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6ee64cc3 MH |
1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* | |
3 | * Here's a sample kernel module showing the use of fprobe to dump a | |
4 | * stack trace and selected registers when kernel_clone() is called. | |
5 | * | |
6 | * For more information on theory of operation of kprobes, see | |
7 | * Documentation/trace/kprobes.rst | |
8 | * | |
9 | * You will see the trace data in /var/log/messages and on the console | |
10 | * whenever kernel_clone() is invoked to create a new process. | |
11 | */ | |
12 | ||
13 | #define pr_fmt(fmt) "%s: " fmt, __func__ | |
14 | ||
15 | #include <linux/kernel.h> | |
16 | #include <linux/module.h> | |
17 | #include <linux/fprobe.h> | |
18 | #include <linux/sched/debug.h> | |
19 | #include <linux/slab.h> | |
20 | ||
21 | #define BACKTRACE_DEPTH 16 | |
22 | #define MAX_SYMBOL_LEN 4096 | |
e3655dfa | 23 | static struct fprobe sample_probe; |
c88dbbcd | 24 | static unsigned long nhit; |
6ee64cc3 MH |
25 | |
26 | static char symbol[MAX_SYMBOL_LEN] = "kernel_clone"; | |
27 | module_param_string(symbol, symbol, sizeof(symbol), 0644); | |
179a93f7 MHG |
28 | MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern."); |
29 | ||
6ee64cc3 MH |
30 | static char nosymbol[MAX_SYMBOL_LEN] = ""; |
31 | module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644); | |
179a93f7 MHG |
32 | MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern."); |
33 | ||
6ee64cc3 MH |
34 | static bool stackdump = true; |
35 | module_param(stackdump, bool, 0644); | |
179a93f7 MHG |
36 | MODULE_PARM_DESC(stackdump, "Enable stackdump."); |
37 | ||
c88dbbcd MHG |
38 | static bool use_trace = false; |
39 | module_param(use_trace, bool, 0644); | |
179a93f7 | 40 | MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging."); |
6ee64cc3 MH |
41 | |
42 | static void show_backtrace(void) | |
43 | { | |
44 | unsigned long stacks[BACKTRACE_DEPTH]; | |
45 | unsigned int len; | |
46 | ||
47 | len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2); | |
48 | stack_trace_print(stacks, len, 24); | |
49 | } | |
50 | ||
76d0de57 MHG |
51 | static void sample_entry_handler(struct fprobe *fp, unsigned long ip, |
52 | struct pt_regs *regs, void *data) | |
6ee64cc3 | 53 | { |
c88dbbcd MHG |
54 | if (use_trace) |
55 | /* | |
56 | * This is just an example, no kernel code should call | |
57 | * trace_printk() except when actively debugging. | |
58 | */ | |
59 | trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); | |
60 | else | |
61 | pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip); | |
62 | nhit++; | |
6ee64cc3 MH |
63 | if (stackdump) |
64 | show_backtrace(); | |
65 | } | |
66 | ||
76d0de57 MHG |
67 | static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs, |
68 | void *data) | |
6ee64cc3 MH |
69 | { |
70 | unsigned long rip = instruction_pointer(regs); | |
71 | ||
c88dbbcd MHG |
72 | if (use_trace) |
73 | /* | |
74 | * This is just an example, no kernel code should call | |
75 | * trace_printk() except when actively debugging. | |
76 | */ | |
77 | trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", | |
78 | (void *)ip, (void *)ip, (void *)rip, (void *)rip); | |
79 | else | |
80 | pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n", | |
81 | (void *)ip, (void *)ip, (void *)rip, (void *)rip); | |
82 | nhit++; | |
6ee64cc3 MH |
83 | if (stackdump) |
84 | show_backtrace(); | |
85 | } | |
86 | ||
87 | static int __init fprobe_init(void) | |
88 | { | |
89 | char *p, *symbuf = NULL; | |
90 | const char **syms; | |
91 | int ret, count, i; | |
92 | ||
93 | sample_probe.entry_handler = sample_entry_handler; | |
94 | sample_probe.exit_handler = sample_exit_handler; | |
95 | ||
96 | if (strchr(symbol, '*')) { | |
97 | /* filter based fprobe */ | |
98 | ret = register_fprobe(&sample_probe, symbol, | |
99 | nosymbol[0] == '\0' ? NULL : nosymbol); | |
100 | goto out; | |
101 | } else if (!strchr(symbol, ',')) { | |
102 | symbuf = symbol; | |
103 | ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1); | |
104 | goto out; | |
105 | } | |
106 | ||
107 | /* Comma separated symbols */ | |
108 | symbuf = kstrdup(symbol, GFP_KERNEL); | |
109 | if (!symbuf) | |
110 | return -ENOMEM; | |
111 | p = symbuf; | |
112 | count = 1; | |
113 | while ((p = strchr(++p, ',')) != NULL) | |
114 | count++; | |
115 | ||
116 | pr_info("%d symbols found\n", count); | |
117 | ||
118 | syms = kcalloc(count, sizeof(char *), GFP_KERNEL); | |
119 | if (!syms) { | |
120 | kfree(symbuf); | |
121 | return -ENOMEM; | |
122 | } | |
123 | ||
124 | p = symbuf; | |
125 | for (i = 0; i < count; i++) | |
126 | syms[i] = strsep(&p, ","); | |
127 | ||
128 | ret = register_fprobe_syms(&sample_probe, syms, count); | |
129 | kfree(syms); | |
130 | kfree(symbuf); | |
131 | out: | |
132 | if (ret < 0) | |
133 | pr_err("register_fprobe failed, returned %d\n", ret); | |
134 | else | |
135 | pr_info("Planted fprobe at %s\n", symbol); | |
136 | ||
137 | return ret; | |
138 | } | |
139 | ||
140 | static void __exit fprobe_exit(void) | |
141 | { | |
142 | unregister_fprobe(&sample_probe); | |
143 | ||
c88dbbcd MHG |
144 | pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n", |
145 | symbol, nhit, sample_probe.nmissed); | |
6ee64cc3 MH |
146 | } |
147 | ||
148 | module_init(fprobe_init) | |
149 | module_exit(fprobe_exit) | |
150 | MODULE_LICENSE("GPL"); |