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 | |
24 | static struct perf_event * __percpu *sample_hbp; |
25 | |
26 | static char ksym_name[KSYM_NAME_LEN] = "jiffies" ; |
27 | module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO); |
28 | MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any" |
29 | " write operations on the kernel symbol" ); |
30 | |
31 | static 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 | |
40 | static 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 | |
64 | fail: |
65 | printk(KERN_INFO "Breakpoint registration failed\n" ); |
66 | |
67 | return ret; |
68 | } |
69 | |
70 | static 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 | |
79 | module_init(hw_break_module_init); |
80 | module_exit(hw_break_module_exit); |
81 | |
82 | MODULE_LICENSE("GPL" ); |
83 | MODULE_AUTHOR("K.Prasad" ); |
84 | MODULE_DESCRIPTION("ksym breakpoint" ); |
85 | |