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// 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] = "pid_max";
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
45	hw_breakpoint_init(&attr);
46	attr.bp_addr = kallsyms_lookup_name(ksym_name);
47	attr.bp_len = HW_BREAKPOINT_LEN_4;
48	attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
49
50	sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
51	if (IS_ERR((void __force *)sample_hbp)) {
52		ret = PTR_ERR((void __force *)sample_hbp);
53		goto fail;
54	}
55
56	printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
57
58	return 0;
59
60fail:
61	printk(KERN_INFO "Breakpoint registration failed\n");
62
63	return ret;
64}
65
66static void __exit hw_break_module_exit(void)
67{
68	unregister_wide_hw_breakpoint(sample_hbp);
 
 
 
69	printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
70}
71
72module_init(hw_break_module_init);
73module_exit(hw_break_module_exit);
74
75MODULE_LICENSE("GPL");
76MODULE_AUTHOR("K.Prasad");
77MODULE_DESCRIPTION("ksym breakpoint");