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
24static struct 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#ifdef CONFIG_MODULE_UNLOAD
74	__symbol_put(ksym_name);
75#endif
76	printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
77}
78
79module_init(hw_break_module_init);
80module_exit(hw_break_module_exit);
81
82MODULE_LICENSE("GPL");
83MODULE_AUTHOR("K.Prasad");
84MODULE_DESCRIPTION("ksym breakpoint");

 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
37struct perf_event * __percpu *sample_hbp;
38
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
44static 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
53static 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
73fail:
74	printk(KERN_INFO "Breakpoint registration failed\n");
75
76	return ret;
77}
78
79static 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
85module_init(hw_break_module_init);
86module_exit(hw_break_module_exit);
87
88MODULE_LICENSE("GPL");
89MODULE_AUTHOR("K.Prasad");
90MODULE_DESCRIPTION("ksym breakpoint");