debug_core.c

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * Kernel Debug Core
   4 *
   5 * Maintainer: Jason Wessel <jason.wessel@windriver.com>
   6 *
   7 * Copyright (C) 2000-2001 VERITAS Software Corporation.
   8 * Copyright (C) 2002-2004 Timesys Corporation
   9 * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
  10 * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
  11 * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
  12 * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
  13 * Copyright (C) 2005-2009 Wind River Systems, Inc.
  14 * Copyright (C) 2007 MontaVista Software, Inc.
  15 * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  16 *
  17 * Contributors at various stages not listed above:
  18 *  Jason Wessel ( jason.wessel@windriver.com )
  19 *  George Anzinger <george@mvista.com>
  20 *  Anurekh Saxena (anurekh.saxena@timesys.com)
  21 *  Lake Stevens Instrument Division (Glenn Engel)
  22 *  Jim Kingdon, Cygnus Support.
  23 *
  24 * Original KGDB stub: David Grothe <dave@gcom.com>,
  25 * Tigran Aivazian <tigran@sco.com>
  26 */
  27
  28#define pr_fmt(fmt) "KGDB: " fmt
  29
  30#include <linux/pid_namespace.h>
  31#include <linux/clocksource.h>
  32#include <linux/serial_core.h>
  33#include <linux/interrupt.h>
  34#include <linux/spinlock.h>
  35#include <linux/console.h>
  36#include <linux/threads.h>
  37#include <linux/uaccess.h>
  38#include <linux/kernel.h>
  39#include <linux/module.h>
  40#include <linux/ptrace.h>
  41#include <linux/string.h>
  42#include <linux/delay.h>
  43#include <linux/sched.h>
  44#include <linux/sysrq.h>
  45#include <linux/reboot.h>
  46#include <linux/init.h>
  47#include <linux/kgdb.h>
  48#include <linux/kdb.h>
  49#include <linux/nmi.h>
  50#include <linux/pid.h>
  51#include <linux/smp.h>
  52#include <linux/mm.h>
  53#include <linux/rcupdate.h>
  54#include <linux/irq.h>
  55#include <linux/security.h>
  56
  57#include <asm/cacheflush.h>
  58#include <asm/byteorder.h>
  59#include <linux/atomic.h>
  60
  61#include "debug_core.h"
  62
  63static int kgdb_break_asap;
  64
  65struct debuggerinfo_struct kgdb_info[NR_CPUS];
  66
  67/* kgdb_connected - Is a host GDB connected to us? */
  68int				kgdb_connected;
  69EXPORT_SYMBOL_GPL(kgdb_connected);
  70
  71/* All the KGDB handlers are installed */
  72int			kgdb_io_module_registered;
  73
  74/* Guard for recursive entry */
  75static int			exception_level;
  76
  77struct kgdb_io		*dbg_io_ops;
  78static DEFINE_SPINLOCK(kgdb_registration_lock);
  79
  80/* Action for the reboot notifier, a global allow kdb to change it */
  81static int kgdbreboot;
  82/* kgdb console driver is loaded */
  83static int kgdb_con_registered;
  84/* determine if kgdb console output should be used */
  85static int kgdb_use_con;
  86/* Flag for alternate operations for early debugging */
  87bool dbg_is_early = true;
  88/* Next cpu to become the master debug core */
  89int dbg_switch_cpu;
  90
  91/* Use kdb or gdbserver mode */
  92int dbg_kdb_mode = 1;
  93
  94module_param(kgdb_use_con, int, 0644);
  95module_param(kgdbreboot, int, 0644);
  96
  97/*
  98 * Holds information about breakpoints in a kernel. These breakpoints are
  99 * added and removed by gdb.
 100 */
 101static struct kgdb_bkpt		kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 102	[0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 103};
 104
 105/*
 106 * The CPU# of the active CPU, or -1 if none:
 107 */
 108atomic_t			kgdb_active = ATOMIC_INIT(-1);
 109EXPORT_SYMBOL_GPL(kgdb_active);
 110static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 111static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 112
 113/*
 114 * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 115 * bootup code (which might not have percpu set up yet):
 116 */
 117static atomic_t			masters_in_kgdb;
 118static atomic_t			slaves_in_kgdb;
 119atomic_t			kgdb_setting_breakpoint;
 120
 121struct task_struct		*kgdb_usethread;
 122struct task_struct		*kgdb_contthread;
 123
 124int				kgdb_single_step;
 125static pid_t			kgdb_sstep_pid;
 126
 127/* to keep track of the CPU which is doing the single stepping*/
 128atomic_t			kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 129
 130/*
 131 * If you are debugging a problem where roundup (the collection of
 132 * all other CPUs) is a problem [this should be extremely rare],
 133 * then use the nokgdbroundup option to avoid roundup. In that case
 134 * the other CPUs might interfere with your debugging context, so
 135 * use this with care:
 136 */
 137static int kgdb_do_roundup = 1;
 138
 139static int __init opt_nokgdbroundup(char *str)
 140{
 141	kgdb_do_roundup = 0;
 142
 143	return 0;
 144}
 145
 146early_param("nokgdbroundup", opt_nokgdbroundup);
 147
 148/*
 149 * Finally, some KGDB code :-)
 150 */
 151
 152/*
 153 * Weak aliases for breakpoint management,
 154 * can be overridden by architectures when needed:
 155 */
 156int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 157{
 158	int err;
 159
 160	err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
 161				BREAK_INSTR_SIZE);
 162	if (err)
 163		return err;
 164	err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
 165				 arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 166	return err;
 167}
 168NOKPROBE_SYMBOL(kgdb_arch_set_breakpoint);
 169
 170int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 171{
 172	return copy_to_kernel_nofault((char *)bpt->bpt_addr,
 173				  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 174}
 175NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
 176
 177int __weak kgdb_validate_break_address(unsigned long addr)
 178{
 179	struct kgdb_bkpt tmp;
 180	int err;
 181
 182	if (kgdb_within_blocklist(addr))
 183		return -EINVAL;
 184
 185	/* Validate setting the breakpoint and then removing it.  If the
 186	 * remove fails, the kernel needs to emit a bad message because we
 187	 * are deep trouble not being able to put things back the way we
 188	 * found them.
 189	 */
 190	tmp.bpt_addr = addr;
 191	err = kgdb_arch_set_breakpoint(&tmp);
 192	if (err)
 193		return err;
 194	err = kgdb_arch_remove_breakpoint(&tmp);
 195	if (err)
 196		pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 197		       addr);
 198	return err;
 199}
 200
 201unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 202{
 203	return instruction_pointer(regs);
 204}
 205NOKPROBE_SYMBOL(kgdb_arch_pc);
 206
 207int __weak kgdb_arch_init(void)
 208{
 209	return 0;
 210}
 211
 212int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 213{
 214	return 0;
 215}
 216NOKPROBE_SYMBOL(kgdb_skipexception);
 217
 218#ifdef CONFIG_SMP
 219
 220/*
 221 * Default (weak) implementation for kgdb_roundup_cpus
 222 */
 223
 224void __weak kgdb_call_nmi_hook(void *ignored)
 225{
 226	/*
 227	 * NOTE: get_irq_regs() is supposed to get the registers from
 228	 * before the IPI interrupt happened and so is supposed to
 229	 * show where the processor was.  In some situations it's
 230	 * possible we might be called without an IPI, so it might be
 231	 * safer to figure out how to make kgdb_breakpoint() work
 232	 * properly here.
 233	 */
 234	kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 235}
 236NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 237
 238static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
 239	CSD_INIT(kgdb_call_nmi_hook, NULL);
 240
 241void __weak kgdb_roundup_cpus(void)
 242{
 243	call_single_data_t *csd;
 244	int this_cpu = raw_smp_processor_id();
 245	int cpu;
 246	int ret;
 247
 248	for_each_online_cpu(cpu) {
 249		/* No need to roundup ourselves */
 250		if (cpu == this_cpu)
 251			continue;
 252
 253		csd = &per_cpu(kgdb_roundup_csd, cpu);
 254
 255		/*
 256		 * If it didn't round up last time, don't try again
 257		 * since smp_call_function_single_async() will block.
 258		 *
 259		 * If rounding_up is false then we know that the
 260		 * previous call must have at least started and that
 261		 * means smp_call_function_single_async() won't block.
 262		 */
 263		if (kgdb_info[cpu].rounding_up)
 264			continue;
 265		kgdb_info[cpu].rounding_up = true;
 266
 267		ret = smp_call_function_single_async(cpu, csd);
 268		if (ret)
 269			kgdb_info[cpu].rounding_up = false;
 270	}
 271}
 272NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 273
 274#endif
 275
 276/*
 277 * Some architectures need cache flushes when we set/clear a
 278 * breakpoint:
 279 */
 280static void kgdb_flush_swbreak_addr(unsigned long addr)
 281{
 282	if (!CACHE_FLUSH_IS_SAFE)
 283		return;
 284
 285	/* Force flush instruction cache if it was outside the mm */
 286	flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 287}
 288NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
 289
 290/*
 291 * SW breakpoint management:
 292 */
 293int dbg_activate_sw_breakpoints(void)
 294{
 295	int error;
 296	int ret = 0;
 297	int i;
 298
 299	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 300		if (kgdb_break[i].state != BP_SET)
 301			continue;
 302
 303		error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 304		if (error) {
 305			ret = error;
 306			pr_info("BP install failed: %lx\n",
 307				kgdb_break[i].bpt_addr);
 308			continue;
 309		}
 310
 311		kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 312		kgdb_break[i].state = BP_ACTIVE;
 313	}
 314	return ret;
 315}
 316NOKPROBE_SYMBOL(dbg_activate_sw_breakpoints);
 317
 318int dbg_set_sw_break(unsigned long addr)
 319{
 320	int err = kgdb_validate_break_address(addr);
 321	int breakno = -1;
 322	int i;
 323
 324	if (err)
 325		return err;
 326
 327	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 328		if ((kgdb_break[i].state == BP_SET) &&
 329					(kgdb_break[i].bpt_addr == addr))
 330			return -EEXIST;
 331	}
 332	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 333		if (kgdb_break[i].state == BP_REMOVED &&
 334					kgdb_break[i].bpt_addr == addr) {
 335			breakno = i;
 336			break;
 337		}
 338	}
 339
 340	if (breakno == -1) {
 341		for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 342			if (kgdb_break[i].state == BP_UNDEFINED) {
 343				breakno = i;
 344				break;
 345			}
 346		}
 347	}
 348
 349	if (breakno == -1)
 350		return -E2BIG;
 351
 352	kgdb_break[breakno].state = BP_SET;
 353	kgdb_break[breakno].type = BP_BREAKPOINT;
 354	kgdb_break[breakno].bpt_addr = addr;
 355
 356	return 0;
 357}
 358
 359int dbg_deactivate_sw_breakpoints(void)
 360{
 361	int error;
 362	int ret = 0;
 363	int i;
 364
 365	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 366		if (kgdb_break[i].state != BP_ACTIVE)
 367			continue;
 368		error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 369		if (error) {
 370			pr_info("BP remove failed: %lx\n",
 371				kgdb_break[i].bpt_addr);
 372			ret = error;
 373		}
 374
 375		kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 376		kgdb_break[i].state = BP_SET;
 377	}
 378	return ret;
 379}
 380NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
 381
 382int dbg_remove_sw_break(unsigned long addr)
 383{
 384	int i;
 385
 386	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 387		if ((kgdb_break[i].state == BP_SET) &&
 388				(kgdb_break[i].bpt_addr == addr)) {
 389			kgdb_break[i].state = BP_REMOVED;
 390			return 0;
 391		}
 392	}
 393	return -ENOENT;
 394}
 395
 396int kgdb_isremovedbreak(unsigned long addr)
 397{
 398	int i;
 399
 400	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 401		if ((kgdb_break[i].state == BP_REMOVED) &&
 402					(kgdb_break[i].bpt_addr == addr))
 403			return 1;
 404	}
 405	return 0;
 406}
 407
 408int kgdb_has_hit_break(unsigned long addr)
 409{
 410	int i;
 411
 412	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 413		if (kgdb_break[i].state == BP_ACTIVE &&
 414		    kgdb_break[i].bpt_addr == addr)
 415			return 1;
 416	}
 417	return 0;
 418}
 419
 420int dbg_remove_all_break(void)
 421{
 422	int error;
 423	int i;
 424
 425	/* Clear memory breakpoints. */
 426	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 427		if (kgdb_break[i].state != BP_ACTIVE)
 428			goto setundefined;
 429		error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 430		if (error)
 431			pr_err("breakpoint remove failed: %lx\n",
 432			       kgdb_break[i].bpt_addr);
 433setundefined:
 434		kgdb_break[i].state = BP_UNDEFINED;
 435	}
 436
 437	/* Clear hardware breakpoints. */
 438	if (arch_kgdb_ops.remove_all_hw_break)
 439		arch_kgdb_ops.remove_all_hw_break();
 440
 441	return 0;
 442}
 443
 444void kgdb_free_init_mem(void)
 445{
 446	int i;
 447
 448	/* Clear init memory breakpoints. */
 449	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 450		if (init_section_contains((void *)kgdb_break[i].bpt_addr, 0))
 451			kgdb_break[i].state = BP_UNDEFINED;
 452	}
 453}
 454
 455#ifdef CONFIG_KGDB_KDB
 456void kdb_dump_stack_on_cpu(int cpu)
 457{
 458	if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
 459		dump_stack();
 460		return;
 461	}
 462
 463	if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
 464		kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
 465			   cpu);
 466		return;
 467	}
 468
 469	/*
 470	 * In general, architectures don't support dumping the stack of a
 471	 * "running" process that's not the current one.  From the point of
 472	 * view of the Linux, kernel processes that are looping in the kgdb
 473	 * slave loop are still "running".  There's also no API (that actually
 474	 * works across all architectures) that can do a stack crawl based
 475	 * on registers passed as a parameter.
 476	 *
 477	 * Solve this conundrum by asking slave CPUs to do the backtrace
 478	 * themselves.
 479	 */
 480	kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
 481	while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
 482		cpu_relax();
 483}
 484#endif
 485
 486/*
 487 * Return true if there is a valid kgdb I/O module.  Also if no
 488 * debugger is attached a message can be printed to the console about
 489 * waiting for the debugger to attach.
 490 *
 491 * The print_wait argument is only to be true when called from inside
 492 * the core kgdb_handle_exception, because it will wait for the
 493 * debugger to attach.
 494 */
 495static int kgdb_io_ready(int print_wait)
 496{
 497	if (!dbg_io_ops)
 498		return 0;
 499	if (kgdb_connected)
 500		return 1;
 501	if (atomic_read(&kgdb_setting_breakpoint))
 502		return 1;
 503	if (print_wait) {
 504#ifdef CONFIG_KGDB_KDB
 505		if (!dbg_kdb_mode)
 506			pr_crit("waiting... or $3#33 for KDB\n");
 507#else
 508		pr_crit("Waiting for remote debugger\n");
 509#endif
 510	}
 511	return 1;
 512}
 513NOKPROBE_SYMBOL(kgdb_io_ready);
 514
 515static int kgdb_reenter_check(struct kgdb_state *ks)
 516{
 517	unsigned long addr;
 518
 519	if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 520		return 0;
 521
 522	/* Panic on recursive debugger calls: */
 523	exception_level++;
 524	addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 525	dbg_deactivate_sw_breakpoints();
 526
 527	/*
 528	 * If the break point removed ok at the place exception
 529	 * occurred, try to recover and print a warning to the end
 530	 * user because the user planted a breakpoint in a place that
 531	 * KGDB needs in order to function.
 532	 */
 533	if (dbg_remove_sw_break(addr) == 0) {
 534		exception_level = 0;
 535		kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 536		dbg_activate_sw_breakpoints();
 537		pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 538		WARN_ON_ONCE(1);
 539
 540		return 1;
 541	}
 542	dbg_remove_all_break();
 543	kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 544
 545	if (exception_level > 1) {
 546		dump_stack();
 547		kgdb_io_module_registered = false;
 548		panic("Recursive entry to debugger");
 549	}
 550
 551	pr_crit("re-enter exception: ALL breakpoints killed\n");
 552#ifdef CONFIG_KGDB_KDB
 553	/* Allow kdb to debug itself one level */
 554	return 0;
 555#endif
 556	dump_stack();
 557	panic("Recursive entry to debugger");
 558
 559	return 1;
 560}
 561NOKPROBE_SYMBOL(kgdb_reenter_check);
 562
 563static void dbg_touch_watchdogs(void)
 564{
 565	touch_softlockup_watchdog_sync();
 566	clocksource_touch_watchdog();
 567	rcu_cpu_stall_reset();
 568}
 569NOKPROBE_SYMBOL(dbg_touch_watchdogs);
 570
 571static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 572		int exception_state)
 573{
 574	unsigned long flags;
 575	int sstep_tries = 100;
 576	int error;
 577	int cpu;
 578	int trace_on = 0;
 579	int online_cpus = num_online_cpus();
 580	u64 time_left;
 581
 582	kgdb_info[ks->cpu].enter_kgdb++;
 583	kgdb_info[ks->cpu].exception_state |= exception_state;
 584
 585	if (exception_state == DCPU_WANT_MASTER)
 586		atomic_inc(&masters_in_kgdb);
 587	else
 588		atomic_inc(&slaves_in_kgdb);
 589
 590	if (arch_kgdb_ops.disable_hw_break)
 591		arch_kgdb_ops.disable_hw_break(regs);
 592
 593acquirelock:
 594	rcu_read_lock();
 595	/*
 596	 * Interrupts will be restored by the 'trap return' code, except when
 597	 * single stepping.
 598	 */
 599	local_irq_save(flags);
 600
 601	cpu = ks->cpu;
 602	kgdb_info[cpu].debuggerinfo = regs;
 603	kgdb_info[cpu].task = current;
 604	kgdb_info[cpu].ret_state = 0;
 605	kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 606
 607	/* Make sure the above info reaches the primary CPU */
 608	smp_mb();
 609
 610	if (exception_level == 1) {
 611		if (raw_spin_trylock(&dbg_master_lock))
 612			atomic_xchg(&kgdb_active, cpu);
 613		goto cpu_master_loop;
 614	}
 615
 616	/*
 617	 * CPU will loop if it is a slave or request to become a kgdb
 618	 * master cpu and acquire the kgdb_active lock:
 619	 */
 620	while (1) {
 621cpu_loop:
 622		if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 623			kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 624			goto cpu_master_loop;
 625		} else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 626			if (raw_spin_trylock(&dbg_master_lock)) {
 627				atomic_xchg(&kgdb_active, cpu);
 628				break;
 629			}
 630		} else if (kgdb_info[cpu].exception_state & DCPU_WANT_BT) {
 631			dump_stack();
 632			kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
 633		} else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 634			if (!raw_spin_is_locked(&dbg_slave_lock))
 635				goto return_normal;
 636		} else {
 637return_normal:
 638			/* Return to normal operation by executing any
 639			 * hw breakpoint fixup.
 640			 */
 641			if (arch_kgdb_ops.correct_hw_break)
 642				arch_kgdb_ops.correct_hw_break();
 643			if (trace_on)
 644				tracing_on();
 645			kgdb_info[cpu].debuggerinfo = NULL;
 646			kgdb_info[cpu].task = NULL;
 647			kgdb_info[cpu].exception_state &=
 648				~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 649			kgdb_info[cpu].enter_kgdb--;
 650			smp_mb__before_atomic();
 651			atomic_dec(&slaves_in_kgdb);
 652			dbg_touch_watchdogs();
 653			local_irq_restore(flags);
 654			rcu_read_unlock();
 655			return 0;
 656		}
 657		cpu_relax();
 658	}
 659
 660	/*
 661	 * For single stepping, try to only enter on the processor
 662	 * that was single stepping.  To guard against a deadlock, the
 663	 * kernel will only try for the value of sstep_tries before
 664	 * giving up and continuing on.
 665	 */
 666	if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 667	    (kgdb_info[cpu].task &&
 668	     kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 669		atomic_set(&kgdb_active, -1);
 670		raw_spin_unlock(&dbg_master_lock);
 671		dbg_touch_watchdogs();
 672		local_irq_restore(flags);
 673		rcu_read_unlock();
 674
 675		goto acquirelock;
 676	}
 677
 678	if (!kgdb_io_ready(1)) {
 679		kgdb_info[cpu].ret_state = 1;
 680		goto kgdb_restore; /* No I/O connection, resume the system */
 681	}
 682
 683	/*
 684	 * Don't enter if we have hit a removed breakpoint.
 685	 */
 686	if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 687		goto kgdb_restore;
 688
 689	atomic_inc(&ignore_console_lock_warning);
 690
 691	/* Call the I/O driver's pre_exception routine */
 692	if (dbg_io_ops->pre_exception)
 693		dbg_io_ops->pre_exception();
 694
 695	/*
 696	 * Get the passive CPU lock which will hold all the non-primary
 697	 * CPU in a spin state while the debugger is active
 698	 */
 699	if (!kgdb_single_step)
 700		raw_spin_lock(&dbg_slave_lock);
 701
 702#ifdef CONFIG_SMP
 703	/* If send_ready set, slaves are already waiting */
 704	if (ks->send_ready)
 705		atomic_set(ks->send_ready, 1);
 706
 707	/* Signal the other CPUs to enter kgdb_wait() */
 708	else if ((!kgdb_single_step) && kgdb_do_roundup)
 709		kgdb_roundup_cpus();
 710#endif
 711
 712	/*
 713	 * Wait for the other CPUs to be notified and be waiting for us:
 714	 */
 715	time_left = MSEC_PER_SEC;
 716	while (kgdb_do_roundup && --time_left &&
 717	       (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 718		   online_cpus)
 719		udelay(1000);
 720	if (!time_left)
 721		pr_crit("Timed out waiting for secondary CPUs.\n");
 722
 723	/*
 724	 * At this point the primary processor is completely
 725	 * in the debugger and all secondary CPUs are quiescent
 726	 */
 727	dbg_deactivate_sw_breakpoints();
 728	kgdb_single_step = 0;
 729	kgdb_contthread = current;
 730	exception_level = 0;
 731	trace_on = tracing_is_on();
 732	if (trace_on)
 733		tracing_off();
 734
 735	while (1) {
 736cpu_master_loop:
 737		if (dbg_kdb_mode) {
 738			kgdb_connected = 1;
 739			error = kdb_stub(ks);
 740			if (error == -1)
 741				continue;
 742			kgdb_connected = 0;
 743		} else {
 744			/*
 745			 * This is a brutal way to interfere with the debugger
 746			 * and prevent gdb being used to poke at kernel memory.
 747			 * This could cause trouble if lockdown is applied when
 748			 * there is already an active gdb session. For now the
 749			 * answer is simply "don't do that". Typically lockdown
 750			 * *will* be applied before the debug core gets started
 751			 * so only developers using kgdb for fairly advanced
 752			 * early kernel debug can be biten by this. Hopefully
 753			 * they are sophisticated enough to take care of
 754			 * themselves, especially with help from the lockdown
 755			 * message printed on the console!
 756			 */
 757			if (security_locked_down(LOCKDOWN_DBG_WRITE_KERNEL)) {
 758				if (IS_ENABLED(CONFIG_KGDB_KDB)) {
 759					/* Switch back to kdb if possible... */
 760					dbg_kdb_mode = 1;
 761					continue;
 762				} else {
 763					/* ... otherwise just bail */
 764					break;
 765				}
 766			}
 767			error = gdb_serial_stub(ks);
 768		}
 769
 770		if (error == DBG_PASS_EVENT) {
 771			dbg_kdb_mode = !dbg_kdb_mode;
 772		} else if (error == DBG_SWITCH_CPU_EVENT) {
 773			kgdb_info[dbg_switch_cpu].exception_state |=
 774				DCPU_NEXT_MASTER;
 775			goto cpu_loop;
 776		} else {
 777			kgdb_info[cpu].ret_state = error;
 778			break;
 779		}
 780	}
 781
 782	dbg_activate_sw_breakpoints();
 783
 784	/* Call the I/O driver's post_exception routine */
 785	if (dbg_io_ops->post_exception)
 786		dbg_io_ops->post_exception();
 787
 788	atomic_dec(&ignore_console_lock_warning);
 789
 790	if (!kgdb_single_step) {
 791		raw_spin_unlock(&dbg_slave_lock);
 792		/* Wait till all the CPUs have quit from the debugger. */
 793		while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 794			cpu_relax();
 795	}
 796
 797kgdb_restore:
 798	if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 799		int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 800		if (kgdb_info[sstep_cpu].task)
 801			kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 802		else
 803			kgdb_sstep_pid = 0;
 804	}
 805	if (arch_kgdb_ops.correct_hw_break)
 806		arch_kgdb_ops.correct_hw_break();
 807	if (trace_on)
 808		tracing_on();
 809
 810	kgdb_info[cpu].debuggerinfo = NULL;
 811	kgdb_info[cpu].task = NULL;
 812	kgdb_info[cpu].exception_state &=
 813		~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 814	kgdb_info[cpu].enter_kgdb--;
 815	smp_mb__before_atomic();
 816	atomic_dec(&masters_in_kgdb);
 817	/* Free kgdb_active */
 818	atomic_set(&kgdb_active, -1);
 819	raw_spin_unlock(&dbg_master_lock);
 820	dbg_touch_watchdogs();
 821	local_irq_restore(flags);
 822	rcu_read_unlock();
 823
 824	return kgdb_info[cpu].ret_state;
 825}
 826NOKPROBE_SYMBOL(kgdb_cpu_enter);
 827
 828/*
 829 * kgdb_handle_exception() - main entry point from a kernel exception
 830 *
 831 * Locking hierarchy:
 832 *	interface locks, if any (begin_session)
 833 *	kgdb lock (kgdb_active)
 834 */
 835int
 836kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 837{
 838	struct kgdb_state kgdb_var;
 839	struct kgdb_state *ks = &kgdb_var;
 840	/*
 841	 * Avoid entering the debugger if we were triggered due to an oops
 842	 * but panic_timeout indicates the system should automatically
 843	 * reboot on panic. We don't want to get stuck waiting for input
 844	 * on such systems, especially if its "just" an oops.
 845	 */
 846	if (signo != SIGTRAP && panic_timeout)
 847		return 1;
 848
 849	memset(ks, 0, sizeof(struct kgdb_state));
 850	ks->cpu			= raw_smp_processor_id();
 851	ks->ex_vector		= evector;
 852	ks->signo		= signo;
 853	ks->err_code		= ecode;
 854	ks->linux_regs		= regs;
 855
 856	if (kgdb_reenter_check(ks))
 857		return 0; /* Ouch, double exception ! */
 858	if (kgdb_info[ks->cpu].enter_kgdb != 0)
 859		return 0;
 860
 861	return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 862}
 863NOKPROBE_SYMBOL(kgdb_handle_exception);
 864
 865/*
 866 * GDB places a breakpoint at this function to know dynamically loaded objects.
 867 */
 868static int module_event(struct notifier_block *self, unsigned long val,
 869	void *data)
 870{
 871	return 0;
 872}
 873
 874static struct notifier_block dbg_module_load_nb = {
 875	.notifier_call	= module_event,
 876};
 877
 878int kgdb_nmicallback(int cpu, void *regs)
 879{
 880#ifdef CONFIG_SMP
 881	struct kgdb_state kgdb_var;
 882	struct kgdb_state *ks = &kgdb_var;
 883
 884	kgdb_info[cpu].rounding_up = false;
 885
 886	memset(ks, 0, sizeof(struct kgdb_state));
 887	ks->cpu			= cpu;
 888	ks->linux_regs		= regs;
 889
 890	if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 891			raw_spin_is_locked(&dbg_master_lock)) {
 892		kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 893		return 0;
 894	}
 895#endif
 896	return 1;
 897}
 898NOKPROBE_SYMBOL(kgdb_nmicallback);
 899
 900int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 901							atomic_t *send_ready)
 902{
 903#ifdef CONFIG_SMP
 904	if (!kgdb_io_ready(0) || !send_ready)
 905		return 1;
 906
 907	if (kgdb_info[cpu].enter_kgdb == 0) {
 908		struct kgdb_state kgdb_var;
 909		struct kgdb_state *ks = &kgdb_var;
 910
 911		memset(ks, 0, sizeof(struct kgdb_state));
 912		ks->cpu			= cpu;
 913		ks->ex_vector		= trapnr;
 914		ks->signo		= SIGTRAP;
 915		ks->err_code		= err_code;
 916		ks->linux_regs		= regs;
 917		ks->send_ready		= send_ready;
 918		kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 919		return 0;
 920	}
 921#endif
 922	return 1;
 923}
 924NOKPROBE_SYMBOL(kgdb_nmicallin);
 925
 926static void kgdb_console_write(struct console *co, const char *s,
 927   unsigned count)
 928{
 929	unsigned long flags;
 930
 931	/* If we're debugging, or KGDB has not connected, don't try
 932	 * and print. */
 933	if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 934		return;
 935
 936	local_irq_save(flags);
 937	gdbstub_msg_write(s, count);
 938	local_irq_restore(flags);
 939}
 940
 941static struct console kgdbcons = {
 942	.name		= "kgdb",
 943	.write		= kgdb_console_write,
 944	.flags		= CON_PRINTBUFFER | CON_ENABLED,
 945	.index		= -1,
 946};
 947
 948static int __init opt_kgdb_con(char *str)
 949{
 950	kgdb_use_con = 1;
 951
 952	if (kgdb_io_module_registered && !kgdb_con_registered) {
 953		register_console(&kgdbcons);
 954		kgdb_con_registered = 1;
 955	}
 956
 957	return 0;
 958}
 959
 960early_param("kgdbcon", opt_kgdb_con);
 961
 962#ifdef CONFIG_MAGIC_SYSRQ
 963static void sysrq_handle_dbg(u8 key)
 964{
 965	if (!dbg_io_ops) {
 966		pr_crit("ERROR: No KGDB I/O module available\n");
 967		return;
 968	}
 969	if (!kgdb_connected) {
 970#ifdef CONFIG_KGDB_KDB
 971		if (!dbg_kdb_mode)
 972			pr_crit("KGDB or $3#33 for KDB\n");
 973#else
 974		pr_crit("Entering KGDB\n");
 975#endif
 976	}
 977
 978	kgdb_breakpoint();
 979}
 980
 981static const struct sysrq_key_op sysrq_dbg_op = {
 982	.handler	= sysrq_handle_dbg,
 983	.help_msg	= "debug(g)",
 984	.action_msg	= "DEBUG",
 985};
 986#endif
 987
 988void kgdb_panic(const char *msg)
 989{
 990	if (!kgdb_io_module_registered)
 991		return;
 992
 993	/*
 994	 * We don't want to get stuck waiting for input from user if
 995	 * "panic_timeout" indicates the system should automatically
 996	 * reboot on panic.
 997	 */
 998	if (panic_timeout)
 999		return;
1000
1001	debug_locks_off();
1002	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
1003
1004	if (dbg_kdb_mode)
1005		kdb_printf("PANIC: %s\n", msg);
1006
1007	kgdb_breakpoint();
1008}
1009
1010static void kgdb_initial_breakpoint(void)
1011{
1012	kgdb_break_asap = 0;
1013
1014	pr_crit("Waiting for connection from remote gdb...\n");
1015	kgdb_breakpoint();
1016}
1017
1018void __weak kgdb_arch_late(void)
1019{
1020}
1021
1022void __init dbg_late_init(void)
1023{
1024	dbg_is_early = false;
1025	if (kgdb_io_module_registered)
1026		kgdb_arch_late();
1027	kdb_init(KDB_INIT_FULL);
1028
1029	if (kgdb_io_module_registered && kgdb_break_asap)
1030		kgdb_initial_breakpoint();
1031}
1032
1033static int
1034dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
1035{
1036	/*
1037	 * Take the following action on reboot notify depending on value:
1038	 *    1 == Enter debugger
1039	 *    0 == [the default] detach debug client
1040	 *   -1 == Do nothing... and use this until the board resets
1041	 */
1042	switch (kgdbreboot) {
1043	case 1:
1044		kgdb_breakpoint();
1045		goto done;
1046	case -1:
1047		goto done;
1048	}
1049	if (!dbg_kdb_mode)
1050		gdbstub_exit(code);
1051done:
1052	return NOTIFY_DONE;
1053}
1054
1055static struct notifier_block dbg_reboot_notifier = {
1056	.notifier_call		= dbg_notify_reboot,
1057	.next			= NULL,
1058	.priority		= INT_MAX,
1059};
1060
1061static void kgdb_register_callbacks(void)
1062{
1063	if (!kgdb_io_module_registered) {
1064		kgdb_io_module_registered = 1;
1065		kgdb_arch_init();
1066		if (!dbg_is_early)
1067			kgdb_arch_late();
1068		register_module_notifier(&dbg_module_load_nb);
1069		register_reboot_notifier(&dbg_reboot_notifier);
1070#ifdef CONFIG_MAGIC_SYSRQ
1071		register_sysrq_key('g', &sysrq_dbg_op);
1072#endif
1073		if (kgdb_use_con && !kgdb_con_registered) {
1074			register_console(&kgdbcons);
1075			kgdb_con_registered = 1;
1076		}
1077	}
1078}
1079
1080static void kgdb_unregister_callbacks(void)
1081{
1082	/*
1083	 * When this routine is called KGDB should unregister from
1084	 * handlers and clean up, making sure it is not handling any
1085	 * break exceptions at the time.
1086	 */
1087	if (kgdb_io_module_registered) {
1088		kgdb_io_module_registered = 0;
1089		unregister_reboot_notifier(&dbg_reboot_notifier);
1090		unregister_module_notifier(&dbg_module_load_nb);
1091		kgdb_arch_exit();
1092#ifdef CONFIG_MAGIC_SYSRQ
1093		unregister_sysrq_key('g', &sysrq_dbg_op);
1094#endif
1095		if (kgdb_con_registered) {
1096			unregister_console(&kgdbcons);
1097			kgdb_con_registered = 0;
1098		}
1099	}
1100}
1101
1102/**
1103 *	kgdb_register_io_module - register KGDB IO module
1104 *	@new_dbg_io_ops: the io ops vector
1105 *
1106 *	Register it with the KGDB core.
1107 */
1108int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1109{
1110	struct kgdb_io *old_dbg_io_ops;
1111	int err;
1112
1113	spin_lock(&kgdb_registration_lock);
1114
1115	old_dbg_io_ops = dbg_io_ops;
1116	if (old_dbg_io_ops) {
1117		if (!old_dbg_io_ops->deinit) {
1118			spin_unlock(&kgdb_registration_lock);
1119
1120			pr_err("KGDB I/O driver %s can't replace %s.\n",
1121				new_dbg_io_ops->name, old_dbg_io_ops->name);
1122			return -EBUSY;
1123		}
1124		pr_info("Replacing I/O driver %s with %s\n",
1125			old_dbg_io_ops->name, new_dbg_io_ops->name);
1126	}
1127
1128	if (new_dbg_io_ops->init) {
1129		err = new_dbg_io_ops->init();
1130		if (err) {
1131			spin_unlock(&kgdb_registration_lock);
1132			return err;
1133		}
1134	}
1135
1136	dbg_io_ops = new_dbg_io_ops;
1137
1138	spin_unlock(&kgdb_registration_lock);
1139
1140	if (old_dbg_io_ops) {
1141		old_dbg_io_ops->deinit();
1142		return 0;
1143	}
1144
1145	pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1146
1147	/* Arm KGDB now. */
1148	kgdb_register_callbacks();
1149
1150	if (kgdb_break_asap &&
1151	    (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
1152		kgdb_initial_breakpoint();
1153
1154	return 0;
1155}
1156EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1157
1158/**
1159 *	kgdb_unregister_io_module - unregister KGDB IO module
1160 *	@old_dbg_io_ops: the io ops vector
1161 *
1162 *	Unregister it with the KGDB core.
1163 */
1164void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1165{
1166	BUG_ON(kgdb_connected);
1167
1168	/*
1169	 * KGDB is no longer able to communicate out, so
1170	 * unregister our callbacks and reset state.
1171	 */
1172	kgdb_unregister_callbacks();
1173
1174	spin_lock(&kgdb_registration_lock);
1175
1176	WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1177	dbg_io_ops = NULL;
1178
1179	spin_unlock(&kgdb_registration_lock);
1180
1181	if (old_dbg_io_ops->deinit)
1182		old_dbg_io_ops->deinit();
1183
1184	pr_info("Unregistered I/O driver %s, debugger disabled\n",
1185		old_dbg_io_ops->name);
1186}
1187EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1188
1189int dbg_io_get_char(void)
1190{
1191	int ret = dbg_io_ops->read_char();
1192	if (ret == NO_POLL_CHAR)
1193		return -1;
1194	if (!dbg_kdb_mode)
1195		return ret;
1196	if (ret == 127)
1197		return 8;
1198	return ret;
1199}
1200
1201/**
1202 * kgdb_breakpoint - generate breakpoint exception
1203 *
1204 * This function will generate a breakpoint exception.  It is used at the
1205 * beginning of a program to sync up with a debugger and can be used
1206 * otherwise as a quick means to stop program execution and "break" into
1207 * the debugger.
1208 */
1209noinline void kgdb_breakpoint(void)
1210{
1211	atomic_inc(&kgdb_setting_breakpoint);
1212	wmb(); /* Sync point before breakpoint */
1213	arch_kgdb_breakpoint();
1214	wmb(); /* Sync point after breakpoint */
1215	atomic_dec(&kgdb_setting_breakpoint);
1216}
1217EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1218
1219static int __init opt_kgdb_wait(char *str)
1220{
1221	kgdb_break_asap = 1;
1222
1223	kdb_init(KDB_INIT_EARLY);
1224	if (kgdb_io_module_registered &&
1225	    IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
1226		kgdb_initial_breakpoint();
1227
1228	return 0;
1229}
1230
1231early_param("kgdbwait", opt_kgdb_wait);