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
sample_hbp_handler(struct perf_event * bp,struct perf_sample_data * data,struct pt_regs * regs)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
hw_break_module_init(void)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
hw_break_module_exit(void)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");
85