// SPDX-License-Identifier: GPL-2.0-only/* * Here's a sample kernel module showing the use of fprobe to dump a * stack trace and selected registers when kernel_clone() is called. * * For more information on theory of operation of kprobes, see * Documentation/trace/kprobes.rst * * You will see the trace data in /var/log/messages and on the console * whenever kernel_clone() is invoked to create a new process. */ #define pr_fmt(fmt) "%s: " fmt, __func__ #include <linux/kernel.h>#include <linux/module.h>#include <linux/fprobe.h>#include <linux/sched/debug.h>#include <linux/slab.h> #define BACKTRACE_DEPTH 16#define MAX_SYMBOL_LEN 4096static struct fprobe sample_probe;static unsigned long nhit; static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";module_param_string(symbol, symbol, sizeof(symbol), 0644);MODULE_PARM_DESC(symbol, "Probed symbol(s), given by comma separated symbols or a wildcard pattern."); static char nosymbol[MAX_SYMBOL_LEN] = "";module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);MODULE_PARM_DESC(nosymbol, "Not-probed symbols, given by a wildcard pattern."); static bool stackdump = true;module_param(stackdump, bool, 0644);MODULE_PARM_DESC(stackdump, "Enable stackdump."); static bool use_trace = false;module_param(use_trace, bool, 0644);MODULE_PARM_DESC(use_trace, "Use trace_printk instead of printk. This is only for debugging."); static void show_backtrace(void){	unsigned long stacks[BACKTRACE_DEPTH];	unsigned int len; 	len = stack_trace_save(stacks, BACKTRACE_DEPTH, 2);	stack_trace_print(stacks, len, 24);} static int sample_entry_handler(struct fprobe *fp, unsigned long ip,				unsigned long ret_ip,				struct pt_regs *regs, void *data){	if (use_trace)		/*		 * This is just an example, no kernel code should call		 * trace_printk() except when actively debugging.		 */		trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);	else		pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);	nhit++;	if (stackdump)		show_backtrace();	return 0;} static void sample_exit_handler(struct fprobe *fp, unsigned long ip,				unsigned long ret_ip, struct pt_regs *regs,				void *data){	unsigned long rip = ret_ip; 	if (use_trace)		/*		 * This is just an example, no kernel code should call		 * trace_printk() except when actively debugging.		 */		trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",			(void *)ip, (void *)ip, (void *)rip, (void *)rip);	else		pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",			(void *)ip, (void *)ip, (void *)rip, (void *)rip);	nhit++;	if (stackdump)		show_backtrace();} static int __init fprobe_init(void){	char *p, *symbuf = NULL;	const char **syms;	int ret, count, i; 	sample_probe.entry_handler = sample_entry_handler;	sample_probe.exit_handler = sample_exit_handler; 	if (strchr(symbol, '*')) {		/* filter based fprobe */		ret = register_fprobe(&sample_probe, symbol,				      nosymbol[0] == '\0' ? NULL : nosymbol);		goto out;	} else if (!strchr(symbol, ',')) {		symbuf = symbol;		ret = register_fprobe_syms(&sample_probe, (const char **)&symbuf, 1);		goto out;	} 	/* Comma separated symbols */	symbuf = kstrdup(symbol, GFP_KERNEL);	if (!symbuf)		return -ENOMEM;	p = symbuf;	count = 1;	while ((p = strchr(++p, ',')) != NULL)		count++; 	pr_info("%d symbols found\n", count); 	syms = kcalloc(count, sizeof(char *), GFP_KERNEL);	if (!syms) {		kfree(symbuf);		return -ENOMEM;	} 	p = symbuf;	for (i = 0; i < count; i++)		syms[i] = strsep(&p, ","); 	ret = register_fprobe_syms(&sample_probe, syms, count);	kfree(syms);	kfree(symbuf);out:	if (ret < 0)		pr_err("register_fprobe failed, returned %d\n", ret);	else		pr_info("Planted fprobe at %s\n", symbol); 	return ret;} static void __exit fprobe_exit(void){	unregister_fprobe(&sample_probe); 	pr_info("fprobe at %s unregistered. %ld times hit, %ld times missed\n",		symbol, nhit, sample_probe.nmissed);} module_init(fprobe_init)module_exit(fprobe_exit)MODULE_DESCRIPTION("sample kernel module showing the use of fprobe");MODULE_LICENSE("GPL");