Commit 43203993 authored by K.Prasad's avatar K.Prasad Committed by Frederic Weisbecker

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: 's avatarK.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
parent 17f557e5
......@@ -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
# 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/
obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o
/*
* 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");
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