2 * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * usage: insmod data_breakpoint.ko ksym=<ksym_name>
20 * This file is a kernel module that places a breakpoint over ksym_name kernel
21 * variable using Hardware Breakpoint register. The corresponding handler which
22 * prints a backtrace is invoked everytime a write operation is performed on
25 * Copyright (C) IBM Corporation, 2009
27 #include <linux/module.h> /* Needed by all modules */
28 #include <linux/kernel.h> /* Needed for KERN_INFO */
29 #include <linux/init.h> /* Needed for the macros */
30 #include <linux/kallsyms.h>
32 #include <linux/perf_event.h>
33 #include <linux/hw_breakpoint.h>
35 struct perf_event **sample_hbp;
37 static char ksym_name[KSYM_NAME_LEN] = "pid_max";
38 module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
39 MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
40 " write operations on the kernel symbol");
42 static void sample_hbp_handler(struct perf_event *temp, void *data)
44 printk(KERN_INFO "%s value is changed\n", ksym_name);
46 printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
49 static int __init hw_break_module_init(void)
54 addr = kallsyms_lookup_name(ksym_name);
56 sample_hbp = register_wide_hw_breakpoint(addr, HW_BREAKPOINT_LEN_4,
57 HW_BREAKPOINT_W | HW_BREAKPOINT_R,
58 sample_hbp_handler, true);
59 if (IS_ERR(sample_hbp)) {
60 ret = PTR_ERR(sample_hbp);
62 } else if (!sample_hbp) {
67 printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
72 printk(KERN_INFO "Breakpoint registration failed\n");
77 static void __exit hw_break_module_exit(void)
79 unregister_wide_hw_breakpoint(sample_hbp);
80 printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
83 module_init(hw_break_module_init);
84 module_exit(hw_break_module_exit);
86 MODULE_LICENSE("GPL");
87 MODULE_AUTHOR("K.Prasad");
88 MODULE_DESCRIPTION("ksym breakpoint");