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 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 symbol_put(ksym_name); 74 printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name); 75 } 76 77 module_init(hw_break_module_init); 78 module_exit(hw_break_module_exit); 79 80 MODULE_LICENSE("GPL"); 81 MODULE_AUTHOR("K.Prasad"); 82 MODULE_DESCRIPTION("ksym breakpoint"); 83