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Linux/samples/hw_breakpoint/data_breakpoint.c

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  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 every time 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 * __percpu *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,
 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, NULL);
 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 
 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");
 91 

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