summaryrefslogtreecommitdiffstats
path: root/samples/fprobe/fprobe_example.c
blob: 01ee6c8c8382921d253e0a130b8a05df3c60ebc1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Here's a sample kernel module showing the use of fprobe to dump a
 * stack trace and selected registers when kernel_clone() is called.
 *
 * For more information on theory of operation of kprobes, see
 * Documentation/trace/kprobes.rst
 *
 * You will see the trace data in /var/log/messages and on the console
 * whenever kernel_clone() is invoked to create a new process.
 */

#define pr_fmt(fmt) "%s: " fmt, __func__

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fprobe.h>
#include <linux/sched/debug.h>
#include <linux/slab.h>

#define BACKTRACE_DEPTH 16
#define MAX_SYMBOL_LEN 4096
struct fprobe sample_probe;
static unsigned long nhit;

static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
module_param_string(symbol, symbol, sizeof(symbol), 0644);
static char nosymbol[MAX_SYMBOL_LEN] = "";
module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
static bool stackdump = true;
module_param(stackdump, bool, 0644);
static bool use_trace = false;
module_param(use_trace, bool, 0644);

static void show_backtrace(void)
{
	unsigned long stacks[BACKTRACE_DEPTH];
	unsigned int len;

	len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);
	stack_trace_print(stacks, len, 24);
}

static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
{
	if (use_trace)
		/*
		 * This is just an example, no kernel code should call
		 * trace_printk() except when actively debugging.
		 */
		trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
	else
		pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
	nhit++;
	if (stackdump)
		show_backtrace();
}

static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
{
	unsigned long rip = instruction_pointer(regs);

	if (use_trace)
		/*
		 * This is just an example, no kernel code should call
		 * trace_printk() except when actively debugging.
		 */
		trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
	else
		pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
	nhit++;
	if (stackdump)
		show_backtrace();
}

static int __init fprobe_init(void)
{
	char *p, *symbuf = NULL;
	const char **syms;
	int ret, count, i;

	sample_probe.entry_handler = sample_entry_handler;
	sample_probe.exit_handler = sample_exit_handler;

	if (strchr(symbol, '*')) {
		/* filter based fprobe */
		ret = register_fprobe(&sample_probe, symbol,
				      nosymbol[0] == '\0' ? NULL : nosymbol);
		goto out;
	} else if (!strchr(symbol, ',')) {
		symbuf = symbol;
		ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
		goto out;
	}

	/* Comma separated symbols */
	symbuf = kstrdup(symbol, GFP_KERNEL);
	if (!symbuf)
		return -ENOMEM;
	p = symbuf;
	count = 1;
	while ((p = strchr(++p, ',')) != NULL)
		count++;

	pr_info("%d symbols found\n", count);

	syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
	if (!syms) {
		kfree(symbuf);
		return -ENOMEM;
	}

	p = symbuf;
	for (i = 0; i < count; i++)
		syms[i] = strsep(&p, ",");

	ret = register_fprobe_syms(&sample_probe, syms, count);
	kfree(syms);
	kfree(symbuf);
out:
	if (ret < 0)
		pr_err("register_fprobe failed, returned %d\n", ret);
	else
		pr_info("Planted fprobe at %s\n", symbol);

	return ret;
}

static void __exit fprobe_exit(void)
{
	unregister_fprobe(&sample_probe);

	pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
		symbol, nhit, sample_probe.nmissed);
}

module_init(fprobe_init)
module_exit(fprobe_exit)
MODULE_LICENSE("GPL");