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Commit 43203993 authored by K.Prasad's avatar K.Prasad Committed by Frederic Weisbecker
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hw-breakpoints: sample HW breakpoint over kernel data address 



This patch introduces a sample kernel module to demonstrate the use of Hardware
Breakpoint feature. It places a breakpoint over the kernel variable 'pid_max'
to monitor all write operations and emits a function-backtrace when done.

Signed-off-by: default avatarK.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent 17f557e5

samples/Kconfig

+6 −0
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@@ -45,5 +45,11 @@ config SAMPLE_KRETPROBES 
	default m

	depends on SAMPLE_KPROBES && KRETPROBES



config SAMPLE_HW_BREAKPOINT

	tristate "Build kernel hardware breakpoint examples -- loadable module only"

	depends on HAVE_HW_BREAKPOINT && m

	help

	  This builds kernel hardware breakpoint example modules.



endif # SAMPLES

samples/Makefile

+2 −1
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# Makefile for Linux samples code



obj-$(CONFIG_SAMPLES)	+= markers/ kobject/ kprobes/ tracepoints/ trace_events/
 
obj-$(CONFIG_SAMPLES)	+= markers/ kobject/ kprobes/ tracepoints/ \

			trace_events/ hw_breakpoint/

samples/hw_breakpoint/Makefile

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+1 −0
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obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o

samples/hw_breakpoint/data_breakpoint.c

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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

 */

#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 <asm/hw_breakpoint.h>



struct hw_breakpoint 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");



void sample_hbp_handler(struct hw_breakpoint *temp, struct pt_regs

								*temp_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;



#ifdef CONFIG_X86

	sample_hbp.info.name = ksym_name;

	sample_hbp.info.type = HW_BREAKPOINT_WRITE;

	sample_hbp.info.len = HW_BREAKPOINT_LEN_4;

#endif /* CONFIG_X86 */



	sample_hbp.triggered = (void *)sample_hbp_handler;



	ret = register_kernel_hw_breakpoint(&sample_hbp);



	if (ret < 0) {

		printk(KERN_INFO "Breakpoint registration failed\n");

		return ret;

	} else

		printk(KERN_INFO "HW Breakpoint for %s write installed\n",

								ksym_name);



	return 0;

}



static void __exit hw_break_module_exit(void)

{

	unregister_kernel_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");