samples/hw_breakpoint/data_breakpoint.c

   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
  37 struct perf_event **sample_hbp;
  38
  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");
  43
  44 static 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
  53 static 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(sample_hbp)) {
  65                 ret = PTR_ERR(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
  73 fail:
  74         printk(KERN_INFO "Breakpoint registration failed\n");
  75
  76         return ret;
  77 }
  78
  79 static 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
  85 module_init(hw_break_module_init);
  86 module_exit(hw_break_module_exit);
  87
  88 MODULE_LICENSE("GPL");
  89 MODULE_AUTHOR("K.Prasad");
  90 MODULE_DESCRIPTION("ksym breakpoint");