samples/kprobes/kprobe_example.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * NOTE: This example is works on x86 and powerpc.
   4  * Here's a sample kernel module showing the use of kprobes to dump a
   5  * stack trace and selected registers when _do_fork() is called.
   6  *
   7  * For more information on theory of operation of kprobes, see
   8  * Documentation/kprobes.txt
   9  *
  10  * You will see the trace data in /var/log/messages and on the console
  11  * whenever _do_fork() is invoked to create a new process.
  12  */
  13
  14 #include <linux/kernel.h>
  15 #include <linux/module.h>
  16 #include <linux/kprobes.h>
  17
  18 #define MAX_SYMBOL_LEN  64
  19 static char symbol[MAX_SYMBOL_LEN] = "_do_fork";
  20 module_param_string(symbol, symbol, sizeof(symbol), 0644);
  21
  22 /* For each probe you need to allocate a kprobe structure */
  23 static struct kprobe kp = {
  24         .symbol_name    = symbol,
  25 };
  26
  27 /* kprobe pre_handler: called just before the probed instruction is executed */
  28 static int handler_pre(struct kprobe *p, struct pt_regs *regs)
  29 {
  30 #ifdef CONFIG_X86
  31         pr_info("<%s> pre_handler: p->addr = 0x%p, ip = %lx, flags = 0x%lx\n",
  32                 p->symbol_name, p->addr, regs->ip, regs->flags);
  33 #endif
  34 #ifdef CONFIG_PPC
  35         pr_info("<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n",
  36                 p->symbol_name, p->addr, regs->nip, regs->msr);
  37 #endif
  38 #ifdef CONFIG_MIPS
  39         pr_info("<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n",
  40                 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status);
  41 #endif
  42 #ifdef CONFIG_ARM64
  43         pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx,"
  44                         " pstate = 0x%lx\n",
  45                 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate);
  46 #endif
  47 #ifdef CONFIG_S390
  48         pr_info("<%s> pre_handler: p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n",
  49                 p->symbol_name, p->addr, regs->psw.addr, regs->flags);
  50 #endif
  51
  52         /* A dump_stack() here will give a stack backtrace */
  53         return 0;
  54 }
  55
  56 /* kprobe post_handler: called after the probed instruction is executed */
  57 static void handler_post(struct kprobe *p, struct pt_regs *regs,
  58                                 unsigned long flags)
  59 {
  60 #ifdef CONFIG_X86
  61         pr_info("<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n",
  62                 p->symbol_name, p->addr, regs->flags);
  63 #endif
  64 #ifdef CONFIG_PPC
  65         pr_info("<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n",
  66                 p->symbol_name, p->addr, regs->msr);
  67 #endif
  68 #ifdef CONFIG_MIPS
  69         pr_info("<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n",
  70                 p->symbol_name, p->addr, regs->cp0_status);
  71 #endif
  72 #ifdef CONFIG_ARM64
  73         pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n",
  74                 p->symbol_name, p->addr, (long)regs->pstate);
  75 #endif
  76 #ifdef CONFIG_S390
  77         pr_info("<%s> pre_handler: p->addr, 0x%p, flags = 0x%lx\n",
  78                 p->symbol_name, p->addr, regs->flags);
  79 #endif
  80 }
  81
  82 /*
  83  * fault_handler: this is called if an exception is generated for any
  84  * instruction within the pre- or post-handler, or when Kprobes
  85  * single-steps the probed instruction.
  86  */
  87 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
  88 {
  89         pr_info("fault_handler: p->addr = 0x%p, trap #%dn", 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                 pr_err("register_kprobe failed, returned %d\n", ret);
 104                 return ret;
 105         }
 106         pr_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         pr_info("kprobe at %p unregistered\n", kp.addr);
 114 }
 115
 116 module_init(kprobe_init)
 117 module_exit(kprobe_exit)
 118 MODULE_LICENSE("GPL");