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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 |
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10 | * that variable. |
11 | * | |
12 | * Copyright (C) IBM Corporation, 2009 | |
ba6909b7 P |
13 | * |
14 | * Author: K.Prasad <prasad@linux.vnet.ibm.com> | |
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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; |
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25 | |
26 | static char ksym_name[KSYM_NAME_LEN] = "pid_max"; | |
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; |
43203993 | 44 | |
b326e956 | 45 | hw_breakpoint_init(&attr); |
dd1853c3 FW |
46 | attr.bp_addr = kallsyms_lookup_name(ksym_name); |
47 | attr.bp_len = HW_BREAKPOINT_LEN_4; | |
48 | attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R; | |
43203993 | 49 | |
4dc0da86 | 50 | sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL); |
44ee6358 TH |
51 | if (IS_ERR((void __force *)sample_hbp)) { |
52 | ret = PTR_ERR((void __force *)sample_hbp); | |
f60d24d2 | 53 | goto fail; |
f60d24d2 | 54 | } |
43203993 | 55 | |
f60d24d2 | 56 | printk(KERN_INFO "HW Breakpoint for %s write installed\n", ksym_name); |
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57 | |
58 | return 0; | |
f60d24d2 FW |
59 | |
60 | fail: | |
61 | printk(KERN_INFO "Breakpoint registration failed\n"); | |
62 | ||
63 | return ret; | |
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64 | } |
65 | ||
66 | static void __exit hw_break_module_exit(void) | |
67 | { | |
f60d24d2 | 68 | unregister_wide_hw_breakpoint(sample_hbp); |
43203993 P |
69 | printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name); |
70 | } | |
71 | ||
72 | module_init(hw_break_module_init); | |
73 | module_exit(hw_break_module_exit); | |
74 | ||
75 | MODULE_LICENSE("GPL"); | |
76 | MODULE_AUTHOR("K.Prasad"); | |
77 | MODULE_DESCRIPTION("ksym breakpoint"); |