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(symbol: ksym_name);
45
46 if (!addr)
47 return -ENXIO;
48
49 hw_breakpoint_init(attr: &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: &attr, triggered: sample_hbp_handler, NULL);
55 if (IS_ERR(ptr: (void __force *)sample_hbp)) {
56 ret = PTR_ERR(ptr: (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(cpu_events: sample_hbp);
73#ifdef CONFIG_MODULE_UNLOAD
74 __symbol_put(symbol: 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");
85

source code of linux/samples/hw_breakpoint/data_breakpoint.c