1 /*
2 * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
3 *
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.
8 *
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.
13 *
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.
17 *
18 * usage: insmod data_breakpoint.ko ksym=<ksym_name>
19 *
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 every time a write operation is performed on
23 * that variable.
24 *
25 * Copyright (C) IBM Corporation, 2009
26 *
27 * Author: K.Prasad <prasad@linux.vnet.ibm.com>
28 */
29 #include <linux/module.h> /* Needed by all modules */
30 #include <linux/kernel.h> /* Needed for KERN_INFO */
31 #include <linux/init.h> /* Needed for the macros */
32 #include <linux/kallsyms.h>
33
34 #include <linux/perf_event.h>
35 #include <linux/hw_breakpoint.h>
36
37 struct perf_event * __percpu *sample_hbp;
38
39 static char ksym_name[KSYM_NAME_LEN] = "pid_max";
40 module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
41 MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
42 " write operations on the kernel symbol");
43
sample_hbp_handler(struct perf_event * bp,struct perf_sample_data * data,struct pt_regs * regs)44 static void sample_hbp_handler(struct perf_event *bp,
45 struct perf_sample_data *data,
46 struct pt_regs *regs)
47 {
48 printk(KERN_INFO "%s value is changed\n", ksym_name);
49 dump_stack();
50 printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
51 }
52
hw_break_module_init(void)53 static int __init hw_break_module_init(void)
54 {
55 int ret;
56 struct perf_event_attr attr;
57
58 hw_breakpoint_init(&attr);
59 attr.bp_addr = kallsyms_lookup_name(ksym_name);
60 attr.bp_len = HW_BREAKPOINT_LEN_4;
61 attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
62
63 sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
64 if (IS_ERR((void __force *)sample_hbp)) {
65 ret = PTR_ERR((void __force *)sample_hbp);
66 goto fail;
67 }
68
69 printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
70
71 return 0;
72
73 fail:
74 printk(KERN_INFO "Breakpoint registration failed\n");
75
76 return ret;
77 }
78
hw_break_module_exit(void)79 static void __exit hw_break_module_exit(void)
80 {
81 unregister_wide_hw_breakpoint(sample_hbp);
82 printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
83 }
84
85 module_init(hw_break_module_init);
86 module_exit(hw_break_module_exit);
87
88 MODULE_LICENSE("GPL");
89 MODULE_AUTHOR("K.Prasad");
90 MODULE_DESCRIPTION("ksym breakpoint");
91