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;
24static unsigned long nhit;
25
26static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
27module_param_string(symbol, symbol, sizeof(symbol), 0644);
28static char nosymbol[MAX_SYMBOL_LEN] = "";
29module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
30static bool stackdump = true;
31module_param(stackdump, bool, 0644);
32static bool use_trace = false;
33module_param(use_trace, bool, 0644);
34
35static void show_backtrace(void)
36{
37 unsigned long stacks[BACKTRACE_DEPTH];
38 unsigned int len;
39
40 len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);
41 stack_trace_print(stacks, len, 24);
42}
43
44static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
45{
46 if (use_trace)
47 /*
48 * This is just an example, no kernel code should call
49 * trace_printk() except when actively debugging.
50 */
51 trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
52 else
53 pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
54 nhit++;
55 if (stackdump)
56 show_backtrace();
57}
58
59static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
60{
61 unsigned long rip = instruction_pointer(regs);
62
63 if (use_trace)
64 /*
65 * This is just an example, no kernel code should call
66 * trace_printk() except when actively debugging.
67 */
68 trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
69 (void *)ip, (void *)ip, (void *)rip, (void *)rip);
70 else
71 pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
72 (void *)ip, (void *)ip, (void *)rip, (void *)rip);
73 nhit++;
74 if (stackdump)
75 show_backtrace();
76}
77
78static int __init fprobe_init(void)
79{
80 char *p, *symbuf = NULL;
81 const char **syms;
82 int ret, count, i;
83
84 sample_probe.entry_handler = sample_entry_handler;
85 sample_probe.exit_handler = sample_exit_handler;
86
87 if (strchr(symbol, '*')) {
88 /* filter based fprobe */
89 ret = register_fprobe(&sample_probe, symbol,
90 nosymbol[0] == '\0' ? NULL : nosymbol);
91 goto out;
92 } else if (!strchr(symbol, ',')) {
93 symbuf = symbol;
94 ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
95 goto out;
96 }
97
98 /* Comma separated symbols */
99 symbuf = kstrdup(symbol, GFP_KERNEL);
100 if (!symbuf)
101 return -ENOMEM;
102 p = symbuf;
103 count = 1;
104 while ((p = strchr(++p, ',')) != NULL)
105 count++;
106
107 pr_info("%d symbols found\n", count);
108
109 syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
110 if (!syms) {
111 kfree(symbuf);
112 return -ENOMEM;
113 }
114
115 p = symbuf;
116 for (i = 0; i < count; i++)
117 syms[i] = strsep(&p, ",");
118
119 ret = register_fprobe_syms(&sample_probe, syms, count);
120 kfree(syms);
121 kfree(symbuf);
122out:
123 if (ret < 0)
124 pr_err("register_fprobe failed, returned %d\n", ret);
125 else
126 pr_info("Planted fprobe at %s\n", symbol);
127
128 return ret;
129}
130
131static void __exit fprobe_exit(void)
132{
133 unregister_fprobe(&sample_probe);
134
135 pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
136 symbol, nhit, sample_probe.nmissed);
137}
138
139module_init(fprobe_init)
140module_exit(fprobe_exit)
141MODULE_LICENSE("GPL");