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 * Author: K.Prasad <prasad@linux.vnet.ibm.com> 28 */ 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> 33 34#include <linux/perf_event.h> 35#include <linux/hw_breakpoint.h> 36 37struct perf_event * __percpu *sample_hbp; 38 39static char ksym_name[KSYM_NAME_LEN] = "pid_max"; 40module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO); 41MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any" 42 " write operations on the kernel symbol"); 43 44static void sample_hbp_handler(struct perf_event *bp, int nmi, 45 struct perf_sample_data *data, 46 struct pt_regs *regs) 47{ 48 printk(KERN_INFO "%s value is changed\n", ksym_name); 49 dump_stack(); 50 printk(KERN_INFO "Dump stack from sample_hbp_handler\n"); 51} 52 53static int __init hw_break_module_init(void) 54{ 55 int ret; 56 struct perf_event_attr attr; 57 58 hw_breakpoint_init(&attr); 59 attr.bp_addr = kallsyms_lookup_name(ksym_name); 60 attr.bp_len = HW_BREAKPOINT_LEN_4; 61 attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R; 62 63 sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler); 64 if (IS_ERR((void __force *)sample_hbp)) { 65 ret = PTR_ERR((void __force *)sample_hbp); 66 goto fail; 67 } 68 69 printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name); 70 71 return 0; 72 73fail: 74 printk(KERN_INFO "Breakpoint registration failed\n"); 75 76 return ret; 77} 78 79static void __exit hw_break_module_exit(void) 80{ 81 unregister_wide_hw_breakpoint(sample_hbp); 82 printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name); 83} 84 85module_init(hw_break_module_init); 86module_exit(hw_break_module_exit); 87 88MODULE_LICENSE("GPL"); 89MODULE_AUTHOR("K.Prasad"); 90MODULE_DESCRIPTION("ksym breakpoint"); 91