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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 | |
37 | struct perf_event * __percpu *sample_hbp; |
38 | |
39 | static char ksym_name[KSYM_NAME_LEN] = "pid_max"; |
40 | module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO); |
41 | MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any" |
42 | " write operations on the kernel symbol"); |
43 | |
44 | static 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 | |
53 | static 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 | |
73 | fail: |
74 | printk(KERN_INFO "Breakpoint registration failed\n"); |
75 | |
76 | return ret; |
77 | } |
78 | |
79 | static 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 | |
85 | module_init(hw_break_module_init); |
86 | module_exit(hw_break_module_exit); |
87 | |
88 | MODULE_LICENSE("GPL"); |
89 | MODULE_AUTHOR("K.Prasad"); |
90 | MODULE_DESCRIPTION("ksym breakpoint"); |
91 |
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