Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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 struct pt_regs *regs, void *data)
53{
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++;
63 if (stackdump)
64 show_backtrace();
65 return 0;
66}
67
68static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs,
69 void *data)
70{
71 unsigned long rip = instruction_pointer(regs);
72
73 if (use_trace)
74 /*
75 * This is just an example, no kernel code should call
76 * trace_printk() except when actively debugging.
77 */
78 trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
79 (void *)ip, (void *)ip, (void *)rip, (void *)rip);
80 else
81 pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
82 (void *)ip, (void *)ip, (void *)rip, (void *)rip);
83 nhit++;
84 if (stackdump)
85 show_backtrace();
86}
87
88static int __init fprobe_init(void)
89{
90 char *p, *symbuf = NULL;
91 const char **syms;
92 int ret, count, i;
93
94 sample_probe.entry_handler = sample_entry_handler;
95 sample_probe.exit_handler = sample_exit_handler;
96
97 if (strchr(symbol, '*')) {
98 /* filter based fprobe */
99 ret = register_fprobe(&sample_probe, symbol,
100 nosymbol[0] == '\0' ? NULL : nosymbol);
101 goto out;
102 } else if (!strchr(symbol, ',')) {
103 symbuf = symbol;
104 ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
105 goto out;
106 }
107
108 /* Comma separated symbols */
109 symbuf = kstrdup(symbol, GFP_KERNEL);
110 if (!symbuf)
111 return -ENOMEM;
112 p = symbuf;
113 count = 1;
114 while ((p = strchr(++p, ',')) != NULL)
115 count++;
116
117 pr_info("%d symbols found\n", count);
118
119 syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
120 if (!syms) {
121 kfree(symbuf);
122 return -ENOMEM;
123 }
124
125 p = symbuf;
126 for (i = 0; i < count; i++)
127 syms[i] = strsep(&p, ",");
128
129 ret = register_fprobe_syms(&sample_probe, syms, count);
130 kfree(syms);
131 kfree(symbuf);
132out:
133 if (ret < 0)
134 pr_err("register_fprobe failed, returned %d\n", ret);
135 else
136 pr_info("Planted fprobe at %s\n", symbol);
137
138 return ret;
139}
140
141static void __exit fprobe_exit(void)
142{
143 unregister_fprobe(&sample_probe);
144
145 pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
146 symbol, nhit, sample_probe.nmissed);
147}
148
149module_init(fprobe_init)
150module_exit(fprobe_exit)
151MODULE_LICENSE("GPL");