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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 | * |
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> |
22 | #include <linux/hw_breakpoint.h> | |
43203993 | 23 | |
44ee6358 | 24 | struct perf_event * __percpu *sample_hbp; |
43203993 | 25 | |
d8a84d33 | 26 | static char ksym_name[KSYM_NAME_LEN] = "jiffies"; |
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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, |
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)) { |
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); |
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61 | |
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); |
910e230d | 73 | __symbol_put(ksym_name); |
43203993 P |
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"); |