kgdboc.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Based on the same principle as kgdboe using the NETPOLL api, this
  4 * driver uses a console polling api to implement a gdb serial inteface
  5 * which is multiplexed on a console port.
  6 *
  7 * Maintainer: Jason Wessel <jason.wessel@windriver.com>
  8 *
  9 * 2007-2008 (c) Jason Wessel - Wind River Systems, Inc.
 10 */
 11
 12#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 13
 14#include <linux/kernel.h>
 15#include <linux/ctype.h>
 16#include <linux/kgdb.h>
 17#include <linux/kdb.h>
 18#include <linux/tty.h>
 19#include <linux/console.h>
 20#include <linux/vt_kern.h>
 21#include <linux/input.h>
 22#include <linux/irq_work.h>
 23#include <linux/module.h>
 24#include <linux/platform_device.h>
 25#include <linux/serial_core.h>
 26
 27#define MAX_CONFIG_LEN		40
 28
 29static struct kgdb_io		kgdboc_io_ops;
 30
 31/* -1 = init not run yet, 0 = unconfigured, 1 = configured. */
 32static int configured		= -1;
 33static DEFINE_MUTEX(config_mutex);
 34
 35static char config[MAX_CONFIG_LEN];
 36static struct kparam_string kps = {
 37	.string			= config,
 38	.maxlen			= MAX_CONFIG_LEN,
 39};
 40
 41static int kgdboc_use_kms;  /* 1 if we use kernel mode switching */
 42static struct tty_driver	*kgdb_tty_driver;
 43static int			kgdb_tty_line;
 44
 45static struct platform_device *kgdboc_pdev;
 46
 47#if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
 48static struct kgdb_io		kgdboc_earlycon_io_ops;
 49static int                      (*earlycon_orig_exit)(struct console *con);
 50#endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
 51
 52/*
 53 * When we leave the debug trap handler we need to reset the keyboard status
 54 * (since the original keyboard state gets partially clobbered by kdb use of
 55 * the keyboard).
 56 *
 57 * The path to deliver the reset is somewhat circuitous.
 58 *
 59 * To deliver the reset we register an input handler, reset the keyboard and
 60 * then deregister the input handler. However, to get this done right, we do
 61 * have to carefully manage the calling context because we can only register
 62 * input handlers from task context.
 63 *
 64 * In particular we need to trigger the action from the debug trap handler with
 65 * all its NMI and/or NMI-like oddities. To solve this the kgdboc trap exit code
 66 * (the "post_exception" callback) uses irq_work_queue(), which is NMI-safe, to
 67 * schedule a callback from a hardirq context. From there we have to defer the
 68 * work again, this time using schedule_work(), to get a callback using the
 69 * system workqueue, which runs in task context.
 70 */
 71#ifdef CONFIG_KDB_KEYBOARD
 72static int kgdboc_reset_connect(struct input_handler *handler,
 73				struct input_dev *dev,
 74				const struct input_device_id *id)
 75{
 76	input_reset_device(dev);
 77
 78	/* Return an error - we do not want to bind, just to reset */
 79	return -ENODEV;
 80}
 81
 82static void kgdboc_reset_disconnect(struct input_handle *handle)
 83{
 84	/* We do not expect anyone to actually bind to us */
 85	BUG();
 86}
 87
 88static const struct input_device_id kgdboc_reset_ids[] = {
 89	{
 90		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
 91		.evbit = { BIT_MASK(EV_KEY) },
 92	},
 93	{ }
 94};
 95
 96static struct input_handler kgdboc_reset_handler = {
 97	.connect	= kgdboc_reset_connect,
 98	.disconnect	= kgdboc_reset_disconnect,
 99	.name		= "kgdboc_reset",
100	.id_table	= kgdboc_reset_ids,
101};
102
103static DEFINE_MUTEX(kgdboc_reset_mutex);
104
105static void kgdboc_restore_input_helper(struct work_struct *dummy)
106{
107	/*
108	 * We need to take a mutex to prevent several instances of
109	 * this work running on different CPUs so they don't try
110	 * to register again already registered handler.
111	 */
112	mutex_lock(&kgdboc_reset_mutex);
113
114	if (input_register_handler(&kgdboc_reset_handler) == 0)
115		input_unregister_handler(&kgdboc_reset_handler);
116
117	mutex_unlock(&kgdboc_reset_mutex);
118}
119
120static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
121
122static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
123{
124	schedule_work(&kgdboc_restore_input_work);
125}
126
127static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
128
129static void kgdboc_restore_input(void)
130{
131	if (likely(system_state == SYSTEM_RUNNING))
132		irq_work_queue(&kgdboc_restore_input_irq_work);
133}
134
135static int kgdboc_register_kbd(char **cptr)
136{
137	if (strncmp(*cptr, "kbd", 3) == 0 ||
138		strncmp(*cptr, "kdb", 3) == 0) {
139		if (kdb_poll_idx < KDB_POLL_FUNC_MAX) {
140			kdb_poll_funcs[kdb_poll_idx] = kdb_get_kbd_char;
141			kdb_poll_idx++;
142			if (cptr[0][3] == ',')
143				*cptr += 4;
144			else
145				return 1;
146		}
147	}
148	return 0;
149}
150
151static void kgdboc_unregister_kbd(void)
152{
153	int i;
154
155	for (i = 0; i < kdb_poll_idx; i++) {
156		if (kdb_poll_funcs[i] == kdb_get_kbd_char) {
157			kdb_poll_idx--;
158			kdb_poll_funcs[i] = kdb_poll_funcs[kdb_poll_idx];
159			kdb_poll_funcs[kdb_poll_idx] = NULL;
160			i--;
161		}
162	}
163	irq_work_sync(&kgdboc_restore_input_irq_work);
164	flush_work(&kgdboc_restore_input_work);
165}
166#else /* ! CONFIG_KDB_KEYBOARD */
167#define kgdboc_register_kbd(x) 0
168#define kgdboc_unregister_kbd()
169#define kgdboc_restore_input()
170#endif /* ! CONFIG_KDB_KEYBOARD */
171
172#if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
173static void cleanup_earlycon(void)
174{
175	if (kgdboc_earlycon_io_ops.cons)
176		kgdb_unregister_io_module(&kgdboc_earlycon_io_ops);
177}
178#else /* !IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
179static inline void cleanup_earlycon(void) { }
180#endif /* !IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
181
182static void cleanup_kgdboc(void)
183{
184	cleanup_earlycon();
185
186	if (configured != 1)
187		return;
188
189	kgdboc_unregister_kbd();
190	kgdb_unregister_io_module(&kgdboc_io_ops);
191}
192
193static int configure_kgdboc(void)
194{
195	struct tty_driver *p;
196	int tty_line = 0;
197	int err = -ENODEV;
198	char *cptr = config;
199	struct console *cons;
200	int cookie;
201
202	if (!strlen(config) || isspace(config[0])) {
203		err = 0;
204		goto noconfig;
205	}
206
207	kgdboc_io_ops.cons = NULL;
208	kgdb_tty_driver = NULL;
209
210	kgdboc_use_kms = 0;
211	if (strncmp(cptr, "kms,", 4) == 0) {
212		cptr += 4;
213		kgdboc_use_kms = 1;
214	}
215
216	if (kgdboc_register_kbd(&cptr))
217		goto do_register;
218
219	p = tty_find_polling_driver(cptr, &tty_line);
220	if (!p)
221		goto noconfig;
222
223	/*
224	 * Take console_lock to serialize device() callback with
225	 * other console operations. For example, fg_console is
226	 * modified under console_lock when switching vt.
227	 */
228	console_lock();
229
230	cookie = console_srcu_read_lock();
231	for_each_console_srcu(cons) {
232		int idx;
233		if (cons->device && cons->device(cons, &idx) == p &&
234		    idx == tty_line) {
235			kgdboc_io_ops.cons = cons;
236			break;
237		}
238	}
239	console_srcu_read_unlock(cookie);
240
241	console_unlock();
242
243	kgdb_tty_driver = p;
244	kgdb_tty_line = tty_line;
245
246do_register:
247	err = kgdb_register_io_module(&kgdboc_io_ops);
248	if (err)
249		goto noconfig;
250
251	configured = 1;
252
253	return 0;
254
255noconfig:
256	kgdboc_unregister_kbd();
257	configured = 0;
258
259	return err;
260}
261
262static int kgdboc_probe(struct platform_device *pdev)
263{
264	int ret = 0;
265
266	mutex_lock(&config_mutex);
267	if (configured != 1) {
268		ret = configure_kgdboc();
269
270		/* Convert "no device" to "defer" so we'll keep trying */
271		if (ret == -ENODEV)
272			ret = -EPROBE_DEFER;
273	}
274	mutex_unlock(&config_mutex);
275
276	return ret;
277}
278
279static struct platform_driver kgdboc_platform_driver = {
280	.probe = kgdboc_probe,
281	.driver = {
282		.name = "kgdboc",
283		.suppress_bind_attrs = true,
284	},
285};
286
287static int __init init_kgdboc(void)
288{
289	int ret;
290
291	/*
292	 * kgdboc is a little bit of an odd "platform_driver".  It can be
293	 * up and running long before the platform_driver object is
294	 * created and thus doesn't actually store anything in it.  There's
295	 * only one instance of kgdb so anything is stored as global state.
296	 * The platform_driver is only created so that we can leverage the
297	 * kernel's mechanisms (like -EPROBE_DEFER) to call us when our
298	 * underlying tty is ready.  Here we init our platform driver and
299	 * then create the single kgdboc instance.
300	 */
301	ret = platform_driver_register(&kgdboc_platform_driver);
302	if (ret)
303		return ret;
304
305	kgdboc_pdev = platform_device_alloc("kgdboc", PLATFORM_DEVID_NONE);
306	if (!kgdboc_pdev) {
307		ret = -ENOMEM;
308		goto err_did_register;
309	}
310
311	ret = platform_device_add(kgdboc_pdev);
312	if (!ret)
313		return 0;
314
315	platform_device_put(kgdboc_pdev);
316
317err_did_register:
318	platform_driver_unregister(&kgdboc_platform_driver);
319	return ret;
320}
321
322static void exit_kgdboc(void)
323{
324	mutex_lock(&config_mutex);
325	cleanup_kgdboc();
326	mutex_unlock(&config_mutex);
327
328	platform_device_unregister(kgdboc_pdev);
329	platform_driver_unregister(&kgdboc_platform_driver);
330}
331
332static int kgdboc_get_char(void)
333{
334	if (!kgdb_tty_driver)
335		return -1;
336	return kgdb_tty_driver->ops->poll_get_char(kgdb_tty_driver,
337						kgdb_tty_line);
338}
339
340static void kgdboc_put_char(u8 chr)
341{
342	if (!kgdb_tty_driver)
343		return;
344	kgdb_tty_driver->ops->poll_put_char(kgdb_tty_driver,
345					kgdb_tty_line, chr);
346}
347
348static int param_set_kgdboc_var(const char *kmessage,
349				const struct kernel_param *kp)
350{
351	size_t len = strlen(kmessage);
352	int ret = 0;
353
354	if (len >= MAX_CONFIG_LEN) {
355		pr_err("config string too long\n");
356		return -ENOSPC;
357	}
358
359	if (kgdb_connected) {
360		pr_err("Cannot reconfigure while KGDB is connected.\n");
361		return -EBUSY;
362	}
363
364	mutex_lock(&config_mutex);
365
366	strcpy(config, kmessage);
367	/* Chop out \n char as a result of echo */
368	if (len && config[len - 1] == '\n')
369		config[len - 1] = '\0';
370
371	if (configured == 1)
372		cleanup_kgdboc();
373
374	/*
375	 * Configure with the new params as long as init already ran.
376	 * Note that we can get called before init if someone loads us
377	 * with "modprobe kgdboc kgdboc=..." or if they happen to use
378	 * the odd syntax of "kgdboc.kgdboc=..." on the kernel command.
379	 */
380	if (configured >= 0)
381		ret = configure_kgdboc();
382
383	/*
384	 * If we couldn't configure then clear out the config.  Note that
385	 * specifying an invalid config on the kernel command line vs.
386	 * through sysfs have slightly different behaviors.  If we fail
387	 * to configure what was specified on the kernel command line
388	 * we'll leave it in the 'config' and return -EPROBE_DEFER from
389	 * our probe.  When specified through sysfs userspace is
390	 * responsible for loading the tty driver before setting up.
391	 */
392	if (ret)
393		config[0] = '\0';
394
395	mutex_unlock(&config_mutex);
396
397	return ret;
398}
399
400static int dbg_restore_graphics;
401
402static void kgdboc_pre_exp_handler(void)
403{
404	if (!dbg_restore_graphics && kgdboc_use_kms) {
405		dbg_restore_graphics = 1;
406		con_debug_enter(vc_cons[fg_console].d);
407	}
408	/* Increment the module count when the debugger is active */
409	if (!kgdb_connected)
410		try_module_get(THIS_MODULE);
411}
412
413static void kgdboc_post_exp_handler(void)
414{
415	/* decrement the module count when the debugger detaches */
416	if (!kgdb_connected)
417		module_put(THIS_MODULE);
418	if (kgdboc_use_kms && dbg_restore_graphics) {
419		dbg_restore_graphics = 0;
420		con_debug_leave();
421	}
422	kgdboc_restore_input();
423}
424
425static struct kgdb_io kgdboc_io_ops = {
426	.name			= "kgdboc",
427	.read_char		= kgdboc_get_char,
428	.write_char		= kgdboc_put_char,
429	.pre_exception		= kgdboc_pre_exp_handler,
430	.post_exception		= kgdboc_post_exp_handler,
431};
432
433#if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
434static int kgdboc_option_setup(char *opt)
435{
436	if (!opt) {
437		pr_err("config string not provided\n");
438		return 1;
439	}
440
441	if (strlen(opt) >= MAX_CONFIG_LEN) {
442		pr_err("config string too long\n");
443		return 1;
444	}
445	strcpy(config, opt);
446
447	return 1;
448}
449
450__setup("kgdboc=", kgdboc_option_setup);
451
452
453/* This is only available if kgdboc is a built in for early debugging */
454static int __init kgdboc_early_init(char *opt)
455{
456	kgdboc_option_setup(opt);
457	configure_kgdboc();
458	return 0;
459}
460
461early_param("ekgdboc", kgdboc_early_init);
462
463static int kgdboc_earlycon_get_char(void)
464{
465	char c;
466
467	if (!kgdboc_earlycon_io_ops.cons->read(kgdboc_earlycon_io_ops.cons,
468					       &c, 1))
469		return NO_POLL_CHAR;
470
471	return c;
472}
473
474static void kgdboc_earlycon_put_char(u8 chr)
475{
476	kgdboc_earlycon_io_ops.cons->write(kgdboc_earlycon_io_ops.cons, &chr,
477					   1);
478}
479
480static void kgdboc_earlycon_pre_exp_handler(void)
481{
482	struct console *con;
483	static bool already_warned;
484	int cookie;
485
486	if (already_warned)
487		return;
488
489	/*
490	 * When the first normal console comes up the kernel will take all
491	 * the boot consoles out of the list.  Really, we should stop using
492	 * the boot console when it does that but until a TTY is registered
493	 * we have no other choice so we keep using it.  Since not all
494	 * serial drivers might be OK with this, print a warning once per
495	 * boot if we detect this case.
496	 */
497	cookie = console_srcu_read_lock();
498	for_each_console_srcu(con) {
499		if (con == kgdboc_earlycon_io_ops.cons)
500			break;
501	}
502	console_srcu_read_unlock(cookie);
503	if (con)
504		return;
505
506	already_warned = true;
507	pr_warn("kgdboc_earlycon is still using bootconsole\n");
508}
509
510static int kgdboc_earlycon_deferred_exit(struct console *con)
511{
512	/*
513	 * If we get here it means the boot console is going away but we
514	 * don't yet have a suitable replacement.  Don't pass through to
515	 * the original exit routine.  We'll call it later in our deinit()
516	 * function.  For now, restore the original exit() function pointer
517	 * as a sentinal that we've hit this point.
518	 */
519	con->exit = earlycon_orig_exit;
520
521	return 0;
522}
523
524static void kgdboc_earlycon_deinit(void)
525{
526	if (!kgdboc_earlycon_io_ops.cons)
527		return;
528
529	if (kgdboc_earlycon_io_ops.cons->exit == kgdboc_earlycon_deferred_exit)
530		/*
531		 * kgdboc_earlycon is exiting but original boot console exit
532		 * was never called (AKA kgdboc_earlycon_deferred_exit()
533		 * didn't ever run).  Undo our trap.
534		 */
535		kgdboc_earlycon_io_ops.cons->exit = earlycon_orig_exit;
536	else if (kgdboc_earlycon_io_ops.cons->exit)
537		/*
538		 * We skipped calling the exit() routine so we could try to
539		 * keep using the boot console even after it went away.  We're
540		 * finally done so call the function now.
541		 */
542		kgdboc_earlycon_io_ops.cons->exit(kgdboc_earlycon_io_ops.cons);
543
544	kgdboc_earlycon_io_ops.cons = NULL;
545}
546
547static struct kgdb_io kgdboc_earlycon_io_ops = {
548	.name			= "kgdboc_earlycon",
549	.read_char		= kgdboc_earlycon_get_char,
550	.write_char		= kgdboc_earlycon_put_char,
551	.pre_exception		= kgdboc_earlycon_pre_exp_handler,
552	.deinit			= kgdboc_earlycon_deinit,
553};
554
555#define MAX_CONSOLE_NAME_LEN (sizeof((struct console *) 0)->name)
556static char kgdboc_earlycon_param[MAX_CONSOLE_NAME_LEN] __initdata;
557static bool kgdboc_earlycon_late_enable __initdata;
558
559static int __init kgdboc_earlycon_init(char *opt)
560{
561	struct console *con;
562
563	kdb_init(KDB_INIT_EARLY);
564
565	/*
566	 * Look for a matching console, or if the name was left blank just
567	 * pick the first one we find.
568	 */
569
570	/*
571	 * Hold the console_list_lock to guarantee that no consoles are
572	 * unregistered until the kgdboc_earlycon setup is complete.
573	 * Trapping the exit() callback relies on exit() not being
574	 * called until the trap is setup. This also allows safe
575	 * traversal of the console list and race-free reading of @flags.
576	 */
577	console_list_lock();
578	for_each_console(con) {
579		if (con->write && con->read &&
580		    (!opt || !opt[0] || strcmp(con->name, opt) == 0))
581			break;
582	}
583
584	if (!con) {
585		/*
586		 * Both earlycon and kgdboc_earlycon are initialized during
587		 * early parameter parsing. We cannot guarantee earlycon gets
588		 * in first and, in any case, on ACPI systems earlycon may
589		 * defer its own initialization (usually to somewhere within
590		 * setup_arch() ). To cope with either of these situations
591		 * we can defer our own initialization to a little later in
592		 * the boot.
593		 */
594		if (!kgdboc_earlycon_late_enable) {
595			pr_info("No suitable earlycon yet, will try later\n");
596			if (opt)
597				strscpy(kgdboc_earlycon_param, opt,
598					sizeof(kgdboc_earlycon_param));
599			kgdboc_earlycon_late_enable = true;
600		} else {
601			pr_info("Couldn't find kgdb earlycon\n");
602		}
603		goto unlock;
604	}
605
606	kgdboc_earlycon_io_ops.cons = con;
607	pr_info("Going to register kgdb with earlycon '%s'\n", con->name);
608	if (kgdb_register_io_module(&kgdboc_earlycon_io_ops) != 0) {
609		kgdboc_earlycon_io_ops.cons = NULL;
610		pr_info("Failed to register kgdb with earlycon\n");
611	} else {
612		/* Trap exit so we can keep earlycon longer if needed. */
613		earlycon_orig_exit = con->exit;
614		con->exit = kgdboc_earlycon_deferred_exit;
615	}
616
617unlock:
618	console_list_unlock();
619
620	/* Non-zero means malformed option so we always return zero */
621	return 0;
622}
623
624early_param("kgdboc_earlycon", kgdboc_earlycon_init);
625
626/*
627 * This is only intended for the late adoption of an early console.
628 *
629 * It is not a reliable way to adopt regular consoles because we can not
630 * control what order console initcalls are made and, in any case, many
631 * regular consoles are registered much later in the boot process than
632 * the console initcalls!
633 */
634static int __init kgdboc_earlycon_late_init(void)
635{
636	if (kgdboc_earlycon_late_enable)
637		kgdboc_earlycon_init(kgdboc_earlycon_param);
638	return 0;
639}
640console_initcall(kgdboc_earlycon_late_init);
641
642#endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
643
644module_init(init_kgdboc);
645module_exit(exit_kgdboc);
646module_param_call(kgdboc, param_set_kgdboc_var, param_get_string, &kps, 0644);
647MODULE_PARM_DESC(kgdboc, "<serial_device>[,baud]");
648MODULE_DESCRIPTION("KGDB Console TTY Driver");
649MODULE_LICENSE("GPL");