samples/kprobes/kprobe_example.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Here's a sample kernel module showing the use of kprobes to dump a
   4  * stack trace and selected registers when kernel_clone() is called.
   5  *
   6  * For more information on theory of operation of kprobes, see
   7  * Documentation/trace/kprobes.rst
   8  *
   9  * You will see the trace data in /var/log/messages and on the console
  10  * whenever kernel_clone() is invoked to create a new process.
  11  */
  12
  13 #define pr_fmt(fmt) "%s: " fmt, __func__
  14
  15 #include <linux/kernel.h>
  16 #include <linux/module.h>
  17 #include <linux/kprobes.h>
  18
  19 #define MAX_SYMBOL_LEN  64
  20 static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
  21 module_param_string(symbol, symbol, sizeof(symbol), 0644);
  22
  23 /* For each probe you need to allocate a kprobe structure */
  24 static struct kprobe kp = {
  25         .symbol_name    = symbol,
  26 };
  27
  28 /* kprobe pre_handler: called just before the probed instruction is executed */
  29 static int __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs)
  30 {
  31 #ifdef CONFIG_X86
  32         pr_info("<%s> p->addr = 0x%p, ip = %lx, flags = 0x%lx\n",
  33                 p->symbol_name, p->addr, regs->ip, regs->flags);
  34 #endif
  35 #ifdef CONFIG_PPC
  36         pr_info("<%s> p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n",
  37                 p->symbol_name, p->addr, regs->nip, regs->msr);
  38 #endif
  39 #ifdef CONFIG_MIPS
  40         pr_info("<%s> p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n",
  41                 p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status);
  42 #endif
  43 #ifdef CONFIG_ARM64
  44         pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, pstate = 0x%lx\n",
  45                 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate);
  46 #endif
  47 #ifdef CONFIG_ARM
  48         pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, cpsr = 0x%lx\n",
  49                 p->symbol_name, p->addr, (long)regs->ARM_pc, (long)regs->ARM_cpsr);
  50 #endif
  51 #ifdef CONFIG_RISCV
  52         pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, status = 0x%lx\n",
  53                 p->symbol_name, p->addr, regs->epc, regs->status);
  54 #endif
  55 #ifdef CONFIG_S390
  56         pr_info("<%s> p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n",
  57                 p->symbol_name, p->addr, regs->psw.addr, regs->flags);
  58 #endif
  59
  60         /* A dump_stack() here will give a stack backtrace */
  61         return 0;
  62 }
  63
  64 /* kprobe post_handler: called after the probed instruction is executed */
  65 static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs,
  66                                 unsigned long flags)
  67 {
  68 #ifdef CONFIG_X86
  69         pr_info("<%s> p->addr = 0x%p, flags = 0x%lx\n",
  70                 p->symbol_name, p->addr, regs->flags);
  71 #endif
  72 #ifdef CONFIG_PPC
  73         pr_info("<%s> p->addr = 0x%p, msr = 0x%lx\n",
  74                 p->symbol_name, p->addr, regs->msr);
  75 #endif
  76 #ifdef CONFIG_MIPS
  77         pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n",
  78                 p->symbol_name, p->addr, regs->cp0_status);
  79 #endif
  80 #ifdef CONFIG_ARM64
  81         pr_info("<%s> p->addr = 0x%p, pstate = 0x%lx\n",
  82                 p->symbol_name, p->addr, (long)regs->pstate);
  83 #endif
  84 #ifdef CONFIG_ARM
  85         pr_info("<%s> p->addr = 0x%p, cpsr = 0x%lx\n",
  86                 p->symbol_name, p->addr, (long)regs->ARM_cpsr);
  87 #endif
  88 #ifdef CONFIG_RISCV
  89         pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n",
  90                 p->symbol_name, p->addr, regs->status);
  91 #endif
  92 #ifdef CONFIG_S390
  93         pr_info("<%s> p->addr, 0x%p, flags = 0x%lx\n",
  94                 p->symbol_name, p->addr, regs->flags);
  95 #endif
  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
 104         ret = register_kprobe(&kp);
 105         if (ret < 0) {
 106                 pr_err("register_kprobe failed, returned %d\n", ret);
 107                 return ret;
 108         }
 109         pr_info("Planted kprobe at %p\n", kp.addr);
 110         return 0;
 111 }
 112
 113 static void __exit kprobe_exit(void)
 114 {
 115         unregister_kprobe(&kp);
 116         pr_info("kprobe at %p unregistered\n", kp.addr);
 117 }
 118
 119 module_init(kprobe_init)
 120 module_exit(kprobe_exit)
 121 MODULE_LICENSE("GPL");