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K.Prasad43203992009-06-01 23:46:20 +05301/*
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 everytime a write operation is performed on
23 * that variable.
24 *
25 * Copyright (C) IBM Corporation, 2009
K.Prasadba6909b2009-11-23 21:17:13 +053026 *
27 * Author: K.Prasad <prasad@linux.vnet.ibm.com>
K.Prasad43203992009-06-01 23:46:20 +053028 */
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 */
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010032#include <linux/kallsyms.h>
K.Prasad43203992009-06-01 23:46:20 +053033
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010034#include <linux/perf_event.h>
35#include <linux/hw_breakpoint.h>
K.Prasad43203992009-06-01 23:46:20 +053036
Tejun Heo44ee6352010-02-17 10:50:50 +090037struct perf_event * __percpu *sample_hbp;
K.Prasad43203992009-06-01 23:46:20 +053038
39static char ksym_name[KSYM_NAME_LEN] = "pid_max";
40module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
41MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
42 " write operations on the kernel symbol");
43
Frederic Weisbeckerb326e952009-12-05 09:44:31 +010044static void sample_hbp_handler(struct perf_event *bp, int nmi,
45 struct perf_sample_data *data,
46 struct pt_regs *regs)
K.Prasad43203992009-06-01 23:46:20 +053047{
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
53static int __init hw_break_module_init(void)
54{
55 int ret;
Frederic Weisbeckerb326e952009-12-05 09:44:31 +010056 struct perf_event_attr attr;
K.Prasad43203992009-06-01 23:46:20 +053057
Frederic Weisbeckerb326e952009-12-05 09:44:31 +010058 hw_breakpoint_init(&attr);
Frederic Weisbeckerdd1853c2009-11-27 04:55:54 +010059 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;
K.Prasad43203992009-06-01 23:46:20 +053062
Frederic Weisbeckerdd1853c2009-11-27 04:55:54 +010063 sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
Tejun Heo44ee6352010-02-17 10:50:50 +090064 if (IS_ERR((void __force *)sample_hbp)) {
65 ret = PTR_ERR((void __force *)sample_hbp);
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010066 goto fail;
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010067 }
K.Prasad43203992009-06-01 23:46:20 +053068
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010069 printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
K.Prasad43203992009-06-01 23:46:20 +053070
71 return 0;
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010072
73fail:
74 printk(KERN_INFO "Breakpoint registration failed\n");
75
76 return ret;
K.Prasad43203992009-06-01 23:46:20 +053077}
78
79static void __exit hw_break_module_exit(void)
80{
Frederic Weisbeckerf60d24d2009-11-10 10:17:07 +010081 unregister_wide_hw_breakpoint(sample_hbp);
K.Prasad43203992009-06-01 23:46:20 +053082 printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
83}
84
85module_init(hw_break_module_init);
86module_exit(hw_break_module_exit);
87
88MODULE_LICENSE("GPL");
89MODULE_AUTHOR("K.Prasad");
90MODULE_DESCRIPTION("ksym breakpoint");