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
23static struct fprobe sample_probe;
24static unsigned long nhit;
25
26static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
27module_param_string(symbol, symbol, sizeof(symbol), 0644);
28MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern.");
29
30static char nosymbol[MAX_SYMBOL_LEN] = "";
31module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
32MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern.");
33
34static bool stackdump = true;
35module_param(stackdump, bool, 0644);
36MODULE_PARM_DESC(stackdump, "Enable stackdump.");
37
38static bool use_trace = false;
39module_param(use_trace, bool, 0644);
40MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging.");
41
42static 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
51static int sample_entry_handler(struct fprobe *fp, unsigned long ip,
52				unsigned long ret_ip,
53				struct pt_regs *regs, void *data)
54{
55	if (use_trace)
56		/*
57		 * This is just an example, no kernel code should call
58		 * trace_printk() except when actively debugging.
59		 */
60		trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
61	else
62		pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
63	nhit++;
64	if (stackdump)
65		show_backtrace();
66	return 0;
67}
68
69static void sample_exit_handler(struct fprobe *fp, unsigned long ip,
70				unsigned long ret_ip, struct pt_regs *regs,
71				void *data)
72{
73	unsigned long rip = ret_ip;
74
75	if (use_trace)
76		/*
77		 * This is just an example, no kernel code should call
78		 * trace_printk() except when actively debugging.
79		 */
80		trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
81			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
82	else
83		pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
84			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
85	nhit++;
86	if (stackdump)
87		show_backtrace();
88}
89
90static int __init fprobe_init(void)
91{
92	char *p, *symbuf = NULL;
93	const char **syms;
94	int ret, count, i;
95
96	sample_probe.entry_handler = sample_entry_handler;
97	sample_probe.exit_handler = sample_exit_handler;
98
99	if (strchr(symbol, '*')) {
100		/* filter based fprobe */
101		ret = register_fprobe(&sample_probe, symbol,
102				      nosymbol[0] == '\0' ? NULL : nosymbol);
103		goto out;
104	} else if (!strchr(symbol, ',')) {
105		symbuf = symbol;
106		ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
107		goto out;
108	}
109
110	/* Comma separated symbols */
111	symbuf = kstrdup(symbol, GFP_KERNEL);
112	if (!symbuf)
113		return -ENOMEM;
114	p = symbuf;
115	count = 1;
116	while ((p = strchr(++p, ',')) != NULL)
117		count++;
118
119	pr_info("%d symbols found\n", count);
120
121	syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
122	if (!syms) {
123		kfree(symbuf);
124		return -ENOMEM;
125	}
126
127	p = symbuf;
128	for (i = 0; i < count; i++)
129		syms[i] = strsep(&p, ",");
130
131	ret = register_fprobe_syms(&sample_probe, syms, count);
132	kfree(syms);
133	kfree(symbuf);
134out:
135	if (ret < 0)
136		pr_err("register_fprobe failed, returned %d\n", ret);
137	else
138		pr_info("Planted fprobe at %s\n", symbol);
139
140	return ret;
141}
142
143static void __exit fprobe_exit(void)
144{
145	unregister_fprobe(&sample_probe);
146
147	pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
148		symbol, nhit, sample_probe.nmissed);
149}
150
151module_init(fprobe_init)
152module_exit(fprobe_exit)
153MODULE_LICENSE("GPL");
154