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
23struct fprobe sample_probe;
24
25static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
26module_param_string(symbol, symbol, sizeof(symbol), 0644);
27static char nosymbol[MAX_SYMBOL_LEN] = "";
28module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
29static bool stackdump = true;
30module_param(stackdump, bool, 0644);
31
32static 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
41static 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
48static 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
58static 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);
102out:
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
111static void __exit fprobe_exit(void)
112{
113 unregister_fprobe(&sample_probe);
114
115 pr_info("fprobe at %s unregistered\n", symbol);
116}
117
118module_init(fprobe_init)
119module_exit(fprobe_exit)
120MODULE_LICENSE("GPL");