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