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43203993 P |
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 everytime a write operation is performed on | |
23 | * that variable. | |
24 | * | |
25 | * Copyright (C) IBM Corporation, 2009 | |
26 | */ | |
27 | #include <linux/module.h> /* Needed by all modules */ | |
28 | #include <linux/kernel.h> /* Needed for KERN_INFO */ | |
29 | #include <linux/init.h> /* Needed for the macros */ | |
f60d24d2 | 30 | #include <linux/kallsyms.h> |
43203993 | 31 | |
f60d24d2 FW |
32 | #include <linux/perf_event.h> |
33 | #include <linux/hw_breakpoint.h> | |
43203993 | 34 | |
f60d24d2 | 35 | struct perf_event **sample_hbp; |
43203993 P |
36 | |
37 | static char ksym_name[KSYM_NAME_LEN] = "pid_max"; | |
38 | module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO); | |
39 | MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any" | |
40 | " write operations on the kernel symbol"); | |
41 | ||
f60d24d2 | 42 | static void sample_hbp_handler(struct perf_event *temp, void *data) |
43203993 P |
43 | { |
44 | printk(KERN_INFO "%s value is changed\n", ksym_name); | |
45 | dump_stack(); | |
46 | printk(KERN_INFO "Dump stack from sample_hbp_handler\n"); | |
47 | } | |
48 | ||
49 | static int __init hw_break_module_init(void) | |
50 | { | |
51 | int ret; | |
f60d24d2 | 52 | unsigned long addr; |
43203993 | 53 | |
f60d24d2 | 54 | addr = kallsyms_lookup_name(ksym_name); |
43203993 | 55 | |
f60d24d2 FW |
56 | sample_hbp = register_wide_hw_breakpoint(addr, HW_BREAKPOINT_LEN_4, |
57 | HW_BREAKPOINT_W | HW_BREAKPOINT_R, | |
58 | sample_hbp_handler, true); | |
59 | if (IS_ERR(sample_hbp)) { | |
60 | ret = PTR_ERR(sample_hbp); | |
61 | goto fail; | |
62 | } else if (!sample_hbp) { | |
63 | ret = -EINVAL; | |
64 | goto fail; | |
65 | } | |
43203993 | 66 | |
f60d24d2 | 67 | printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name); |
43203993 P |
68 | |
69 | return 0; | |
f60d24d2 FW |
70 | |
71 | fail: | |
72 | printk(KERN_INFO "Breakpoint registration failed\n"); | |
73 | ||
74 | return ret; | |
43203993 P |
75 | } |
76 | ||
77 | static void __exit hw_break_module_exit(void) | |
78 | { | |
f60d24d2 | 79 | unregister_wide_hw_breakpoint(sample_hbp); |
43203993 P |
80 | printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name); |
81 | } | |
82 | ||
83 | module_init(hw_break_module_init); | |
84 | module_exit(hw_break_module_exit); | |
85 | ||
86 | MODULE_LICENSE("GPL"); | |
87 | MODULE_AUTHOR("K.Prasad"); | |
88 | MODULE_DESCRIPTION("ksym breakpoint"); |