// SPDX-License-Identifier: GPL-2.0-or-later/* * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address * * usage: insmod data_breakpoint.ko ksym=<ksym_name> * * This file is a kernel module that places a breakpoint over ksym_name kernel * variable using Hardware Breakpoint register. The corresponding handler which * prints a backtrace is invoked every time a write operation is performed on * that variable. * * Copyright (C) IBM Corporation, 2009 * * Author: K.Prasad <prasad@linux.vnet.ibm.com> */#include <linux/module.h>	/* Needed by all modules */#include <linux/kernel.h>	/* Needed for KERN_INFO */#include <linux/init.h>		/* Needed for the macros */#include <linux/kallsyms.h> #include <linux/perf_event.h>#include <linux/hw_breakpoint.h> static struct perf_event * __percpu *sample_hbp; static char ksym_name[KSYM_NAME_LEN] = "jiffies";module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"			" write operations on the kernel symbol"); static void sample_hbp_handler(struct perf_event *bp,			       struct perf_sample_data *data,			       struct pt_regs *regs){	printk(KERN_INFO "%s value is changed\n", ksym_name);	dump_stack();	printk(KERN_INFO "Dump stack from sample_hbp_handler\n");} static int __init hw_break_module_init(void){	int ret;	struct perf_event_attr attr;	void *addr = __symbol_get(ksym_name); 	if (!addr)		return -ENXIO; 	hw_breakpoint_init(&attr);	attr.bp_addr = (unsigned long)addr;	attr.bp_len = HW_BREAKPOINT_LEN_4;	attr.bp_type = HW_BREAKPOINT_W; 	sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);	if (IS_ERR_PCPU(sample_hbp)) {		ret = PTR_ERR_PCPU(sample_hbp);		goto fail;	} 	printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name); 	return 0; fail:	printk(KERN_INFO "Breakpoint registration failed\n"); 	return ret;} static void __exit hw_break_module_exit(void){	unregister_wide_hw_breakpoint(sample_hbp);#ifdef CONFIG_MODULE_UNLOAD	__symbol_put(ksym_name);#endif	printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);} module_init(hw_break_module_init);module_exit(hw_break_module_exit); MODULE_LICENSE("GPL");MODULE_AUTHOR("K.Prasad");MODULE_DESCRIPTION("ksym breakpoint");