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/*
* data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* usage: insmod data_breakpoint.ko ksym=<ksym_name>
*
* This file is a kernel module that places a breakpoint over ksym_name kernel
* variable using Hardware Breakpoint register. The corresponding handler which
* prints a backtrace is invoked everytime a write operation is performed on
* that variable.
*
* Copyright (C) IBM Corporation, 2009
*
* Author: K.Prasad <prasad@linux.vnet.ibm.com>
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
#include <linux/init.h> /* Needed for the macros */
#include <linux/kallsyms.h>
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
struct perf_event **sample_hbp;
static char ksym_name[KSYM_NAME_LEN] = "pid_max";
module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
" write operations on the kernel symbol");
static void sample_hbp_handler(struct perf_event *bp, int nmi,
struct perf_sample_data *data,
struct pt_regs *regs)
{
printk(KERN_INFO "%s value is changed\n", ksym_name);
dump_stack();
printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
}
static int __init hw_break_module_init(void)
{
int ret;
struct perf_event_attr attr;
hw_breakpoint_init(&attr);
attr.bp_addr = kallsyms_lookup_name(ksym_name);
attr.bp_len = HW_BREAKPOINT_LEN_4;
attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
if (IS_ERR(sample_hbp)) {
ret = PTR_ERR(sample_hbp);
goto fail;
}
printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
return 0;
fail:
printk(KERN_INFO "Breakpoint registration failed\n");
return ret;
}
static void __exit hw_break_module_exit(void)
{
unregister_wide_hw_breakpoint(sample_hbp);
printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
}
module_init(hw_break_module_init);
module_exit(hw_break_module_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("K.Prasad");
MODULE_DESCRIPTION("ksym breakpoint");
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