
  82 #endif
  83 }
  84
  85 /*
  86  * fault_handler: this is called if an exception is generated for any
  87  * instruction within the pre- or post-handler, or when Kprobes
  88  * single-steps the probed instruction.
  89  */
  90 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
  91 {
  92         printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
  93                 p->addr, trapnr);
  94         /* Return 0 because we don't handle the fault. */
  95         return 0;
  96 }
  97
  98 static int __init kprobe_init(void)
  99 {
 100         int ret;
 101         kp.pre_handler = handler_pre;
 102         kp.post_handler = handler_post;
 103         kp.fault_handler = handler_fault;
 104
 105         ret = register_kprobe(&kp);
 106         if (ret < 0) {
 107                 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
 108                 return ret;
 109         }
 110         printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
 111         return 0;
 112 }
 113
 114 static void __exit kprobe_exit(void)
 115 {
 116         unregister_kprobe(&kp);
 117         printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
 118 }
 119
 120 module_init(kprobe_init)
 121 module_exit(kprobe_exit)
 122 MODULE_LICENSE("GPL");