[linux-2.6-block.git] / samples / hw_breakpoint / data_breakpoint.c

// 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((void __force *)sample_hbp)) {
		ret = PTR_ERR((void __force *)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");
Commit	Line	Data
1a59d1b8	1	// SPDX-License-Identifier: GPL-2.0-or-later
43203993 P	2	/*
	3	* data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
	4	*
43203993 P	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
25985edc	9	* prints a backtrace is invoked every time a write operation is performed on
43203993 P	10	* that variable.
	11	*
	12	* Copyright (C) IBM Corporation, 2009
ba6909b7 P	13	*
ba6909b7 P	14	* Author: K.Prasad <prasad@linux.vnet.ibm.com>
43203993 P	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 */
f60d24d2	19	#include <linux/kallsyms.h>
43203993	20
f60d24d2 FW	21	#include <linux/perf_event.h>
f60d24d2 FW	22	#include <linux/hw_breakpoint.h>
43203993	23
4b49df65	24	static struct perf_event * __percpu *sample_hbp;
43203993	25
d8a84d33	26	static char ksym_name[KSYM_NAME_LEN] = "jiffies";
43203993 P	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
a8b0ca17	31	static void sample_hbp_handler(struct perf_event *bp,
b326e956 FW	32	struct perf_sample_data *data,
b326e956 FW	33	struct pt_regs *regs)
43203993 P	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;
b326e956	43	struct perf_event_attr attr;
d8a84d33 WD	44	void *addr = __symbol_get(ksym_name);
	45
	46	if (!addr)
	47	return -ENXIO;
43203993	48
b326e956	49	hw_breakpoint_init(&attr);
d8a84d33	50	attr.bp_addr = (unsigned long)addr;
dd1853c3	51	attr.bp_len = HW_BREAKPOINT_LEN_4;
4800314e	52	attr.bp_type = HW_BREAKPOINT_W;
43203993	53
4dc0da86	54	sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
44ee6358 TH	55	if (IS_ERR((void __force *)sample_hbp)) {
44ee6358 TH	56	ret = PTR_ERR((void __force *)sample_hbp);
f60d24d2	57	goto fail;
f60d24d2	58	}
43203993	59
f60d24d2	60	printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name);
43203993 P	61
43203993 P	62	return 0;
f60d24d2 FW	63
	64	fail:
	65	printk(KERN_INFO "Breakpoint registration failed\n");
	66
	67	return ret;
43203993 P	68	}
	69
	70	static void __exit hw_break_module_exit(void)
	71	{
f60d24d2	72	unregister_wide_hw_breakpoint(sample_hbp);
b9080468	73	#ifdef CONFIG_MODULE_UNLOAD
910e230d	74	__symbol_put(ksym_name);
b9080468	75	#endif
43203993 P	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");