kernel/debug/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
  63 static int kgdb_break_asap;
  64
  65 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  66
  67 /* kgdb_connected - Is a host GDB connected to us? */
  68 int                             kgdb_connected;
  69 EXPORT_SYMBOL_GPL(kgdb_connected);
  70
  71 /* All the KGDB handlers are installed */
  72 int                     kgdb_io_module_registered;
  73
  74 /* Guard for recursive entry */
  75 static int                      exception_level;
  76
  77 struct kgdb_io          *dbg_io_ops;
  78 static DEFINE_SPINLOCK(kgdb_registration_lock);
  79
  80 /* Action for the reboot notifier, a global allow kdb to change it */
  81 static int kgdbreboot;
  82 /* kgdb console driver is loaded */
  83 static int kgdb_con_registered;
  84 /* determine if kgdb console output should be used */
  85 static int kgdb_use_con;
  86 /* Flag for alternate operations for early debugging */
  87 bool dbg_is_early = true;
  88 /* Next cpu to become the master debug core */
  89 int dbg_switch_cpu;
  90
  91 /* Use kdb or gdbserver mode */
  92 int dbg_kdb_mode = 1;
  93
  94 module_param(kgdb_use_con, int, 0644);
  95 module_param(kgdbreboot, int, 0644);
  96
  97 /*
  98  * Holds information about breakpoints in a kernel. These breakpoints are
  99  * added and removed by gdb.
 100  */
 101 static 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  */
 108 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 109 EXPORT_SYMBOL_GPL(kgdb_active);
 110 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 111 static 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  */
 117 static atomic_t                 masters_in_kgdb;
 118 static atomic_t                 slaves_in_kgdb;
 119 atomic_t                        kgdb_setting_breakpoint;
 120
 121 struct task_struct              *kgdb_usethread;
 122 struct task_struct              *kgdb_contthread;
 123
 124 int                             kgdb_single_step;
 125 static pid_t                    kgdb_sstep_pid;
 126
 127 /* to keep track of the CPU which is doing the single stepping*/
 128 atomic_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  */
 137 static int kgdb_do_roundup = 1;
 138
 139 static int __init opt_nokgdbroundup(char *str)
 140 {
 141         kgdb_do_roundup = 0;
 142
 143         return 0;
 144 }
 145
 146 early_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  */
 156 int __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 }
 168 NOKPROBE_SYMBOL(kgdb_arch_set_breakpoint);
 169
 170 int __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 }
 175 NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
 176
 177 int __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
 201 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 202 {
 203         return instruction_pointer(regs);
 204 }
 205 NOKPROBE_SYMBOL(kgdb_arch_pc);
 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 NOKPROBE_SYMBOL(kgdb_skipexception);
 217
 218 #ifdef CONFIG_SMP
 219
 220 /*
 221  * Default (weak) implementation for kgdb_roundup_cpus
 222  */
 223
 224 void __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 }
 236 NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 237
 238 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
 239         CSD_INIT(kgdb_call_nmi_hook, NULL);
 240
 241 void __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 }
 272 NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 273
 274 #endif
 275
 276 /*
 277  * Some architectures need cache flushes when we set/clear a
 278  * breakpoint:
 279  */
 280 static 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 }
 288 NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
 289
 290 /*
 291  * SW breakpoint management:
 292  */
 293 int 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 }
 316 NOKPROBE_SYMBOL(dbg_activate_sw_breakpoints);
 317
 318 int 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
 359 int 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 }
 380 NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
 381
 382 int 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
 396 int 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
 408 int 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
 420 int 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);
 433 setundefined:
 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
 444 void 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
 456 void 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  */
 495 static 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 }
 513 NOKPROBE_SYMBOL(kgdb_io_ready);
 514
 515 static 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 }
 561 NOKPROBE_SYMBOL(kgdb_reenter_check);
 562
 563 static void dbg_touch_watchdogs(void)
 564 {
 565         touch_softlockup_watchdog_sync();
 566         clocksource_touch_watchdog();
 567         rcu_cpu_stall_reset();
 568 }
 569 NOKPROBE_SYMBOL(dbg_touch_watchdogs);
 570
 571 static 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
 593 acquirelock:
 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) {
 621 cpu_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 {
 637 return_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) {
 736 cpu_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
 797 kgdb_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 }
 826 NOKPROBE_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  */
 835 int
 836 kgdb_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         int ret = 0;
 841
 842         if (arch_kgdb_ops.enable_nmi)
 843                 arch_kgdb_ops.enable_nmi(0);
 844         /*
 845          * Avoid entering the debugger if we were triggered due to an oops
 846          * but panic_timeout indicates the system should automatically
 847          * reboot on panic. We don't want to get stuck waiting for input
 848          * on such systems, especially if its "just" an oops.
 849          */
 850         if (signo != SIGTRAP && panic_timeout)
 851                 return 1;
 852
 853         memset(ks, 0, sizeof(struct kgdb_state));
 854         ks->cpu                 = raw_smp_processor_id();
 855         ks->ex_vector           = evector;
 856         ks->signo               = signo;
 857         ks->err_code            = ecode;
 858         ks->linux_regs          = regs;
 859
 860         if (kgdb_reenter_check(ks))
 861                 goto out; /* Ouch, double exception ! */
 862         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 863                 goto out;
 864
 865         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 866 out:
 867         if (arch_kgdb_ops.enable_nmi)
 868                 arch_kgdb_ops.enable_nmi(1);
 869         return ret;
 870 }
 871 NOKPROBE_SYMBOL(kgdb_handle_exception);
 872
 873 /*
 874  * GDB places a breakpoint at this function to know dynamically loaded objects.
 875  */
 876 static int module_event(struct notifier_block *self, unsigned long val,
 877         void *data)
 878 {
 879         return 0;
 880 }
 881
 882 static struct notifier_block dbg_module_load_nb = {
 883         .notifier_call  = module_event,
 884 };
 885
 886 int kgdb_nmicallback(int cpu, void *regs)
 887 {
 888 #ifdef CONFIG_SMP
 889         struct kgdb_state kgdb_var;
 890         struct kgdb_state *ks = &kgdb_var;
 891
 892         kgdb_info[cpu].rounding_up = false;
 893
 894         memset(ks, 0, sizeof(struct kgdb_state));
 895         ks->cpu                 = cpu;
 896         ks->linux_regs          = regs;
 897
 898         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 899                         raw_spin_is_locked(&dbg_master_lock)) {
 900                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 901                 return 0;
 902         }
 903 #endif
 904         return 1;
 905 }
 906 NOKPROBE_SYMBOL(kgdb_nmicallback);
 907
 908 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 909                                                         atomic_t *send_ready)
 910 {
 911 #ifdef CONFIG_SMP
 912         if (!kgdb_io_ready(0) || !send_ready)
 913                 return 1;
 914
 915         if (kgdb_info[cpu].enter_kgdb == 0) {
 916                 struct kgdb_state kgdb_var;
 917                 struct kgdb_state *ks = &kgdb_var;
 918
 919                 memset(ks, 0, sizeof(struct kgdb_state));
 920                 ks->cpu                 = cpu;
 921                 ks->ex_vector           = trapnr;
 922                 ks->signo               = SIGTRAP;
 923                 ks->err_code            = err_code;
 924                 ks->linux_regs          = regs;
 925                 ks->send_ready          = send_ready;
 926                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 927                 return 0;
 928         }
 929 #endif
 930         return 1;
 931 }
 932 NOKPROBE_SYMBOL(kgdb_nmicallin);
 933
 934 static void kgdb_console_write(struct console *co, const char *s,
 935    unsigned count)
 936 {
 937         unsigned long flags;
 938
 939         /* If we're debugging, or KGDB has not connected, don't try
 940          * and print. */
 941         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 942                 return;
 943
 944         local_irq_save(flags);
 945         gdbstub_msg_write(s, count);
 946         local_irq_restore(flags);
 947 }
 948
 949 static struct console kgdbcons = {
 950         .name           = "kgdb",
 951         .write          = kgdb_console_write,
 952         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 953         .index          = -1,
 954 };
 955
 956 static int __init opt_kgdb_con(char *str)
 957 {
 958         kgdb_use_con = 1;
 959
 960         if (kgdb_io_module_registered && !kgdb_con_registered) {
 961                 register_console(&kgdbcons);
 962                 kgdb_con_registered = 1;
 963         }
 964
 965         return 0;
 966 }
 967
 968 early_param("kgdbcon", opt_kgdb_con);
 969
 970 #ifdef CONFIG_MAGIC_SYSRQ
 971 static void sysrq_handle_dbg(int key)
 972 {
 973         if (!dbg_io_ops) {
 974                 pr_crit("ERROR: No KGDB I/O module available\n");
 975                 return;
 976         }
 977         if (!kgdb_connected) {
 978 #ifdef CONFIG_KGDB_KDB
 979                 if (!dbg_kdb_mode)
 980                         pr_crit("KGDB or $3#33 for KDB\n");
 981 #else
 982                 pr_crit("Entering KGDB\n");
 983 #endif
 984         }
 985
 986         kgdb_breakpoint();
 987 }
 988
 989 static const struct sysrq_key_op sysrq_dbg_op = {
 990         .handler        = sysrq_handle_dbg,
 991         .help_msg       = "debug(g)",
 992         .action_msg     = "DEBUG",
 993 };
 994 #endif
 995
 996 void kgdb_panic(const char *msg)
 997 {
 998         if (!kgdb_io_module_registered)
 999                 return;
1000
1001         /*
1002          * We don't want to get stuck waiting for input from user if
1003          * "panic_timeout" indicates the system should automatically
1004          * reboot on panic.
1005          */
1006         if (panic_timeout)
1007                 return;
1008
1009         if (dbg_kdb_mode)
1010                 kdb_printf("PANIC: %s\n", msg);
1011
1012         kgdb_breakpoint();
1013 }
1014
1015 static void kgdb_initial_breakpoint(void)
1016 {
1017         kgdb_break_asap = 0;
1018
1019         pr_crit("Waiting for connection from remote gdb...\n");
1020         kgdb_breakpoint();
1021 }
1022
1023 void __weak kgdb_arch_late(void)
1024 {
1025 }
1026
1027 void __init dbg_late_init(void)
1028 {
1029         dbg_is_early = false;
1030         if (kgdb_io_module_registered)
1031                 kgdb_arch_late();
1032         kdb_init(KDB_INIT_FULL);
1033
1034         if (kgdb_io_module_registered && kgdb_break_asap)
1035                 kgdb_initial_breakpoint();
1036 }
1037
1038 static int
1039 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
1040 {
1041         /*
1042          * Take the following action on reboot notify depending on value:
1043          *    1 == Enter debugger
1044          *    0 == [the default] detach debug client
1045          *   -1 == Do nothing... and use this until the board resets
1046          */
1047         switch (kgdbreboot) {
1048         case 1:
1049                 kgdb_breakpoint();
1050                 goto done;
1051         case -1:
1052                 goto done;
1053         }
1054         if (!dbg_kdb_mode)
1055                 gdbstub_exit(code);
1056 done:
1057         return NOTIFY_DONE;
1058 }
1059
1060 static struct notifier_block dbg_reboot_notifier = {
1061         .notifier_call          = dbg_notify_reboot,
1062         .next                   = NULL,
1063         .priority               = INT_MAX,
1064 };
1065
1066 static void kgdb_register_callbacks(void)
1067 {
1068         if (!kgdb_io_module_registered) {
1069                 kgdb_io_module_registered = 1;
1070                 kgdb_arch_init();
1071                 if (!dbg_is_early)
1072                         kgdb_arch_late();
1073                 register_module_notifier(&dbg_module_load_nb);
1074                 register_reboot_notifier(&dbg_reboot_notifier);
1075 #ifdef CONFIG_MAGIC_SYSRQ
1076                 register_sysrq_key('g', &sysrq_dbg_op);
1077 #endif
1078                 if (kgdb_use_con && !kgdb_con_registered) {
1079                         register_console(&kgdbcons);
1080                         kgdb_con_registered = 1;
1081                 }
1082         }
1083 }
1084
1085 static void kgdb_unregister_callbacks(void)
1086 {
1087         /*
1088          * When this routine is called KGDB should unregister from
1089          * handlers and clean up, making sure it is not handling any
1090          * break exceptions at the time.
1091          */
1092         if (kgdb_io_module_registered) {
1093                 kgdb_io_module_registered = 0;
1094                 unregister_reboot_notifier(&dbg_reboot_notifier);
1095                 unregister_module_notifier(&dbg_module_load_nb);
1096                 kgdb_arch_exit();
1097 #ifdef CONFIG_MAGIC_SYSRQ
1098                 unregister_sysrq_key('g', &sysrq_dbg_op);
1099 #endif
1100                 if (kgdb_con_registered) {
1101                         unregister_console(&kgdbcons);
1102                         kgdb_con_registered = 0;
1103                 }
1104         }
1105 }
1106
1107 /**
1108  *      kgdb_register_io_module - register KGDB IO module
1109  *      @new_dbg_io_ops: the io ops vector
1110  *
1111  *      Register it with the KGDB core.
1112  */
1113 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1114 {
1115         struct kgdb_io *old_dbg_io_ops;
1116         int err;
1117
1118         spin_lock(&kgdb_registration_lock);
1119
1120         old_dbg_io_ops = dbg_io_ops;
1121         if (old_dbg_io_ops) {
1122                 if (!old_dbg_io_ops->deinit) {
1123                         spin_unlock(&kgdb_registration_lock);
1124
1125                         pr_err("KGDB I/O driver %s can't replace %s.\n",
1126                                 new_dbg_io_ops->name, old_dbg_io_ops->name);
1127                         return -EBUSY;
1128                 }
1129                 pr_info("Replacing I/O driver %s with %s\n",
1130                         old_dbg_io_ops->name, new_dbg_io_ops->name);
1131         }
1132
1133         if (new_dbg_io_ops->init) {
1134                 err = new_dbg_io_ops->init();
1135                 if (err) {
1136                         spin_unlock(&kgdb_registration_lock);
1137                         return err;
1138                 }
1139         }
1140
1141         dbg_io_ops = new_dbg_io_ops;
1142
1143         spin_unlock(&kgdb_registration_lock);
1144
1145         if (old_dbg_io_ops) {
1146                 old_dbg_io_ops->deinit();
1147                 return 0;
1148         }
1149
1150         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1151
1152         /* Arm KGDB now. */
1153         kgdb_register_callbacks();
1154
1155         if (kgdb_break_asap &&
1156             (!dbg_is_early || IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG)))
1157                 kgdb_initial_breakpoint();
1158
1159         return 0;
1160 }
1161 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1162
1163 /**
1164  *      kgdb_unregister_io_module - unregister KGDB IO module
1165  *      @old_dbg_io_ops: the io ops vector
1166  *
1167  *      Unregister it with the KGDB core.
1168  */
1169 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1170 {
1171         BUG_ON(kgdb_connected);
1172
1173         /*
1174          * KGDB is no longer able to communicate out, so
1175          * unregister our callbacks and reset state.
1176          */
1177         kgdb_unregister_callbacks();
1178
1179         spin_lock(&kgdb_registration_lock);
1180
1181         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1182         dbg_io_ops = NULL;
1183
1184         spin_unlock(&kgdb_registration_lock);
1185
1186         if (old_dbg_io_ops->deinit)
1187                 old_dbg_io_ops->deinit();
1188
1189         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1190                 old_dbg_io_ops->name);
1191 }
1192 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1193
1194 int dbg_io_get_char(void)
1195 {
1196         int ret = dbg_io_ops->read_char();
1197         if (ret == NO_POLL_CHAR)
1198                 return -1;
1199         if (!dbg_kdb_mode)
1200                 return ret;
1201         if (ret == 127)
1202                 return 8;
1203         return ret;
1204 }
1205
1206 /**
1207  * kgdb_breakpoint - generate breakpoint exception
1208  *
1209  * This function will generate a breakpoint exception.  It is used at the
1210  * beginning of a program to sync up with a debugger and can be used
1211  * otherwise as a quick means to stop program execution and "break" into
1212  * the debugger.
1213  */
1214 noinline void kgdb_breakpoint(void)
1215 {
1216         atomic_inc(&kgdb_setting_breakpoint);
1217         wmb(); /* Sync point before breakpoint */
1218         arch_kgdb_breakpoint();
1219         wmb(); /* Sync point after breakpoint */
1220         atomic_dec(&kgdb_setting_breakpoint);
1221 }
1222 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1223
1224 static int __init opt_kgdb_wait(char *str)
1225 {
1226         kgdb_break_asap = 1;
1227
1228         kdb_init(KDB_INIT_EARLY);
1229         if (kgdb_io_module_registered &&
1230             IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
1231                 kgdb_initial_breakpoint();
1232
1233         return 0;
1234 }
1235
1236 early_param("kgdbwait", opt_kgdb_wait);