samples/hw_breakpoint/data_breakpoint.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
   4  *
   5  * usage: insmod data_breakpoint.ko ksym=<ksym_name>
   6  *
   7  * This file is a kernel module that places a breakpoint over ksym_name kernel
   8  * variable using Hardware Breakpoint register. The corresponding handler which
   9  * prints a backtrace is invoked every time a write operation is performed on
  10  * that variable.
  11  *
  12  * Copyright (C) IBM Corporation, 2009
  13  *
  14  * Author: K.Prasad <prasad@linux.vnet.ibm.com>
  15  */
  16 #include <linux/module.h>       /* Needed by all modules */
  17 #include <linux/kernel.h>       /* Needed for KERN_INFO */
  18 #include <linux/init.h>         /* Needed for the macros */
  19 #include <linux/kallsyms.h>
  20
  21 #include <linux/perf_event.h>
  22 #include <linux/hw_breakpoint.h>
  23
  24 static struct perf_event * __percpu *sample_hbp;
  25
  26 static char ksym_name[KSYM_NAME_LEN] = "jiffies";
  27 module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
  28 MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
  29                         " write operations on the kernel symbol");
  30
  31 static void sample_hbp_handler(struct perf_event *bp,
  32                                struct perf_sample_data *data,
  33                                struct pt_regs *regs)
  34 {
  35         printk(KERN_INFO "%s value is changed\n", ksym_name);
  36         dump_stack();
  37         printk(KERN_INFO "Dump stack from sample_hbp_handler\n");
  38 }
  39
  40 static int __init hw_break_module_init(void)
  41 {
  42         int ret;
  43         struct perf_event_attr attr;
  44         void *addr = __symbol_get(ksym_name);
  45
  46         if (!addr)
  47                 return -ENXIO;
  48
  49         hw_breakpoint_init(&attr);
  50         attr.bp_addr = (unsigned long)addr;
  51         attr.bp_len = HW_BREAKPOINT_LEN_4;
  52         attr.bp_type = HW_BREAKPOINT_W;
  53
  54         sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
  55         if (IS_ERR((void __force *)sample_hbp)) {
  56                 ret = PTR_ERR((void __force *)sample_hbp);
  57                 goto fail;
  58         }
  59
  60         printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
  61
  62         return 0;
  63
  64 fail:
  65         printk(KERN_INFO "Breakpoint registration failed\n");
  66
  67         return ret;
  68 }
  69
  70 static void __exit hw_break_module_exit(void)
  71 {
  72         unregister_wide_hw_breakpoint(sample_hbp);
  73 #ifdef CONFIG_MODULE_UNLOAD
  74         __symbol_put(ksym_name);
  75 #endif
  76         printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
  77 }
  78
  79 module_init(hw_break_module_init);
  80 module_exit(hw_break_module_exit);
  81
  82 MODULE_LICENSE("GPL");
  83 MODULE_AUTHOR("K.Prasad");
  84 MODULE_DESCRIPTION("ksym breakpoint");