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_DESCRIPTION("sample kernel module showing the use of fprobe");
154MODULE_LICENSE("GPL");