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
23 struct fprobe sample_probe;
24 
25 static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
26 module_param_string(symbol, symbol, sizeof(symbol), 0644);
27 static char nosymbol[MAX_SYMBOL_LEN] = "";
28 module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
29 static bool stackdump = true;
30 module_param(stackdump, bool, 0644);
31 
32 static void show_backtrace(void)
33 {
34 	unsigned long stacks[BACKTRACE_DEPTH];
35 	unsigned int len;
36 
37 	len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);
38 	stack_trace_print(stacks, len, 24);
39 }
40 
41 static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
42 {
43 	pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
44 	if (stackdump)
45 		show_backtrace();
46 }
47 
48 static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
49 {
50 	unsigned long rip = instruction_pointer(regs);
51 
52 	pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
53 		(void *)ip, (void *)ip, (void *)rip, (void *)rip);
54 	if (stackdump)
55 		show_backtrace();
56 }
57 
58 static int __init fprobe_init(void)
59 {
60 	char *p, *symbuf = NULL;
61 	const char **syms;
62 	int ret, count, i;
63 
64 	sample_probe.entry_handler = sample_entry_handler;
65 	sample_probe.exit_handler = sample_exit_handler;
66 
67 	if (strchr(symbol, '*')) {
68 		/* filter based fprobe */
69 		ret = register_fprobe(&sample_probe, symbol,
70 				      nosymbol[0] == '\0' ? NULL : nosymbol);
71 		goto out;
72 	} else if (!strchr(symbol, ',')) {
73 		symbuf = symbol;
74 		ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
75 		goto out;
76 	}
77 
78 	/* Comma separated symbols */
79 	symbuf = kstrdup(symbol, GFP_KERNEL);
80 	if (!symbuf)
81 		return -ENOMEM;
82 	p = symbuf;
83 	count = 1;
84 	while ((p = strchr(++p, ',')) != NULL)
85 		count++;
86 
87 	pr_info("%d symbols found\n", count);
88 
89 	syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
90 	if (!syms) {
91 		kfree(symbuf);
92 		return -ENOMEM;
93 	}
94 
95 	p = symbuf;
96 	for (i = 0; i < count; i++)
97 		syms[i] = strsep(&p, ",");
98 
99 	ret = register_fprobe_syms(&sample_probe, syms, count);
100 	kfree(syms);
101 	kfree(symbuf);
102 out:
103 	if (ret < 0)
104 		pr_err("register_fprobe failed, returned %d\n", ret);
105 	else
106 		pr_info("Planted fprobe at %s\n", symbol);
107 
108 	return ret;
109 }
110 
111 static void __exit fprobe_exit(void)
112 {
113 	unregister_fprobe(&sample_probe);
114 
115 	pr_info("fprobe at %s unregistered\n", symbol);
116 }
117 
118 module_init(fprobe_init)
119 module_exit(fprobe_exit)
120 MODULE_LICENSE("GPL");
121