2 * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
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.
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.
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.
18 * usage: insmod data_breakpoint.ko ksym=<ksym_name>
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
25 * Copyright (C) IBM Corporation, 2009
27 * Author: K.Prasad <prasad@linux.vnet.ibm.com>
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>
34 #include <linux/perf_event.h>
35 #include <linux/hw_breakpoint.h>
37 struct perf_event
**sample_hbp
;
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");
44 static void sample_hbp_handler(struct perf_event
*temp
, void *data
)
46 printk(KERN_INFO
"%s value is changed\n", ksym_name
);
48 printk(KERN_INFO
"Dump stack from sample_hbp_handler\n");
51 static int __init
hw_break_module_init(void)
54 DEFINE_BREAKPOINT_ATTR(attr
);
56 attr
.bp_addr
= kallsyms_lookup_name(ksym_name
);
57 attr
.bp_len
= HW_BREAKPOINT_LEN_4
;
58 attr
.bp_type
= HW_BREAKPOINT_W
| HW_BREAKPOINT_R
;
60 sample_hbp
= register_wide_hw_breakpoint(&attr
, sample_hbp_handler
);
61 if (IS_ERR(sample_hbp
)) {
62 ret
= PTR_ERR(sample_hbp
);
66 printk(KERN_INFO
"HW Breakpoint for %s write installed\n", ksym_name
);
71 printk(KERN_INFO
"Breakpoint registration failed\n");
76 static void __exit
hw_break_module_exit(void)
78 unregister_wide_hw_breakpoint(sample_hbp
);
79 printk(KERN_INFO
"HW Breakpoint for %s write uninstalled\n", ksym_name
);
82 module_init(hw_break_module_init
);
83 module_exit(hw_break_module_exit
);
85 MODULE_LICENSE("GPL");
86 MODULE_AUTHOR("K.Prasad");
87 MODULE_DESCRIPTION("ksym breakpoint");