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  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 void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
 52{
 53	if (use_trace)
 54		/*
 55		 * This is just an example, no kernel code should call
 56		 * trace_printk() except when actively debugging.
 57		 */
 58		trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
 59	else
 60		pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
 61	nhit++;
 62	if (stackdump)
 63		show_backtrace();
 64}
 65
 66static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
 67{
 68	unsigned long rip = instruction_pointer(regs);
 69
 70	if (use_trace)
 71		/*
 72		 * This is just an example, no kernel code should call
 73		 * trace_printk() except when actively debugging.
 74		 */
 75		trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
 76			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
 77	else
 78		pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
 79			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
 80	nhit++;
 81	if (stackdump)
 82		show_backtrace();
 83}
 84
 85static int __init fprobe_init(void)
 86{
 87	char *p, *symbuf = NULL;
 88	const char **syms;
 89	int ret, count, i;
 90
 91	sample_probe.entry_handler = sample_entry_handler;
 92	sample_probe.exit_handler = sample_exit_handler;
 93
 94	if (strchr(symbol, '*')) {
 95		/* filter based fprobe */
 96		ret = register_fprobe(&sample_probe, symbol,
 97				      nosymbol[0] == '\0' ? NULL : nosymbol);
 98		goto out;
 99	} else if (!strchr(symbol, ',')) {
100		symbuf = symbol;
101		ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);
102		goto out;
103	}
104
105	/* Comma separated symbols */
106	symbuf = kstrdup(symbol, GFP_KERNEL);
107	if (!symbuf)
108		return -ENOMEM;
109	p = symbuf;
110	count = 1;
111	while ((p = strchr(++p, ',')) != NULL)
112		count++;
113
114	pr_info("%d symbols found\n", count);
115
116	syms = kcalloc(count, sizeof(char *), GFP_KERNEL);
117	if (!syms) {
118		kfree(symbuf);
119		return -ENOMEM;
120	}
121
122	p = symbuf;
123	for (i = 0; i < count; i++)
124		syms[i] = strsep(&p, ",");
125
126	ret = register_fprobe_syms(&sample_probe, syms, count);
127	kfree(syms);
128	kfree(symbuf);
129out:
130	if (ret < 0)
131		pr_err("register_fprobe failed, returned %d\n", ret);
132	else
133		pr_info("Planted fprobe at %s\n", symbol);
134
135	return ret;
136}
137
138static void __exit fprobe_exit(void)
139{
140	unregister_fprobe(&sample_probe);
141
142	pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",
143		symbol, nhit, sample_probe.nmissed);
144}
145
146module_init(fprobe_init)
147module_exit(fprobe_exit)
148MODULE_LICENSE("GPL");