kernel/debug/debug_core.c

   1 /*
   2  * Kernel Debug Core
   3  *
   4  * Maintainer: Jason Wessel <jason.wessel@windriver.com>
   5  *
   6  * Copyright (C) 2000-2001 VERITAS Software Corporation.
   7  * Copyright (C) 2002-2004 Timesys Corporation
   8  * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
   9  * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
  10  * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
  11  * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
  12  * Copyright (C) 2005-2009 Wind River Systems, Inc.
  13  * Copyright (C) 2007 MontaVista Software, Inc.
  14  * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  15  *
  16  * Contributors at various stages not listed above:
  17  *  Jason Wessel ( jason.wessel@windriver.com )
  18  *  George Anzinger <george@mvista.com>
  19  *  Anurekh Saxena (anurekh.saxena@timesys.com)
  20  *  Lake Stevens Instrument Division (Glenn Engel)
  21  *  Jim Kingdon, Cygnus Support.
  22  *
  23  * Original KGDB stub: David Grothe <dave@gcom.com>,
  24  * Tigran Aivazian <tigran@sco.com>
  25  *
  26  * This file is licensed under the terms of the GNU General Public License
  27  * version 2. This program is licensed "as is" without any warranty of any
  28  * kind, whether express or implied.
  29  */
  30
  31 #define pr_fmt(fmt) "KGDB: " fmt
  32
  33 #include <linux/pid_namespace.h>
  34 #include <linux/clocksource.h>
  35 #include <linux/serial_core.h>
  36 #include <linux/interrupt.h>
  37 #include <linux/spinlock.h>
  38 #include <linux/console.h>
  39 #include <linux/threads.h>
  40 #include <linux/uaccess.h>
  41 #include <linux/kernel.h>
  42 #include <linux/module.h>
  43 #include <linux/ptrace.h>
  44 #include <linux/string.h>
  45 #include <linux/delay.h>
  46 #include <linux/sched.h>
  47 #include <linux/sysrq.h>
  48 #include <linux/reboot.h>
  49 #include <linux/init.h>
  50 #include <linux/kgdb.h>
  51 #include <linux/kdb.h>
  52 #include <linux/nmi.h>
  53 #include <linux/pid.h>
  54 #include <linux/smp.h>
  55 #include <linux/mm.h>
  56 #include <linux/vmacache.h>
  57 #include <linux/rcupdate.h>
  58 #include <linux/irq.h>
  59 #include <linux/security.h>
  60
  61 #include <asm/cacheflush.h>
  62 #include <asm/byteorder.h>
  63 #include <linux/atomic.h>
  64
  65 #include "debug_core.h"
  66
  67 static int kgdb_break_asap;
  68
  69 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  70
  71 /* kgdb_connected - Is a host GDB connected to us? */
  72 int                             kgdb_connected;
  73 EXPORT_SYMBOL_GPL(kgdb_connected);
  74
  75 /* All the KGDB handlers are installed */
  76 int                     kgdb_io_module_registered;
  77
  78 /* Guard for recursive entry */
  79 static int                      exception_level;
  80
  81 struct kgdb_io          *dbg_io_ops;
  82 static DEFINE_SPINLOCK(kgdb_registration_lock);
  83
  84 /* Action for the reboot notifier, a global allow kdb to change it */
  85 static int kgdbreboot;
  86 /* kgdb console driver is loaded */
  87 static int kgdb_con_registered;
  88 /* determine if kgdb console output should be used */
  89 static int kgdb_use_con;
  90 /* Flag for alternate operations for early debugging */
  91 bool dbg_is_early = true;
  92 /* Next cpu to become the master debug core */
  93 int dbg_switch_cpu;
  94
  95 /* Use kdb or gdbserver mode */
  96 int dbg_kdb_mode = 1;
  97
  98 module_param(kgdb_use_con, int, 0644);
  99 module_param(kgdbreboot, int, 0644);
 100
 101 /*
 102  * Holds information about breakpoints in a kernel. These breakpoints are
 103  * added and removed by gdb.
 104  */
 105 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 106         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 107 };
 108
 109 /*
 110  * The CPU# of the active CPU, or -1 if none:
 111  */
 112 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 113 EXPORT_SYMBOL_GPL(kgdb_active);
 114 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 115 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 116
 117 /*
 118  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 119  * bootup code (which might not have percpu set up yet):
 120  */
 121 static atomic_t                 masters_in_kgdb;
 122 static atomic_t                 slaves_in_kgdb;
 123 static atomic_t                 kgdb_break_tasklet_var;
 124 atomic_t                        kgdb_setting_breakpoint;
 125
 126 struct task_struct              *kgdb_usethread;
 127 struct task_struct              *kgdb_contthread;
 128
 129 int                             kgdb_single_step;
 130 static pid_t                    kgdb_sstep_pid;
 131
 132 /* to keep track of the CPU which is doing the single stepping*/
 133 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 134
 135 /*
 136  * If you are debugging a problem where roundup (the collection of
 137  * all other CPUs) is a problem [this should be extremely rare],
 138  * then use the nokgdbroundup option to avoid roundup. In that case
 139  * the other CPUs might interfere with your debugging context, so
 140  * use this with care:
 141  */
 142 static int kgdb_do_roundup = 1;
 143
 144 static int __init opt_nokgdbroundup(char *str)
 145 {
 146         kgdb_do_roundup = 0;
 147
 148         return 0;
 149 }
 150
 151 early_param("nokgdbroundup", opt_nokgdbroundup);
 152
 153 /*
 154  * Finally, some KGDB code :-)
 155  */
 156
 157 /*
 158  * Weak aliases for breakpoint management,
 159  * can be overridden by architectures when needed:
 160  */
 161 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 162 {
 163         int err;
 164
 165         err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
 166                                 BREAK_INSTR_SIZE);
 167         if (err)
 168                 return err;
 169         err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
 170                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 171         return err;
 172 }
 173 NOKPROBE_SYMBOL(kgdb_arch_set_breakpoint);
 174
 175 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 176 {
 177         return copy_to_kernel_nofault((char *)bpt->bpt_addr,
 178                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 179 }
 180 NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
 181
 182 int __weak kgdb_validate_break_address(unsigned long addr)
 183 {
 184         struct kgdb_bkpt tmp;
 185         int err;
 186
 187         if (kgdb_within_blocklist(addr))
 188                 return -EINVAL;
 189
 190         /* Validate setting the breakpoint and then removing it.  If the
 191          * remove fails, the kernel needs to emit a bad message because we
 192          * are deep trouble not being able to put things back the way we
 193          * found them.
 194          */
 195         tmp.bpt_addr = addr;
 196         err = kgdb_arch_set_breakpoint(&tmp);
 197         if (err)
 198                 return err;
 199         err = kgdb_arch_remove_breakpoint(&tmp);
 200         if (err)
 201                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
 202                        addr);
 203         return err;
 204 }
 205
 206 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 207 {
 208         return instruction_pointer(regs);
 209 }
 210 NOKPROBE_SYMBOL(kgdb_arch_pc);
 211
 212 int __weak kgdb_arch_init(void)
 213 {
 214         return 0;
 215 }
 216
 217 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 218 {
 219         return 0;
 220 }
 221 NOKPROBE_SYMBOL(kgdb_skipexception);
 222
 223 #ifdef CONFIG_SMP
 224
 225 /*
 226  * Default (weak) implementation for kgdb_roundup_cpus
 227  */
 228
 229 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd);
 230
 231 void __weak kgdb_call_nmi_hook(void *ignored)
 232 {
 233         /*
 234          * NOTE: get_irq_regs() is supposed to get the registers from
 235          * before the IPI interrupt happened and so is supposed to
 236          * show where the processor was.  In some situations it's
 237          * possible we might be called without an IPI, so it might be
 238          * safer to figure out how to make kgdb_breakpoint() work
 239          * properly here.
 240          */
 241         kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 242 }
 243 NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 244
 245 void __weak kgdb_roundup_cpus(void)
 246 {
 247         call_single_data_t *csd;
 248         int this_cpu = raw_smp_processor_id();
 249         int cpu;
 250         int ret;
 251
 252         for_each_online_cpu(cpu) {
 253                 /* No need to roundup ourselves */
 254                 if (cpu == this_cpu)
 255                         continue;
 256
 257                 csd = &per_cpu(kgdb_roundup_csd, cpu);
 258
 259                 /*
 260                  * If it didn't round up last time, don't try again
 261                  * since smp_call_function_single_async() will block.
 262                  *
 263                  * If rounding_up is false then we know that the
 264                  * previous call must have at least started and that
 265                  * means smp_call_function_single_async() won't block.
 266                  */
 267                 if (kgdb_info[cpu].rounding_up)
 268                         continue;
 269                 kgdb_info[cpu].rounding_up = true;
 270
 271                 csd->func = kgdb_call_nmi_hook;
 272                 ret = smp_call_function_single_async(cpu, csd);
 273                 if (ret)
 274                         kgdb_info[cpu].rounding_up = false;
 275         }
 276 }
 277 NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 278
 279 #endif
 280
 281 /*
 282  * Some architectures need cache flushes when we set/clear a
 283  * breakpoint:
 284  */
 285 static void kgdb_flush_swbreak_addr(unsigned long addr)
 286 {
 287         if (!CACHE_FLUSH_IS_SAFE)
 288                 return;
 289
 290         if (current->mm) {
 291                 int i;
 292
 293                 for (i = 0; i < VMACACHE_SIZE; i++) {
 294                         if (!current->vmacache.vmas[i])
 295                                 continue;
 296                         flush_cache_range(current->vmacache.vmas[i],
 297                                           addr, addr + BREAK_INSTR_SIZE);
 298                 }
 299         }
 300
 301         /* Force flush instruction cache if it was outside the mm */
 302         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 303 }
 304 NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
 305
 306 /*
 307  * SW breakpoint management:
 308  */
 309 int dbg_activate_sw_breakpoints(void)
 310 {
 311         int error;
 312         int ret = 0;
 313         int i;
 314
 315         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 316                 if (kgdb_break[i].state != BP_SET)
 317                         continue;
 318
 319                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 320                 if (error) {
 321                         ret = error;
 322                         pr_info("BP install failed: %lx\n",
 323                                 kgdb_break[i].bpt_addr);
 324                         continue;
 325                 }
 326
 327                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 328                 kgdb_break[i].state = BP_ACTIVE;
 329         }
 330         return ret;
 331 }
 332 NOKPROBE_SYMBOL(dbg_activate_sw_breakpoints);
 333
 334 int dbg_set_sw_break(unsigned long addr)
 335 {
 336         int err = kgdb_validate_break_address(addr);
 337         int breakno = -1;
 338         int i;
 339
 340         if (err)
 341                 return err;
 342
 343         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 344                 if ((kgdb_break[i].state == BP_SET) &&
 345                                         (kgdb_break[i].bpt_addr == addr))
 346                         return -EEXIST;
 347         }
 348         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 349                 if (kgdb_break[i].state == BP_REMOVED &&
 350                                         kgdb_break[i].bpt_addr == addr) {
 351                         breakno = i;
 352                         break;
 353                 }
 354         }
 355
 356         if (breakno == -1) {
 357                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 358                         if (kgdb_break[i].state == BP_UNDEFINED) {
 359                                 breakno = i;
 360                                 break;
 361                         }
 362                 }
 363         }
 364
 365         if (breakno == -1)
 366                 return -E2BIG;
 367
 368         kgdb_break[breakno].state = BP_SET;
 369         kgdb_break[breakno].type = BP_BREAKPOINT;
 370         kgdb_break[breakno].bpt_addr = addr;
 371
 372         return 0;
 373 }
 374
 375 int dbg_deactivate_sw_breakpoints(void)
 376 {
 377         int error;
 378         int ret = 0;
 379         int i;
 380
 381         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 382                 if (kgdb_break[i].state != BP_ACTIVE)
 383                         continue;
 384                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 385                 if (error) {
 386                         pr_info("BP remove failed: %lx\n",
 387                                 kgdb_break[i].bpt_addr);
 388                         ret = error;
 389                 }
 390
 391                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 392                 kgdb_break[i].state = BP_SET;
 393         }
 394         return ret;
 395 }
 396 NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
 397
 398 int dbg_remove_sw_break(unsigned long addr)
 399 {
 400         int i;
 401
 402         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 403                 if ((kgdb_break[i].state == BP_SET) &&
 404                                 (kgdb_break[i].bpt_addr == addr)) {
 405                         kgdb_break[i].state = BP_REMOVED;
 406                         return 0;
 407                 }
 408         }
 409         return -ENOENT;
 410 }
 411
 412 int kgdb_isremovedbreak(unsigned long addr)
 413 {
 414         int i;
 415
 416         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 417                 if ((kgdb_break[i].state == BP_REMOVED) &&
 418                                         (kgdb_break[i].bpt_addr == addr))
 419                         return 1;
 420         }
 421         return 0;
 422 }
 423
 424 int kgdb_has_hit_break(unsigned long addr)
 425 {
 426         int i;
 427
 428         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 429                 if (kgdb_break[i].state == BP_ACTIVE &&
 430                     kgdb_break[i].bpt_addr == addr)
 431                         return 1;
 432         }
 433         return 0;
 434 }
 435
 436 int dbg_remove_all_break(void)
 437 {
 438         int error;
 439         int i;
 440
 441         /* Clear memory breakpoints. */
 442         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 443                 if (kgdb_break[i].state != BP_ACTIVE)
 444                         goto setundefined;
 445                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 446                 if (error)
 447                         pr_err("breakpoint remove failed: %lx\n",
 448                                kgdb_break[i].bpt_addr);
 449 setundefined:
 450                 kgdb_break[i].state = BP_UNDEFINED;
 451         }
 452
 453         /* Clear hardware breakpoints. */
 454         if (arch_kgdb_ops.remove_all_hw_break)
 455                 arch_kgdb_ops.remove_all_hw_break();
 456
 457         return 0;
 458 }
 459
 460 void kgdb_free_init_mem(void)
 461 {
 462         int i;
 463
 464         /* Clear init memory breakpoints. */
 465         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 466                 if (init_section_contains((void *)kgdb_break[i].bpt_addr, 0))
 467                         kgdb_break[i].state = BP_UNDEFINED;
 468         }
 469 }
 470
 471 #ifdef CONFIG_KGDB_KDB
 472 void kdb_dump_stack_on_cpu(int cpu)
 473 {
 474         if (cpu == raw_smp_processor_id() || !IS_ENABLED(CONFIG_SMP)) {
 475                 dump_stack();
 476                 return;
 477         }
 478
 479         if (!(kgdb_info[cpu].exception_state & DCPU_IS_SLAVE)) {
 480                 kdb_printf("ERROR: Task on cpu %d didn't stop in the debugger\n",
 481                            cpu);
 482                 return;
 483         }
 484
 485         /*
 486          * In general, architectures don't support dumping the stack of a
 487          * "running" process that's not the current one.  From the point of
 488          * view of the Linux, kernel processes that are looping in the kgdb
 489          * slave loop are still "running".  There's also no API (that actually
 490          * works across all architectures) that can do a stack crawl based
 491          * on registers passed as a parameter.
 492          *
 493          * Solve this conundrum by asking slave CPUs to do the backtrace
 494          * themselves.
 495          */
 496         kgdb_info[cpu].exception_state |= DCPU_WANT_BT;
 497         while (kgdb_info[cpu].exception_state & DCPU_WANT_BT)
 498                 cpu_relax();
 499 }
 500 #endif
 501
 502 /*
 503  * Return true if there is a valid kgdb I/O module.  Also if no
 504  * debugger is attached a message can be printed to the console about
 505  * waiting for the debugger to attach.
 506  *
 507  * The print_wait argument is only to be true when called from inside
 508  * the core kgdb_handle_exception, because it will wait for the
 509  * debugger to attach.
 510  */
 511 static int kgdb_io_ready(int print_wait)
 512 {
 513         if (!dbg_io_ops)
 514                 return 0;
 515         if (kgdb_connected)
 516                 return 1;
 517         if (atomic_read(&kgdb_setting_breakpoint))
 518                 return 1;
 519         if (print_wait) {
 520 #ifdef CONFIG_KGDB_KDB
 521                 if (!dbg_kdb_mode)
 522                         pr_crit("waiting... or $3#33 for KDB\n");
 523 #else
 524                 pr_crit("Waiting for remote debugger\n");
 525 #endif
 526         }
 527         return 1;
 528 }
 529 NOKPROBE_SYMBOL(kgdb_io_ready);
 530
 531 static int kgdb_reenter_check(struct kgdb_state *ks)
 532 {
 533         unsigned long addr;
 534
 535         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 536                 return 0;
 537
 538         /* Panic on recursive debugger calls: */
 539         exception_level++;
 540         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 541         dbg_deactivate_sw_breakpoints();
 542
 543         /*
 544          * If the break point removed ok at the place exception
 545          * occurred, try to recover and print a warning to the end
 546          * user because the user planted a breakpoint in a place that
 547          * KGDB needs in order to function.
 548          */
 549         if (dbg_remove_sw_break(addr) == 0) {
 550                 exception_level = 0;
 551                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 552                 dbg_activate_sw_breakpoints();
 553                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 554                 WARN_ON_ONCE(1);
 555
 556                 return 1;
 557         }
 558         dbg_remove_all_break();
 559         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 560
 561         if (exception_level > 1) {
 562                 dump_stack();
 563                 kgdb_io_module_registered = false;
 564                 panic("Recursive entry to debugger");
 565         }
 566
 567         pr_crit("re-enter exception: ALL breakpoints killed\n");
 568 #ifdef CONFIG_KGDB_KDB
 569         /* Allow kdb to debug itself one level */
 570         return 0;
 571 #endif
 572         dump_stack();
 573         panic("Recursive entry to debugger");
 574
 575         return 1;
 576 }
 577 NOKPROBE_SYMBOL(kgdb_reenter_check);
 578
 579 static void dbg_touch_watchdogs(void)
 580 {
 581         touch_softlockup_watchdog_sync();
 582         clocksource_touch_watchdog();
 583         rcu_cpu_stall_reset();
 584 }
 585 NOKPROBE_SYMBOL(dbg_touch_watchdogs);
 586
 587 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 588                 int exception_state)
 589 {
 590         unsigned long flags;
 591         int sstep_tries = 100;
 592         int error;
 593         int cpu;
 594         int trace_on = 0;
 595         int online_cpus = num_online_cpus();
 596         u64 time_left;
 597
 598         kgdb_info[ks->cpu].enter_kgdb++;
 599         kgdb_info[ks->cpu].exception_state |= exception_state;
 600
 601         if (exception_state == DCPU_WANT_MASTER)
 602                 atomic_inc(&masters_in_kgdb);
 603         else
 604                 atomic_inc(&slaves_in_kgdb);
 605
 606         if (arch_kgdb_ops.disable_hw_break)
 607                 arch_kgdb_ops.disable_hw_break(regs);
 608
 609 acquirelock:
 610         rcu_read_lock();
 611         /*
 612          * Interrupts will be restored by the 'trap return' code, except when
 613          * single stepping.
 614          */
 615         local_irq_save(flags);
 616
 617         cpu = ks->cpu;
 618         kgdb_info[cpu].debuggerinfo = regs;
 619         kgdb_info[cpu].task = current;
 620         kgdb_info[cpu].ret_state = 0;
 621         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 622
 623         /* Make sure the above info reaches the primary CPU */
 624         smp_mb();
 625
 626         if (exception_level == 1) {
 627                 if (raw_spin_trylock(&dbg_master_lock))
 628                         atomic_xchg(&kgdb_active, cpu);
 629                 goto cpu_master_loop;
 630         }
 631
 632         /*
 633          * CPU will loop if it is a slave or request to become a kgdb
 634          * master cpu and acquire the kgdb_active lock:
 635          */
 636         while (1) {
 637 cpu_loop:
 638                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 639                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 640                         goto cpu_master_loop;
 641                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 642                         if (raw_spin_trylock(&dbg_master_lock)) {
 643                                 atomic_xchg(&kgdb_active, cpu);
 644                                 break;
 645                         }
 646                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_BT) {
 647                         dump_stack();
 648                         kgdb_info[cpu].exception_state &= ~DCPU_WANT_BT;
 649                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 650                         if (!raw_spin_is_locked(&dbg_slave_lock))
 651                                 goto return_normal;
 652                 } else {
 653 return_normal:
 654                         /* Return to normal operation by executing any
 655                          * hw breakpoint fixup.
 656                          */
 657                         if (arch_kgdb_ops.correct_hw_break)
 658                                 arch_kgdb_ops.correct_hw_break();
 659                         if (trace_on)
 660                                 tracing_on();
 661                         kgdb_info[cpu].debuggerinfo = NULL;
 662                         kgdb_info[cpu].task = NULL;
 663                         kgdb_info[cpu].exception_state &=
 664                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 665                         kgdb_info[cpu].enter_kgdb--;
 666                         smp_mb__before_atomic();
 667                         atomic_dec(&slaves_in_kgdb);
 668                         dbg_touch_watchdogs();
 669                         local_irq_restore(flags);
 670                         rcu_read_unlock();
 671                         return 0;
 672                 }
 673                 cpu_relax();
 674         }
 675
 676         /*
 677          * For single stepping, try to only enter on the processor
 678          * that was single stepping.  To guard against a deadlock, the
 679          * kernel will only try for the value of sstep_tries before
 680          * giving up and continuing on.
 681          */
 682         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 683             (kgdb_info[cpu].task &&
 684              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 685                 atomic_set(&kgdb_active, -1);
 686                 raw_spin_unlock(&dbg_master_lock);
 687                 dbg_touch_watchdogs();
 688                 local_irq_restore(flags);
 689                 rcu_read_unlock();
 690
 691                 goto acquirelock;
 692         }
 693
 694         if (!kgdb_io_ready(1)) {
 695                 kgdb_info[cpu].ret_state = 1;
 696                 goto kgdb_restore; /* No I/O connection, resume the system */
 697         }
 698
 699         /*
 700          * Don't enter if we have hit a removed breakpoint.
 701          */
 702         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 703                 goto kgdb_restore;
 704
 705         atomic_inc(&ignore_console_lock_warning);
 706
 707         /* Call the I/O driver's pre_exception routine */
 708         if (dbg_io_ops->pre_exception)
 709                 dbg_io_ops->pre_exception();
 710
 711         /*
 712          * Get the passive CPU lock which will hold all the non-primary
 713          * CPU in a spin state while the debugger is active
 714          */
 715         if (!kgdb_single_step)
 716                 raw_spin_lock(&dbg_slave_lock);
 717
 718 #ifdef CONFIG_SMP
 719         /* If send_ready set, slaves are already waiting */
 720         if (ks->send_ready)
 721                 atomic_set(ks->send_ready, 1);
 722
 723         /* Signal the other CPUs to enter kgdb_wait() */
 724         else if ((!kgdb_single_step) && kgdb_do_roundup)
 725                 kgdb_roundup_cpus();
 726 #endif
 727
 728         /*
 729          * Wait for the other CPUs to be notified and be waiting for us:
 730          */
 731         time_left = MSEC_PER_SEC;
 732         while (kgdb_do_roundup && --time_left &&
 733                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
 734                    online_cpus)
 735                 udelay(1000);
 736         if (!time_left)
 737                 pr_crit("Timed out waiting for secondary CPUs.\n");
 738
 739         /*
 740          * At this point the primary processor is completely
 741          * in the debugger and all secondary CPUs are quiescent
 742          */
 743         dbg_deactivate_sw_breakpoints();
 744         kgdb_single_step = 0;
 745         kgdb_contthread = current;
 746         exception_level = 0;
 747         trace_on = tracing_is_on();
 748         if (trace_on)
 749                 tracing_off();
 750
 751         while (1) {
 752 cpu_master_loop:
 753                 if (dbg_kdb_mode) {
 754                         kgdb_connected = 1;
 755                         error = kdb_stub(ks);
 756                         if (error == -1)
 757                                 continue;
 758                         kgdb_connected = 0;
 759                 } else {
 760                         /*
 761                          * This is a brutal way to interfere with the debugger
 762                          * and prevent gdb being used to poke at kernel memory.
 763                          * This could cause trouble if lockdown is applied when
 764                          * there is already an active gdb session. For now the
 765                          * answer is simply "don't do that". Typically lockdown
 766                          * *will* be applied before the debug core gets started
 767                          * so only developers using kgdb for fairly advanced
 768                          * early kernel debug can be biten by this. Hopefully
 769                          * they are sophisticated enough to take care of
 770                          * themselves, especially with help from the lockdown
 771                          * message printed on the console!
 772                          */
 773                         if (security_locked_down(LOCKDOWN_DBG_WRITE_KERNEL)) {
 774                                 if (IS_ENABLED(CONFIG_KGDB_KDB)) {
 775                                         /* Switch back to kdb if possible... */
 776                                         dbg_kdb_mode = 1;
 777                                         continue;
 778                                 } else {
 779                                         /* ... otherwise just bail */
 780                                         break;
 781                                 }
 782                         }
 783                         error = gdb_serial_stub(ks);
 784                 }
 785
 786                 if (error == DBG_PASS_EVENT) {
 787                         dbg_kdb_mode = !dbg_kdb_mode;
 788                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 789                         kgdb_info[dbg_switch_cpu].exception_state |=
 790                                 DCPU_NEXT_MASTER;
 791                         goto cpu_loop;
 792                 } else {
 793                         kgdb_info[cpu].ret_state = error;
 794                         break;
 795                 }
 796         }
 797
 798         dbg_activate_sw_breakpoints();
 799
 800         /* Call the I/O driver's post_exception routine */
 801         if (dbg_io_ops->post_exception)
 802                 dbg_io_ops->post_exception();
 803
 804         atomic_dec(&ignore_console_lock_warning);
 805
 806         if (!kgdb_single_step) {
 807                 raw_spin_unlock(&dbg_slave_lock);
 808                 /* Wait till all the CPUs have quit from the debugger. */
 809                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 810                         cpu_relax();
 811         }
 812
 813 kgdb_restore:
 814         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 815                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 816                 if (kgdb_info[sstep_cpu].task)
 817                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 818                 else
 819                         kgdb_sstep_pid = 0;
 820         }
 821         if (arch_kgdb_ops.correct_hw_break)
 822                 arch_kgdb_ops.correct_hw_break();
 823         if (trace_on)
 824                 tracing_on();
 825
 826         kgdb_info[cpu].debuggerinfo = NULL;
 827         kgdb_info[cpu].task = NULL;
 828         kgdb_info[cpu].exception_state &=
 829                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 830         kgdb_info[cpu].enter_kgdb--;
 831         smp_mb__before_atomic();
 832         atomic_dec(&masters_in_kgdb);
 833         /* Free kgdb_active */
 834         atomic_set(&kgdb_active, -1);
 835         raw_spin_unlock(&dbg_master_lock);
 836         dbg_touch_watchdogs();
 837         local_irq_restore(flags);
 838         rcu_read_unlock();
 839
 840         return kgdb_info[cpu].ret_state;
 841 }
 842 NOKPROBE_SYMBOL(kgdb_cpu_enter);
 843
 844 /*
 845  * kgdb_handle_exception() - main entry point from a kernel exception
 846  *
 847  * Locking hierarchy:
 848  *      interface locks, if any (begin_session)
 849  *      kgdb lock (kgdb_active)
 850  */
 851 int
 852 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 853 {
 854         struct kgdb_state kgdb_var;
 855         struct kgdb_state *ks = &kgdb_var;
 856         int ret = 0;
 857
 858         if (arch_kgdb_ops.enable_nmi)
 859                 arch_kgdb_ops.enable_nmi(0);
 860         /*
 861          * Avoid entering the debugger if we were triggered due to an oops
 862          * but panic_timeout indicates the system should automatically
 863          * reboot on panic. We don't want to get stuck waiting for input
 864          * on such systems, especially if its "just" an oops.
 865          */
 866         if (signo != SIGTRAP && panic_timeout)
 867                 return 1;
 868
 869         memset(ks, 0, sizeof(struct kgdb_state));
 870         ks->cpu                 = raw_smp_processor_id();
 871         ks->ex_vector           = evector;
 872         ks->signo               = signo;
 873         ks->err_code            = ecode;
 874         ks->linux_regs          = regs;
 875
 876         if (kgdb_reenter_check(ks))
 877                 goto out; /* Ouch, double exception ! */
 878         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 879                 goto out;
 880
 881         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 882 out:
 883         if (arch_kgdb_ops.enable_nmi)
 884                 arch_kgdb_ops.enable_nmi(1);
 885         return ret;
 886 }
 887 NOKPROBE_SYMBOL(kgdb_handle_exception);
 888
 889 /*
 890  * GDB places a breakpoint at this function to know dynamically loaded objects.
 891  */
 892 static int module_event(struct notifier_block *self, unsigned long val,
 893         void *data)
 894 {
 895         return 0;
 896 }
 897
 898 static struct notifier_block dbg_module_load_nb = {
 899         .notifier_call  = module_event,
 900 };
 901
 902 int kgdb_nmicallback(int cpu, void *regs)
 903 {
 904 #ifdef CONFIG_SMP
 905         struct kgdb_state kgdb_var;
 906         struct kgdb_state *ks = &kgdb_var;
 907
 908         kgdb_info[cpu].rounding_up = false;
 909
 910         memset(ks, 0, sizeof(struct kgdb_state));
 911         ks->cpu                 = cpu;
 912         ks->linux_regs          = regs;
 913
 914         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 915                         raw_spin_is_locked(&dbg_master_lock)) {
 916                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 917                 return 0;
 918         }
 919 #endif
 920         return 1;
 921 }
 922 NOKPROBE_SYMBOL(kgdb_nmicallback);
 923
 924 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 925                                                         atomic_t *send_ready)
 926 {
 927 #ifdef CONFIG_SMP
 928         if (!kgdb_io_ready(0) || !send_ready)
 929                 return 1;
 930
 931         if (kgdb_info[cpu].enter_kgdb == 0) {
 932                 struct kgdb_state kgdb_var;
 933                 struct kgdb_state *ks = &kgdb_var;
 934
 935                 memset(ks, 0, sizeof(struct kgdb_state));
 936                 ks->cpu                 = cpu;
 937                 ks->ex_vector           = trapnr;
 938                 ks->signo               = SIGTRAP;
 939                 ks->err_code            = err_code;
 940                 ks->linux_regs          = regs;
 941                 ks->send_ready          = send_ready;
 942                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 943                 return 0;
 944         }
 945 #endif
 946         return 1;
 947 }
 948 NOKPROBE_SYMBOL(kgdb_nmicallin);
 949
 950 static void kgdb_console_write(struct console *co, const char *s,
 951    unsigned count)
 952 {
 953         unsigned long flags;
 954
 955         /* If we're debugging, or KGDB has not connected, don't try
 956          * and print. */
 957         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 958                 return;
 959
 960         local_irq_save(flags);
 961         gdbstub_msg_write(s, count);
 962         local_irq_restore(flags);
 963 }
 964
 965 static struct console kgdbcons = {
 966         .name           = "kgdb",
 967         .write          = kgdb_console_write,
 968         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 969         .index          = -1,
 970 };
 971
 972 static int __init opt_kgdb_con(char *str)
 973 {
 974         kgdb_use_con = 1;
 975
 976         if (kgdb_io_module_registered && !kgdb_con_registered) {
 977                 register_console(&kgdbcons);
 978                 kgdb_con_registered = 1;
 979         }
 980
 981         return 0;
 982 }
 983
 984 early_param("kgdbcon", opt_kgdb_con);
 985
 986 #ifdef CONFIG_MAGIC_SYSRQ
 987 static void sysrq_handle_dbg(int key)
 988 {
 989         if (!dbg_io_ops) {
 990                 pr_crit("ERROR: No KGDB I/O module available\n");
 991                 return;
 992         }
 993         if (!kgdb_connected) {
 994 #ifdef CONFIG_KGDB_KDB
 995                 if (!dbg_kdb_mode)
 996                         pr_crit("KGDB or $3#33 for KDB\n");
 997 #else
 998                 pr_crit("Entering KGDB\n");
 999 #endif
1000         }
1001
1002         kgdb_breakpoint();
1003 }
1004
1005 static const struct sysrq_key_op sysrq_dbg_op = {
1006         .handler        = sysrq_handle_dbg,
1007         .help_msg       = "debug(g)",
1008         .action_msg     = "DEBUG",
1009 };
1010 #endif
1011
1012 void kgdb_panic(const char *msg)
1013 {
1014         if (!kgdb_io_module_registered)
1015                 return;
1016
1017         /*
1018          * We don't want to get stuck waiting for input from user if
1019          * "panic_timeout" indicates the system should automatically
1020          * reboot on panic.
1021          */
1022         if (panic_timeout)
1023                 return;
1024
1025         debug_locks_off();
1026         console_flush_on_panic(CONSOLE_FLUSH_PENDING);
1027
1028         if (dbg_kdb_mode)
1029                 kdb_printf("PANIC: %s\n", msg);
1030
1031         kgdb_breakpoint();
1032 }
1033
1034 static void kgdb_initial_breakpoint(void)
1035 {
1036         kgdb_break_asap = 0;
1037
1038         pr_crit("Waiting for connection from remote gdb...\n");
1039         kgdb_breakpoint();
1040 }
1041
1042 void __weak kgdb_arch_late(void)
1043 {
1044 }
1045
1046 void __init dbg_late_init(void)
1047 {
1048         dbg_is_early = false;
1049         if (kgdb_io_module_registered)
1050                 kgdb_arch_late();
1051         kdb_init(KDB_INIT_FULL);
1052
1053         if (kgdb_io_module_registered && kgdb_break_asap)
1054                 kgdb_initial_breakpoint();
1055 }
1056
1057 static int
1058 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
1059 {
1060         /*
1061          * Take the following action on reboot notify depending on value:
1062          *    1 == Enter debugger
1063          *    0 == [the default] detatch debug client
1064          *   -1 == Do nothing... and use this until the board resets
1065          */
1066         switch (kgdbreboot) {
1067         case 1:
1068                 kgdb_breakpoint();
1069         case -1:
1070                 goto done;
1071         }
1072         if (!dbg_kdb_mode)
1073                 gdbstub_exit(code);
1074 done:
1075         return NOTIFY_DONE;
1076 }
1077
1078 static struct notifier_block dbg_reboot_notifier = {
1079         .notifier_call          = dbg_notify_reboot,
1080         .next                   = NULL,
1081         .priority               = INT_MAX,
1082 };
1083
1084 static void kgdb_register_callbacks(void)
1085 {
1086         if (!kgdb_io_module_registered) {
1087                 kgdb_io_module_registered = 1;
1088                 kgdb_arch_init();
1089                 if (!dbg_is_early)
1090                         kgdb_arch_late();
1091                 register_module_notifier(&dbg_module_load_nb);
1092                 register_reboot_notifier(&dbg_reboot_notifier);
1093 #ifdef CONFIG_MAGIC_SYSRQ
1094                 register_sysrq_key('g', &sysrq_dbg_op);
1095 #endif
1096                 if (kgdb_use_con && !kgdb_con_registered) {
1097                         register_console(&kgdbcons);
1098                         kgdb_con_registered = 1;
1099                 }
1100         }
1101 }
1102
1103 static void kgdb_unregister_callbacks(void)
1104 {
1105         /*
1106          * When this routine is called KGDB should unregister from
1107          * handlers and clean up, making sure it is not handling any
1108          * break exceptions at the time.
1109          */
1110         if (kgdb_io_module_registered) {
1111                 kgdb_io_module_registered = 0;
1112                 unregister_reboot_notifier(&dbg_reboot_notifier);
1113                 unregister_module_notifier(&dbg_module_load_nb);
1114                 kgdb_arch_exit();
1115 #ifdef CONFIG_MAGIC_SYSRQ
1116                 unregister_sysrq_key('g', &sysrq_dbg_op);
1117 #endif
1118                 if (kgdb_con_registered) {
1119                         unregister_console(&kgdbcons);
1120                         kgdb_con_registered = 0;
1121                 }
1122         }
1123 }
1124
1125 /*
1126  * There are times a tasklet needs to be used vs a compiled in
1127  * break point so as to cause an exception outside a kgdb I/O module,
1128  * such as is the case with kgdboe, where calling a breakpoint in the
1129  * I/O driver itself would be fatal.
1130  */
1131 static void kgdb_tasklet_bpt(unsigned long ing)
1132 {
1133         kgdb_breakpoint();
1134         atomic_set(&kgdb_break_tasklet_var, 0);
1135 }
1136
1137 static DECLARE_TASKLET_OLD(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt);
1138
1139 void kgdb_schedule_breakpoint(void)
1140 {
1141         if (atomic_read(&kgdb_break_tasklet_var) ||
1142                 atomic_read(&kgdb_active) != -1 ||
1143                 atomic_read(&kgdb_setting_breakpoint))
1144                 return;
1145         atomic_inc(&kgdb_break_tasklet_var);
1146         tasklet_schedule(&kgdb_tasklet_breakpoint);
1147 }
1148 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
1149
1150 /**
1151  *      kgdb_register_io_module - register KGDB IO module
1152  *      @new_dbg_io_ops: the io ops vector
1153  *
1154  *      Register it with the KGDB core.
1155  */
1156 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1157 {
1158         struct kgdb_io *old_dbg_io_ops;
1159         int err;
1160
1161         spin_lock(&kgdb_registration_lock);
1162
1163         old_dbg_io_ops = dbg_io_ops;
1164         if (old_dbg_io_ops) {
1165                 if (!old_dbg_io_ops->deinit) {
1166                         spin_unlock(&kgdb_registration_lock);
1167
1168                         pr_err("KGDB I/O driver %s can't replace %s.\n",
1169                                 new_dbg_io_ops->name, old_dbg_io_ops->name);
1170                         return -EBUSY;
1171                 }
1172                 pr_info("Replacing I/O driver %s with %s\n",
1173                         old_dbg_io_ops->name, new_dbg_io_ops->name);
1174         }
1175
1176         if (new_dbg_io_ops->init) {
1177                 err = new_dbg_io_ops->init();
1178                 if (err) {
1179                         spin_unlock(&kgdb_registration_lock);
1180                         return err;
1181                 }
1182         }
1183
1184         dbg_io_ops = new_dbg_io_ops;
1185
1186         spin_unlock(&kgdb_registration_lock);
1187
1188         if (old_dbg_io_ops) {
1189                 old_dbg_io_ops->deinit();
1190                 return 0;
1191         }
1192
1193         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1194
1195         /* Arm KGDB now. */
1196         kgdb_register_callbacks();
1197
1198         if (kgdb_break_asap &&
1199             (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
1200                 kgdb_initial_breakpoint();
1201
1202         return 0;
1203 }
1204 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1205
1206 /**
1207  *      kkgdb_unregister_io_module - unregister KGDB IO module
1208  *      @old_dbg_io_ops: the io ops vector
1209  *
1210  *      Unregister it with the KGDB core.
1211  */
1212 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1213 {
1214         BUG_ON(kgdb_connected);
1215
1216         /*
1217          * KGDB is no longer able to communicate out, so
1218          * unregister our callbacks and reset state.
1219          */
1220         kgdb_unregister_callbacks();
1221
1222         spin_lock(&kgdb_registration_lock);
1223
1224         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1225         dbg_io_ops = NULL;
1226
1227         spin_unlock(&kgdb_registration_lock);
1228
1229         if (old_dbg_io_ops->deinit)
1230                 old_dbg_io_ops->deinit();
1231
1232         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1233                 old_dbg_io_ops->name);
1234 }
1235 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1236
1237 int dbg_io_get_char(void)
1238 {
1239         int ret = dbg_io_ops->read_char();
1240         if (ret == NO_POLL_CHAR)
1241                 return -1;
1242         if (!dbg_kdb_mode)
1243                 return ret;
1244         if (ret == 127)
1245                 return 8;
1246         return ret;
1247 }
1248
1249 /**
1250  * kgdb_breakpoint - generate breakpoint exception
1251  *
1252  * This function will generate a breakpoint exception.  It is used at the
1253  * beginning of a program to sync up with a debugger and can be used
1254  * otherwise as a quick means to stop program execution and "break" into
1255  * the debugger.
1256  */
1257 noinline void kgdb_breakpoint(void)
1258 {
1259         atomic_inc(&kgdb_setting_breakpoint);
1260         wmb(); /* Sync point before breakpoint */
1261         arch_kgdb_breakpoint();
1262         wmb(); /* Sync point after breakpoint */
1263         atomic_dec(&kgdb_setting_breakpoint);
1264 }
1265 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1266
1267 static int __init opt_kgdb_wait(char *str)
1268 {
1269         kgdb_break_asap = 1;
1270
1271         kdb_init(KDB_INIT_EARLY);
1272         if (kgdb_io_module_registered &&
1273             IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
1274                 kgdb_initial_breakpoint();
1275
1276         return 0;
1277 }
1278
1279 early_param("kgdbwait", opt_kgdb_wait);