LXR linux/samples/hw_breakpoint/data

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
   4 *
   5 * usage: insmod data_breakpoint.ko ksym=<ksym_name>
   6 *
   7 * This file is a kernel module that places a breakpoint over ksym_name kernel
   8 * variable using Hardware Breakpoint register. The corresponding handler which
   9 * prints a backtrace is invoked every time a write operation is performed on
  10 * that variable.
  11 *
  12 * Copyright (C) IBM Corporation, 2009
  13 *
  14 * Author: K.Prasad <prasad@linux.vnet.ibm.com>
  15 */
  16#include <linux/module.h>       /* Needed by all modules */
  17#include <linux/kernel.h>       /* Needed for KERN_INFO */
  18#include <linux/init.h>         /* Needed for the macros */
  19#include <linux/kallsyms.h>
  20
  21#include <linux/perf_event.h>
  22#include <linux/hw_breakpoint.h>
  23
  24struct perf_event * __percpu *sample_hbp;
  25
  26static char ksym_name[KSYM_NAME_LEN] = "jiffies";
  27module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
  28MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
  29                        " write operations on the kernel symbol");
  30
  31static void sample_hbp_handler(struct perf_event *bp,
  32                               struct perf_sample_data *data,
  33                               struct pt_regs *regs)
  34{
  35        printk(KERN_INFO "%s value is changed\n", ksym_name);
  36        dump_stack();
  37        printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
  38}
  39
  40static int __init hw_break_module_init(void)
  41{
  42        int ret;
  43        struct perf_event_attr attr;
  44        void *addr = __symbol_get(ksym_name);
  45
  46        if (!addr)
  47                return -ENXIO;
  48
  49        hw_breakpoint_init(&attr);
  50        attr.bp_addr = (unsigned long)addr;
  51        attr.bp_len = HW_BREAKPOINT_LEN_4;
  52        attr.bp_type = HW_BREAKPOINT_W;
  53
  54        sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
  55        if (IS_ERR((void __force *)sample_hbp)) {
  56                ret = PTR_ERR((void __force *)sample_hbp);
  57                goto fail;
  58        }
  59
  60        printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
  61
  62        return 0;
  63
  64fail:
  65        printk(KERN_INFO "Breakpoint registration failed\n");
  66
  67        return ret;
  68}
  69
  70static void __exit hw_break_module_exit(void)
  71{
  72        unregister_wide_hw_breakpoint(sample_hbp);
  73        symbol_put(ksym_name);
  74        printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
  75}
  76
  77module_init(hw_break_module_init);
  78module_exit(hw_break_module_exit);
  79
  80MODULE_LICENSE("GPL");
  81MODULE_AUTHOR("K.Prasad");
  82MODULE_DESCRIPTION("ksym breakpoint");
  83