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 static char symbol[KSYM_NAME_LEN] = "kernel_clone";
  20 module_param_string(symbol, symbol, KSYM_NAME_LEN, 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 __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs)
  29 {
  30 #ifdef CONFIG_X86
  31         pr_info("<%s> 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> 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> 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> p->addr = 0x%p, pc = 0x%lx, pstate = 0x%lx\n",
  44                 p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate);
  45 #endif
  46 #ifdef CONFIG_ARM
  47         pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, cpsr = 0x%lx\n",
  48                 p->symbol_name, p->addr, (long)regs->ARM_pc, (long)regs->ARM_cpsr);
  49 #endif
  50 #ifdef CONFIG_RISCV
  51         pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, status = 0x%lx\n",
  52                 p->symbol_name, p->addr, regs->epc, regs->status);
  53 #endif
  54 #ifdef CONFIG_S390
  55         pr_info("<%s> p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n",
  56                 p->symbol_name, p->addr, regs->psw.addr, regs->flags);
  57 #endif
  58 #ifdef CONFIG_LOONGARCH
  59         pr_info("<%s> p->addr = 0x%p, era = 0x%lx, estat = 0x%lx\n",
  60                 p->symbol_name, p->addr, regs->csr_era, regs->csr_estat);
  61 #endif
  62
  63         /* A dump_stack() here will give a stack backtrace */
  64         return 0;
  65 }
  66
  67 /* kprobe post_handler: called after the probed instruction is executed */
  68 static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs,
  69                                 unsigned long flags)
  70 {
  71 #ifdef CONFIG_X86
  72         pr_info("<%s> p->addr = 0x%p, flags = 0x%lx\n",
  73                 p->symbol_name, p->addr, regs->flags);
  74 #endif
  75 #ifdef CONFIG_PPC
  76         pr_info("<%s> p->addr = 0x%p, msr = 0x%lx\n",
  77                 p->symbol_name, p->addr, regs->msr);
  78 #endif
  79 #ifdef CONFIG_MIPS
  80         pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n",
  81                 p->symbol_name, p->addr, regs->cp0_status);
  82 #endif
  83 #ifdef CONFIG_ARM64
  84         pr_info("<%s> p->addr = 0x%p, pstate = 0x%lx\n",
  85                 p->symbol_name, p->addr, (long)regs->pstate);
  86 #endif
  87 #ifdef CONFIG_ARM
  88         pr_info("<%s> p->addr = 0x%p, cpsr = 0x%lx\n",
  89                 p->symbol_name, p->addr, (long)regs->ARM_cpsr);
  90 #endif
  91 #ifdef CONFIG_RISCV
  92         pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n",
  93                 p->symbol_name, p->addr, regs->status);
  94 #endif
  95 #ifdef CONFIG_S390
  96         pr_info("<%s> p->addr, 0x%p, flags = 0x%lx\n",
  97                 p->symbol_name, p->addr, regs->flags);
  98 #endif
  99 #ifdef CONFIG_LOONGARCH
 100         pr_info("<%s> p->addr = 0x%p, estat = 0x%lx\n",
 101                 p->symbol_name, p->addr, regs->csr_estat);
 102 #endif
 103 }
 104
 105 static int __init kprobe_init(void)
 106 {
 107         int ret;
 108         kp.pre_handler = handler_pre;
 109         kp.post_handler = handler_post;
 110
 111         ret = register_kprobe(&kp);
 112         if (ret < 0) {
 113                 pr_err("register_kprobe failed, returned %d\n", ret);
 114                 return ret;
 115         }
 116         pr_info("Planted kprobe at %p\n", kp.addr);
 117         return 0;
 118 }
 119
 120 static void __exit kprobe_exit(void)
 121 {
 122         unregister_kprobe(&kp);
 123         pr_info("kprobe at %p unregistered\n", kp.addr);
 124 }
 125
 126 module_init(kprobe_init)
 127 module_exit(kprobe_exit)
 128 MODULE_LICENSE("GPL");