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         pr_info("<%s> pre_handler: p->addr = 0x%p, ip = %lx, flags = 0x%lx\n",
  31                 p->symbol_name, p->addr, regs->ip, regs->flags);
  32 #endif
  33 #ifdef CONFIG_PPC
  34         pr_info("<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n",
  35                 p->symbol_name, p->addr, regs->nip, regs->msr);
  36 #endif
  37 #ifdef CONFIG_MIPS
  38         pr_info("<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n",
  39                 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status);
  40 #endif
  41 #ifdef CONFIG_TILEGX
  42         pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx, ex1 = 0x%lx\n",
  43                 p->symbol_name, 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         pr_info("<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n",
  61                 p->symbol_name, p->addr, regs->flags);
  62 #endif
  63 #ifdef CONFIG_PPC
  64         pr_info("<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n",
  65                 p->symbol_name, p->addr, regs->msr);
  66 #endif
  67 #ifdef CONFIG_MIPS
  68         pr_info("<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n",
  69                 p->symbol_name, p->addr, regs->cp0_status);
  70 #endif
  71 #ifdef CONFIG_TILEGX
  72         pr_info("<%s> post_handler: p->addr = 0x%p, ex1 = 0x%lx\n",
  73                 p->symbol_name, 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         pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr);
  89         /* Return 0 because we don't handle the fault. */
  90         return 0;
  91 }
  92
  93 static int __init kprobe_init(void)
  94 {
  95         int ret;
  96         kp.pre_handler = handler_pre;
  97         kp.post_handler = handler_post;
  98         kp.fault_handler = handler_fault;
  99
 100         ret = register_kprobe(&kp);
 101         if (ret < 0) {
 102                 pr_err("register_kprobe failed, returned %d\n", ret);
 103                 return ret;
 104         }
 105         pr_info("Planted kprobe at %p\n", kp.addr);
 106         return 0;
 107 }
 108
 109 static void __exit kprobe_exit(void)
 110 {
 111         unregister_kprobe(&kp);
 112         pr_info("kprobe at %p unregistered\n", kp.addr);
 113 }
 114
 115 module_init(kprobe_init)
 116 module_exit(kprobe_exit)
 117 MODULE_LICENSE("GPL");