drivers/tty/sysrq.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *      Linux Magic System Request Key Hacks
   4  *
   5  *      (c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   6  *      based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
   7  *
   8  *      (c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
   9  *      overhauled to use key registration
  10  *      based upon discusions in irc://irc.openprojects.net/#kernelnewbies
  11  *
  12  *      Copyright (c) 2010 Dmitry Torokhov
  13  *      Input handler conversion
  14  */
  15
  16 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  17
  18 #include <linux/sched/signal.h>
  19 #include <linux/sched/rt.h>
  20 #include <linux/sched/debug.h>
  21 #include <linux/sched/task.h>
  22 #include <linux/interrupt.h>
  23 #include <linux/mm.h>
  24 #include <linux/fs.h>
  25 #include <linux/mount.h>
  26 #include <linux/kdev_t.h>
  27 #include <linux/major.h>
  28 #include <linux/reboot.h>
  29 #include <linux/sysrq.h>
  30 #include <linux/kbd_kern.h>
  31 #include <linux/proc_fs.h>
  32 #include <linux/nmi.h>
  33 #include <linux/quotaops.h>
  34 #include <linux/perf_event.h>
  35 #include <linux/kernel.h>
  36 #include <linux/module.h>
  37 #include <linux/suspend.h>
  38 #include <linux/writeback.h>
  39 #include <linux/swap.h>
  40 #include <linux/spinlock.h>
  41 #include <linux/vt_kern.h>
  42 #include <linux/workqueue.h>
  43 #include <linux/hrtimer.h>
  44 #include <linux/oom.h>
  45 #include <linux/slab.h>
  46 #include <linux/input.h>
  47 #include <linux/uaccess.h>
  48 #include <linux/moduleparam.h>
  49 #include <linux/jiffies.h>
  50 #include <linux/syscalls.h>
  51 #include <linux/of.h>
  52 #include <linux/rcupdate.h>
  53
  54 #include <asm/ptrace.h>
  55 #include <asm/irq_regs.h>
  56
  57 /* Whether we react on sysrq keys or just ignore them */
  58 static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
  59 static bool __read_mostly sysrq_always_enabled;
  60
  61 static bool sysrq_on(void)
  62 {
  63         return sysrq_enabled || sysrq_always_enabled;
  64 }
  65
  66 /**
  67  * sysrq_mask - Getter for sysrq_enabled mask.
  68  *
  69  * Return: 1 if sysrq is always enabled, enabled sysrq_key_op mask otherwise.
  70  */
  71 int sysrq_mask(void)
  72 {
  73         if (sysrq_always_enabled)
  74                 return 1;
  75         return sysrq_enabled;
  76 }
  77
  78 /*
  79  * A value of 1 means 'all', other nonzero values are an op mask:
  80  */
  81 static bool sysrq_on_mask(int mask)
  82 {
  83         return sysrq_always_enabled ||
  84                sysrq_enabled == 1 ||
  85                (sysrq_enabled & mask);
  86 }
  87
  88 static int __init sysrq_always_enabled_setup(char *str)
  89 {
  90         sysrq_always_enabled = true;
  91         pr_info("sysrq always enabled.\n");
  92
  93         return 1;
  94 }
  95
  96 __setup("sysrq_always_enabled", sysrq_always_enabled_setup);
  97
  98
  99 static void sysrq_handle_loglevel(int key)
 100 {
 101         int i;
 102
 103         i = key - '0';
 104         console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
 105         pr_info("Loglevel set to %d\n", i);
 106         console_loglevel = i;
 107 }
 108 static struct sysrq_key_op sysrq_loglevel_op = {
 109         .handler        = sysrq_handle_loglevel,
 110         .help_msg       = "loglevel(0-9)",
 111         .action_msg     = "Changing Loglevel",
 112         .enable_mask    = SYSRQ_ENABLE_LOG,
 113 };
 114
 115 #ifdef CONFIG_VT
 116 static void sysrq_handle_SAK(int key)
 117 {
 118         struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
 119         schedule_work(SAK_work);
 120 }
 121 static struct sysrq_key_op sysrq_SAK_op = {
 122         .handler        = sysrq_handle_SAK,
 123         .help_msg       = "sak(k)",
 124         .action_msg     = "SAK",
 125         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
 126 };
 127 #else
 128 #define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
 129 #endif
 130
 131 #ifdef CONFIG_VT
 132 static void sysrq_handle_unraw(int key)
 133 {
 134         vt_reset_unicode(fg_console);
 135 }
 136
 137 static struct sysrq_key_op sysrq_unraw_op = {
 138         .handler        = sysrq_handle_unraw,
 139         .help_msg       = "unraw(r)",
 140         .action_msg     = "Keyboard mode set to system default",
 141         .enable_mask    = SYSRQ_ENABLE_KEYBOARD,
 142 };
 143 #else
 144 #define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
 145 #endif /* CONFIG_VT */
 146
 147 static void sysrq_handle_crash(int key)
 148 {
 149         /* release the RCU read lock before crashing */
 150         rcu_read_unlock();
 151
 152         panic("sysrq triggered crash\n");
 153 }
 154 static struct sysrq_key_op sysrq_crash_op = {
 155         .handler        = sysrq_handle_crash,
 156         .help_msg       = "crash(c)",
 157         .action_msg     = "Trigger a crash",
 158         .enable_mask    = SYSRQ_ENABLE_DUMP,
 159 };
 160
 161 static void sysrq_handle_reboot(int key)
 162 {
 163         lockdep_off();
 164         local_irq_enable();
 165         emergency_restart();
 166 }
 167 static struct sysrq_key_op sysrq_reboot_op = {
 168         .handler        = sysrq_handle_reboot,
 169         .help_msg       = "reboot(b)",
 170         .action_msg     = "Resetting",
 171         .enable_mask    = SYSRQ_ENABLE_BOOT,
 172 };
 173
 174 static void sysrq_handle_sync(int key)
 175 {
 176         emergency_sync();
 177 }
 178 static struct sysrq_key_op sysrq_sync_op = {
 179         .handler        = sysrq_handle_sync,
 180         .help_msg       = "sync(s)",
 181         .action_msg     = "Emergency Sync",
 182         .enable_mask    = SYSRQ_ENABLE_SYNC,
 183 };
 184
 185 static void sysrq_handle_show_timers(int key)
 186 {
 187         sysrq_timer_list_show();
 188 }
 189
 190 static struct sysrq_key_op sysrq_show_timers_op = {
 191         .handler        = sysrq_handle_show_timers,
 192         .help_msg       = "show-all-timers(q)",
 193         .action_msg     = "Show clockevent devices & pending hrtimers (no others)",
 194 };
 195
 196 static void sysrq_handle_mountro(int key)
 197 {
 198         emergency_remount();
 199 }
 200 static struct sysrq_key_op sysrq_mountro_op = {
 201         .handler        = sysrq_handle_mountro,
 202         .help_msg       = "unmount(u)",
 203         .action_msg     = "Emergency Remount R/O",
 204         .enable_mask    = SYSRQ_ENABLE_REMOUNT,
 205 };
 206
 207 #ifdef CONFIG_LOCKDEP
 208 static void sysrq_handle_showlocks(int key)
 209 {
 210         debug_show_all_locks();
 211 }
 212
 213 static struct sysrq_key_op sysrq_showlocks_op = {
 214         .handler        = sysrq_handle_showlocks,
 215         .help_msg       = "show-all-locks(d)",
 216         .action_msg     = "Show Locks Held",
 217 };
 218 #else
 219 #define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
 220 #endif
 221
 222 #ifdef CONFIG_SMP
 223 static DEFINE_RAW_SPINLOCK(show_lock);
 224
 225 static void showacpu(void *dummy)
 226 {
 227         unsigned long flags;
 228
 229         /* Idle CPUs have no interesting backtrace. */
 230         if (idle_cpu(smp_processor_id()))
 231                 return;
 232
 233         raw_spin_lock_irqsave(&show_lock, flags);
 234         pr_info("CPU%d:\n", smp_processor_id());
 235         show_stack(NULL, NULL);
 236         raw_spin_unlock_irqrestore(&show_lock, flags);
 237 }
 238
 239 static void sysrq_showregs_othercpus(struct work_struct *dummy)
 240 {
 241         smp_call_function(showacpu, NULL, 0);
 242 }
 243
 244 static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
 245
 246 static void sysrq_handle_showallcpus(int key)
 247 {
 248         /*
 249          * Fall back to the workqueue based printing if the
 250          * backtrace printing did not succeed or the
 251          * architecture has no support for it:
 252          */
 253         if (!trigger_all_cpu_backtrace()) {
 254                 struct pt_regs *regs = NULL;
 255
 256                 if (in_irq())
 257                         regs = get_irq_regs();
 258                 if (regs) {
 259                         pr_info("CPU%d:\n", smp_processor_id());
 260                         show_regs(regs);
 261                 }
 262                 schedule_work(&sysrq_showallcpus);
 263         }
 264 }
 265
 266 static struct sysrq_key_op sysrq_showallcpus_op = {
 267         .handler        = sysrq_handle_showallcpus,
 268         .help_msg       = "show-backtrace-all-active-cpus(l)",
 269         .action_msg     = "Show backtrace of all active CPUs",
 270         .enable_mask    = SYSRQ_ENABLE_DUMP,
 271 };
 272 #endif
 273
 274 static void sysrq_handle_showregs(int key)
 275 {
 276         struct pt_regs *regs = NULL;
 277
 278         if (in_irq())
 279                 regs = get_irq_regs();
 280         if (regs)
 281                 show_regs(regs);
 282         perf_event_print_debug();
 283 }
 284 static struct sysrq_key_op sysrq_showregs_op = {
 285         .handler        = sysrq_handle_showregs,
 286         .help_msg       = "show-registers(p)",
 287         .action_msg     = "Show Regs",
 288         .enable_mask    = SYSRQ_ENABLE_DUMP,
 289 };
 290
 291 static void sysrq_handle_showstate(int key)
 292 {
 293         show_state();
 294         show_workqueue_state();
 295 }
 296 static struct sysrq_key_op sysrq_showstate_op = {
 297         .handler        = sysrq_handle_showstate,
 298         .help_msg       = "show-task-states(t)",
 299         .action_msg     = "Show State",
 300         .enable_mask    = SYSRQ_ENABLE_DUMP,
 301 };
 302
 303 static void sysrq_handle_showstate_blocked(int key)
 304 {
 305         show_state_filter(TASK_UNINTERRUPTIBLE);
 306 }
 307 static struct sysrq_key_op sysrq_showstate_blocked_op = {
 308         .handler        = sysrq_handle_showstate_blocked,
 309         .help_msg       = "show-blocked-tasks(w)",
 310         .action_msg     = "Show Blocked State",
 311         .enable_mask    = SYSRQ_ENABLE_DUMP,
 312 };
 313
 314 #ifdef CONFIG_TRACING
 315 #include <linux/ftrace.h>
 316
 317 static void sysrq_ftrace_dump(int key)
 318 {
 319         ftrace_dump(DUMP_ALL);
 320 }
 321 static struct sysrq_key_op sysrq_ftrace_dump_op = {
 322         .handler        = sysrq_ftrace_dump,
 323         .help_msg       = "dump-ftrace-buffer(z)",
 324         .action_msg     = "Dump ftrace buffer",
 325         .enable_mask    = SYSRQ_ENABLE_DUMP,
 326 };
 327 #else
 328 #define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
 329 #endif
 330
 331 static void sysrq_handle_showmem(int key)
 332 {
 333         show_mem(0, NULL);
 334 }
 335 static struct sysrq_key_op sysrq_showmem_op = {
 336         .handler        = sysrq_handle_showmem,
 337         .help_msg       = "show-memory-usage(m)",
 338         .action_msg     = "Show Memory",
 339         .enable_mask    = SYSRQ_ENABLE_DUMP,
 340 };
 341
 342 /*
 343  * Signal sysrq helper function.  Sends a signal to all user processes.
 344  */
 345 static void send_sig_all(int sig)
 346 {
 347         struct task_struct *p;
 348
 349         read_lock(&tasklist_lock);
 350         for_each_process(p) {
 351                 if (p->flags & PF_KTHREAD)
 352                         continue;
 353                 if (is_global_init(p))
 354                         continue;
 355
 356                 do_send_sig_info(sig, SEND_SIG_PRIV, p, PIDTYPE_MAX);
 357         }
 358         read_unlock(&tasklist_lock);
 359 }
 360
 361 static void sysrq_handle_term(int key)
 362 {
 363         send_sig_all(SIGTERM);
 364         console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
 365 }
 366 static struct sysrq_key_op sysrq_term_op = {
 367         .handler        = sysrq_handle_term,
 368         .help_msg       = "terminate-all-tasks(e)",
 369         .action_msg     = "Terminate All Tasks",
 370         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 371 };
 372
 373 static void moom_callback(struct work_struct *ignored)
 374 {
 375         const gfp_t gfp_mask = GFP_KERNEL;
 376         struct oom_control oc = {
 377                 .zonelist = node_zonelist(first_memory_node, gfp_mask),
 378                 .nodemask = NULL,
 379                 .memcg = NULL,
 380                 .gfp_mask = gfp_mask,
 381                 .order = -1,
 382         };
 383
 384         mutex_lock(&oom_lock);
 385         if (!out_of_memory(&oc))
 386                 pr_info("OOM request ignored. No task eligible\n");
 387         mutex_unlock(&oom_lock);
 388 }
 389
 390 static DECLARE_WORK(moom_work, moom_callback);
 391
 392 static void sysrq_handle_moom(int key)
 393 {
 394         schedule_work(&moom_work);
 395 }
 396 static struct sysrq_key_op sysrq_moom_op = {
 397         .handler        = sysrq_handle_moom,
 398         .help_msg       = "memory-full-oom-kill(f)",
 399         .action_msg     = "Manual OOM execution",
 400         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 401 };
 402
 403 #ifdef CONFIG_BLOCK
 404 static void sysrq_handle_thaw(int key)
 405 {
 406         emergency_thaw_all();
 407 }
 408 static struct sysrq_key_op sysrq_thaw_op = {
 409         .handler        = sysrq_handle_thaw,
 410         .help_msg       = "thaw-filesystems(j)",
 411         .action_msg     = "Emergency Thaw of all frozen filesystems",
 412         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 413 };
 414 #endif
 415
 416 static void sysrq_handle_kill(int key)
 417 {
 418         send_sig_all(SIGKILL);
 419         console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
 420 }
 421 static struct sysrq_key_op sysrq_kill_op = {
 422         .handler        = sysrq_handle_kill,
 423         .help_msg       = "kill-all-tasks(i)",
 424         .action_msg     = "Kill All Tasks",
 425         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 426 };
 427
 428 static void sysrq_handle_unrt(int key)
 429 {
 430         normalize_rt_tasks();
 431 }
 432 static struct sysrq_key_op sysrq_unrt_op = {
 433         .handler        = sysrq_handle_unrt,
 434         .help_msg       = "nice-all-RT-tasks(n)",
 435         .action_msg     = "Nice All RT Tasks",
 436         .enable_mask    = SYSRQ_ENABLE_RTNICE,
 437 };
 438
 439 /* Key Operations table and lock */
 440 static DEFINE_SPINLOCK(sysrq_key_table_lock);
 441
 442 static struct sysrq_key_op *sysrq_key_table[36] = {
 443         &sysrq_loglevel_op,             /* 0 */
 444         &sysrq_loglevel_op,             /* 1 */
 445         &sysrq_loglevel_op,             /* 2 */
 446         &sysrq_loglevel_op,             /* 3 */
 447         &sysrq_loglevel_op,             /* 4 */
 448         &sysrq_loglevel_op,             /* 5 */
 449         &sysrq_loglevel_op,             /* 6 */
 450         &sysrq_loglevel_op,             /* 7 */
 451         &sysrq_loglevel_op,             /* 8 */
 452         &sysrq_loglevel_op,             /* 9 */
 453
 454         /*
 455          * a: Don't use for system provided sysrqs, it is handled specially on
 456          * sparc and will never arrive.
 457          */
 458         NULL,                           /* a */
 459         &sysrq_reboot_op,               /* b */
 460         &sysrq_crash_op,                /* c */
 461         &sysrq_showlocks_op,            /* d */
 462         &sysrq_term_op,                 /* e */
 463         &sysrq_moom_op,                 /* f */
 464         /* g: May be registered for the kernel debugger */
 465         NULL,                           /* g */
 466         NULL,                           /* h - reserved for help */
 467         &sysrq_kill_op,                 /* i */
 468 #ifdef CONFIG_BLOCK
 469         &sysrq_thaw_op,                 /* j */
 470 #else
 471         NULL,                           /* j */
 472 #endif
 473         &sysrq_SAK_op,                  /* k */
 474 #ifdef CONFIG_SMP
 475         &sysrq_showallcpus_op,          /* l */
 476 #else
 477         NULL,                           /* l */
 478 #endif
 479         &sysrq_showmem_op,              /* m */
 480         &sysrq_unrt_op,                 /* n */
 481         /* o: This will often be registered as 'Off' at init time */
 482         NULL,                           /* o */
 483         &sysrq_showregs_op,             /* p */
 484         &sysrq_show_timers_op,          /* q */
 485         &sysrq_unraw_op,                /* r */
 486         &sysrq_sync_op,                 /* s */
 487         &sysrq_showstate_op,            /* t */
 488         &sysrq_mountro_op,              /* u */
 489         /* v: May be registered for frame buffer console restore */
 490         NULL,                           /* v */
 491         &sysrq_showstate_blocked_op,    /* w */
 492         /* x: May be registered on mips for TLB dump */
 493         /* x: May be registered on ppc/powerpc for xmon */
 494         /* x: May be registered on sparc64 for global PMU dump */
 495         NULL,                           /* x */
 496         /* y: May be registered on sparc64 for global register dump */
 497         NULL,                           /* y */
 498         &sysrq_ftrace_dump_op,          /* z */
 499 };
 500
 501 /* key2index calculation, -1 on invalid index */
 502 static int sysrq_key_table_key2index(int key)
 503 {
 504         int retval;
 505
 506         if ((key >= '0') && (key <= '9'))
 507                 retval = key - '0';
 508         else if ((key >= 'a') && (key <= 'z'))
 509                 retval = key + 10 - 'a';
 510         else
 511                 retval = -1;
 512         return retval;
 513 }
 514
 515 /*
 516  * get and put functions for the table, exposed to modules.
 517  */
 518 struct sysrq_key_op *__sysrq_get_key_op(int key)
 519 {
 520         struct sysrq_key_op *op_p = NULL;
 521         int i;
 522
 523         i = sysrq_key_table_key2index(key);
 524         if (i != -1)
 525                 op_p = sysrq_key_table[i];
 526
 527         return op_p;
 528 }
 529
 530 static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
 531 {
 532         int i = sysrq_key_table_key2index(key);
 533
 534         if (i != -1)
 535                 sysrq_key_table[i] = op_p;
 536 }
 537
 538 void __handle_sysrq(int key, bool check_mask)
 539 {
 540         struct sysrq_key_op *op_p;
 541         int orig_log_level;
 542         int orig_suppress_printk;
 543         int i;
 544
 545         orig_suppress_printk = suppress_printk;
 546         suppress_printk = 0;
 547
 548         rcu_sysrq_start();
 549         rcu_read_lock();
 550         /*
 551          * Raise the apparent loglevel to maximum so that the sysrq header
 552          * is shown to provide the user with positive feedback.  We do not
 553          * simply emit this at KERN_EMERG as that would change message
 554          * routing in the consumers of /proc/kmsg.
 555          */
 556         orig_log_level = console_loglevel;
 557         console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
 558
 559         op_p = __sysrq_get_key_op(key);
 560         if (op_p) {
 561                 /*
 562                  * Should we check for enabled operations (/proc/sysrq-trigger
 563                  * should not) and is the invoked operation enabled?
 564                  */
 565                 if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
 566                         pr_info("%s\n", op_p->action_msg);
 567                         console_loglevel = orig_log_level;
 568                         op_p->handler(key);
 569                 } else {
 570                         pr_info("This sysrq operation is disabled.\n");
 571                         console_loglevel = orig_log_level;
 572                 }
 573         } else {
 574                 pr_info("HELP : ");
 575                 /* Only print the help msg once per handler */
 576                 for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
 577                         if (sysrq_key_table[i]) {
 578                                 int j;
 579
 580                                 for (j = 0; sysrq_key_table[i] !=
 581                                                 sysrq_key_table[j]; j++)
 582                                         ;
 583                                 if (j != i)
 584                                         continue;
 585                                 pr_cont("%s ", sysrq_key_table[i]->help_msg);
 586                         }
 587                 }
 588                 pr_cont("\n");
 589                 console_loglevel = orig_log_level;
 590         }
 591         rcu_read_unlock();
 592         rcu_sysrq_end();
 593
 594         suppress_printk = orig_suppress_printk;
 595 }
 596
 597 void handle_sysrq(int key)
 598 {
 599         if (sysrq_on())
 600                 __handle_sysrq(key, true);
 601 }
 602 EXPORT_SYMBOL(handle_sysrq);
 603
 604 #ifdef CONFIG_INPUT
 605 static int sysrq_reset_downtime_ms;
 606
 607 /* Simple translation table for the SysRq keys */
 608 static const unsigned char sysrq_xlate[KEY_CNT] =
 609         "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
 610         "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
 611         "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
 612         "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
 613         "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
 614         "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
 615         "\r\000/";                                      /* 0x60 - 0x6f */
 616
 617 struct sysrq_state {
 618         struct input_handle handle;
 619         struct work_struct reinject_work;
 620         unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
 621         unsigned int alt;
 622         unsigned int alt_use;
 623         bool active;
 624         bool need_reinject;
 625         bool reinjecting;
 626
 627         /* reset sequence handling */
 628         bool reset_canceled;
 629         bool reset_requested;
 630         unsigned long reset_keybit[BITS_TO_LONGS(KEY_CNT)];
 631         int reset_seq_len;
 632         int reset_seq_cnt;
 633         int reset_seq_version;
 634         struct timer_list keyreset_timer;
 635 };
 636
 637 #define SYSRQ_KEY_RESET_MAX     20 /* Should be plenty */
 638 static unsigned short sysrq_reset_seq[SYSRQ_KEY_RESET_MAX];
 639 static unsigned int sysrq_reset_seq_len;
 640 static unsigned int sysrq_reset_seq_version = 1;
 641
 642 static void sysrq_parse_reset_sequence(struct sysrq_state *state)
 643 {
 644         int i;
 645         unsigned short key;
 646
 647         state->reset_seq_cnt = 0;
 648
 649         for (i = 0; i < sysrq_reset_seq_len; i++) {
 650                 key = sysrq_reset_seq[i];
 651
 652                 if (key == KEY_RESERVED || key > KEY_MAX)
 653                         break;
 654
 655                 __set_bit(key, state->reset_keybit);
 656                 state->reset_seq_len++;
 657
 658                 if (test_bit(key, state->key_down))
 659                         state->reset_seq_cnt++;
 660         }
 661
 662         /* Disable reset until old keys are not released */
 663         state->reset_canceled = state->reset_seq_cnt != 0;
 664
 665         state->reset_seq_version = sysrq_reset_seq_version;
 666 }
 667
 668 static void sysrq_do_reset(struct timer_list *t)
 669 {
 670         struct sysrq_state *state = from_timer(state, t, keyreset_timer);
 671
 672         state->reset_requested = true;
 673
 674         orderly_reboot();
 675 }
 676
 677 static void sysrq_handle_reset_request(struct sysrq_state *state)
 678 {
 679         if (state->reset_requested)
 680                 __handle_sysrq(sysrq_xlate[KEY_B], false);
 681
 682         if (sysrq_reset_downtime_ms)
 683                 mod_timer(&state->keyreset_timer,
 684                         jiffies + msecs_to_jiffies(sysrq_reset_downtime_ms));
 685         else
 686                 sysrq_do_reset(&state->keyreset_timer);
 687 }
 688
 689 static void sysrq_detect_reset_sequence(struct sysrq_state *state,
 690                                         unsigned int code, int value)
 691 {
 692         if (!test_bit(code, state->reset_keybit)) {
 693                 /*
 694                  * Pressing any key _not_ in reset sequence cancels
 695                  * the reset sequence.  Also cancelling the timer in
 696                  * case additional keys were pressed after a reset
 697                  * has been requested.
 698                  */
 699                 if (value && state->reset_seq_cnt) {
 700                         state->reset_canceled = true;
 701                         del_timer(&state->keyreset_timer);
 702                 }
 703         } else if (value == 0) {
 704                 /*
 705                  * Key release - all keys in the reset sequence need
 706                  * to be pressed and held for the reset timeout
 707                  * to hold.
 708                  */
 709                 del_timer(&state->keyreset_timer);
 710
 711                 if (--state->reset_seq_cnt == 0)
 712                         state->reset_canceled = false;
 713         } else if (value == 1) {
 714                 /* key press, not autorepeat */
 715                 if (++state->reset_seq_cnt == state->reset_seq_len &&
 716                     !state->reset_canceled) {
 717                         sysrq_handle_reset_request(state);
 718                 }
 719         }
 720 }
 721
 722 #ifdef CONFIG_OF
 723 static void sysrq_of_get_keyreset_config(void)
 724 {
 725         u32 key;
 726         struct device_node *np;
 727         struct property *prop;
 728         const __be32 *p;
 729
 730         np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
 731         if (!np) {
 732                 pr_debug("No sysrq node found");
 733                 return;
 734         }
 735
 736         /* Reset in case a __weak definition was present */
 737         sysrq_reset_seq_len = 0;
 738
 739         of_property_for_each_u32(np, "keyset", prop, p, key) {
 740                 if (key == KEY_RESERVED || key > KEY_MAX ||
 741                     sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
 742                         break;
 743
 744                 sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
 745         }
 746
 747         /* Get reset timeout if any. */
 748         of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
 749
 750         of_node_put(np);
 751 }
 752 #else
 753 static void sysrq_of_get_keyreset_config(void)
 754 {
 755 }
 756 #endif
 757
 758 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
 759 {
 760         struct sysrq_state *sysrq =
 761                         container_of(work, struct sysrq_state, reinject_work);
 762         struct input_handle *handle = &sysrq->handle;
 763         unsigned int alt_code = sysrq->alt_use;
 764
 765         if (sysrq->need_reinject) {
 766                 /* we do not want the assignment to be reordered */
 767                 sysrq->reinjecting = true;
 768                 mb();
 769
 770                 /* Simulate press and release of Alt + SysRq */
 771                 input_inject_event(handle, EV_KEY, alt_code, 1);
 772                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
 773                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
 774
 775                 input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
 776                 input_inject_event(handle, EV_KEY, alt_code, 0);
 777                 input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
 778
 779                 mb();
 780                 sysrq->reinjecting = false;
 781         }
 782 }
 783
 784 static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
 785                                   unsigned int code, int value)
 786 {
 787         bool was_active = sysrq->active;
 788         bool suppress;
 789
 790         switch (code) {
 791
 792         case KEY_LEFTALT:
 793         case KEY_RIGHTALT:
 794                 if (!value) {
 795                         /* One of ALTs is being released */
 796                         if (sysrq->active && code == sysrq->alt_use)
 797                                 sysrq->active = false;
 798
 799                         sysrq->alt = KEY_RESERVED;
 800
 801                 } else if (value != 2) {
 802                         sysrq->alt = code;
 803                         sysrq->need_reinject = false;
 804                 }
 805                 break;
 806
 807         case KEY_SYSRQ:
 808                 if (value == 1 && sysrq->alt != KEY_RESERVED) {
 809                         sysrq->active = true;
 810                         sysrq->alt_use = sysrq->alt;
 811                         /*
 812                          * If nothing else will be pressed we'll need
 813                          * to re-inject Alt-SysRq keysroke.
 814                          */
 815                         sysrq->need_reinject = true;
 816                 }
 817
 818                 /*
 819                  * Pretend that sysrq was never pressed at all. This
 820                  * is needed to properly handle KGDB which will try
 821                  * to release all keys after exiting debugger. If we
 822                  * do not clear key bit it KGDB will end up sending
 823                  * release events for Alt and SysRq, potentially
 824                  * triggering print screen function.
 825                  */
 826                 if (sysrq->active)
 827                         clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
 828
 829                 break;
 830
 831         default:
 832                 if (sysrq->active && value && value != 2) {
 833                         sysrq->need_reinject = false;
 834                         __handle_sysrq(sysrq_xlate[code], true);
 835                 }
 836                 break;
 837         }
 838
 839         suppress = sysrq->active;
 840
 841         if (!sysrq->active) {
 842
 843                 /*
 844                  * See if reset sequence has changed since the last time.
 845                  */
 846                 if (sysrq->reset_seq_version != sysrq_reset_seq_version)
 847                         sysrq_parse_reset_sequence(sysrq);
 848
 849                 /*
 850                  * If we are not suppressing key presses keep track of
 851                  * keyboard state so we can release keys that have been
 852                  * pressed before entering SysRq mode.
 853                  */
 854                 if (value)
 855                         set_bit(code, sysrq->key_down);
 856                 else
 857                         clear_bit(code, sysrq->key_down);
 858
 859                 if (was_active)
 860                         schedule_work(&sysrq->reinject_work);
 861
 862                 /* Check for reset sequence */
 863                 sysrq_detect_reset_sequence(sysrq, code, value);
 864
 865         } else if (value == 0 && test_and_clear_bit(code, sysrq->key_down)) {
 866                 /*
 867                  * Pass on release events for keys that was pressed before
 868                  * entering SysRq mode.
 869                  */
 870                 suppress = false;
 871         }
 872
 873         return suppress;
 874 }
 875
 876 static bool sysrq_filter(struct input_handle *handle,
 877                          unsigned int type, unsigned int code, int value)
 878 {
 879         struct sysrq_state *sysrq = handle->private;
 880         bool suppress;
 881
 882         /*
 883          * Do not filter anything if we are in the process of re-injecting
 884          * Alt+SysRq combination.
 885          */
 886         if (sysrq->reinjecting)
 887                 return false;
 888
 889         switch (type) {
 890
 891         case EV_SYN:
 892                 suppress = false;
 893                 break;
 894
 895         case EV_KEY:
 896                 suppress = sysrq_handle_keypress(sysrq, code, value);
 897                 break;
 898
 899         default:
 900                 suppress = sysrq->active;
 901                 break;
 902         }
 903
 904         return suppress;
 905 }
 906
 907 static int sysrq_connect(struct input_handler *handler,
 908                          struct input_dev *dev,
 909                          const struct input_device_id *id)
 910 {
 911         struct sysrq_state *sysrq;
 912         int error;
 913
 914         sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
 915         if (!sysrq)
 916                 return -ENOMEM;
 917
 918         INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
 919
 920         sysrq->handle.dev = dev;
 921         sysrq->handle.handler = handler;
 922         sysrq->handle.name = "sysrq";
 923         sysrq->handle.private = sysrq;
 924         timer_setup(&sysrq->keyreset_timer, sysrq_do_reset, 0);
 925
 926         error = input_register_handle(&sysrq->handle);
 927         if (error) {
 928                 pr_err("Failed to register input sysrq handler, error %d\n",
 929                         error);
 930                 goto err_free;
 931         }
 932
 933         error = input_open_device(&sysrq->handle);
 934         if (error) {
 935                 pr_err("Failed to open input device, error %d\n", error);
 936                 goto err_unregister;
 937         }
 938
 939         return 0;
 940
 941  err_unregister:
 942         input_unregister_handle(&sysrq->handle);
 943  err_free:
 944         kfree(sysrq);
 945         return error;
 946 }
 947
 948 static void sysrq_disconnect(struct input_handle *handle)
 949 {
 950         struct sysrq_state *sysrq = handle->private;
 951
 952         input_close_device(handle);
 953         cancel_work_sync(&sysrq->reinject_work);
 954         del_timer_sync(&sysrq->keyreset_timer);
 955         input_unregister_handle(handle);
 956         kfree(sysrq);
 957 }
 958
 959 /*
 960  * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
 961  * keyboards have SysRq key predefined and so user may add it to keymap
 962  * later, but we expect all such keyboards to have left alt.
 963  */
 964 static const struct input_device_id sysrq_ids[] = {
 965         {
 966                 .flags = INPUT_DEVICE_ID_MATCH_EVBIT |
 967                                 INPUT_DEVICE_ID_MATCH_KEYBIT,
 968                 .evbit = { [BIT_WORD(EV_KEY)] = BIT_MASK(EV_KEY) },
 969                 .keybit = { [BIT_WORD(KEY_LEFTALT)] = BIT_MASK(KEY_LEFTALT) },
 970         },
 971         { },
 972 };
 973
 974 static struct input_handler sysrq_handler = {
 975         .filter         = sysrq_filter,
 976         .connect        = sysrq_connect,
 977         .disconnect     = sysrq_disconnect,
 978         .name           = "sysrq",
 979         .id_table       = sysrq_ids,
 980 };
 981
 982 static inline void sysrq_register_handler(void)
 983 {
 984         int error;
 985
 986         sysrq_of_get_keyreset_config();
 987
 988         error = input_register_handler(&sysrq_handler);
 989         if (error)
 990                 pr_err("Failed to register input handler, error %d", error);
 991 }
 992
 993 static inline void sysrq_unregister_handler(void)
 994 {
 995         input_unregister_handler(&sysrq_handler);
 996 }
 997
 998 static int sysrq_reset_seq_param_set(const char *buffer,
 999                                      const struct kernel_param *kp)
1000 {
1001         unsigned long val;
1002         int error;
1003
1004         error = kstrtoul(buffer, 0, &val);
1005         if (error < 0)
1006                 return error;
1007
1008         if (val > KEY_MAX)
1009                 return -EINVAL;
1010
1011         *((unsigned short *)kp->arg) = val;
1012         sysrq_reset_seq_version++;
1013
1014         return 0;
1015 }
1016
1017 static const struct kernel_param_ops param_ops_sysrq_reset_seq = {
1018         .get    = param_get_ushort,
1019         .set    = sysrq_reset_seq_param_set,
1020 };
1021
1022 #define param_check_sysrq_reset_seq(name, p)    \
1023         __param_check(name, p, unsigned short)
1024
1025 /*
1026  * not really modular, but the easiest way to keep compat with existing
1027  * bootargs behaviour is to continue using module_param here.
1028  */
1029 module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
1030                          &sysrq_reset_seq_len, 0644);
1031
1032 module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
1033
1034 #else
1035
1036 static inline void sysrq_register_handler(void)
1037 {
1038 }
1039
1040 static inline void sysrq_unregister_handler(void)
1041 {
1042 }
1043
1044 #endif /* CONFIG_INPUT */
1045
1046 int sysrq_toggle_support(int enable_mask)
1047 {
1048         bool was_enabled = sysrq_on();
1049
1050         sysrq_enabled = enable_mask;
1051
1052         if (was_enabled != sysrq_on()) {
1053                 if (sysrq_on())
1054                         sysrq_register_handler();
1055                 else
1056                         sysrq_unregister_handler();
1057         }
1058
1059         return 0;
1060 }
1061
1062 static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
1063                                 struct sysrq_key_op *remove_op_p)
1064 {
1065         int retval;
1066
1067         spin_lock(&sysrq_key_table_lock);
1068         if (__sysrq_get_key_op(key) == remove_op_p) {
1069                 __sysrq_put_key_op(key, insert_op_p);
1070                 retval = 0;
1071         } else {
1072                 retval = -1;
1073         }
1074         spin_unlock(&sysrq_key_table_lock);
1075
1076         /*
1077          * A concurrent __handle_sysrq either got the old op or the new op.
1078          * Wait for it to go away before returning, so the code for an old
1079          * op is not freed (eg. on module unload) while it is in use.
1080          */
1081         synchronize_rcu();
1082
1083         return retval;
1084 }
1085
1086 int register_sysrq_key(int key, struct sysrq_key_op *op_p)
1087 {
1088         return __sysrq_swap_key_ops(key, op_p, NULL);
1089 }
1090 EXPORT_SYMBOL(register_sysrq_key);
1091
1092 int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
1093 {
1094         return __sysrq_swap_key_ops(key, NULL, op_p);
1095 }
1096 EXPORT_SYMBOL(unregister_sysrq_key);
1097
1098 #ifdef CONFIG_PROC_FS
1099 /*
1100  * writing 'C' to /proc/sysrq-trigger is like sysrq-C
1101  */
1102 static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
1103                                    size_t count, loff_t *ppos)
1104 {
1105         if (count) {
1106                 char c;
1107
1108                 if (get_user(c, buf))
1109                         return -EFAULT;
1110                 __handle_sysrq(c, false);
1111         }
1112
1113         return count;
1114 }
1115
1116 static const struct proc_ops sysrq_trigger_proc_ops = {
1117         .proc_write     = write_sysrq_trigger,
1118         .proc_lseek     = noop_llseek,
1119 };
1120
1121 static void sysrq_init_procfs(void)
1122 {
1123         if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
1124                          &sysrq_trigger_proc_ops))
1125                 pr_err("Failed to register proc interface\n");
1126 }
1127
1128 #else
1129
1130 static inline void sysrq_init_procfs(void)
1131 {
1132 }
1133
1134 #endif /* CONFIG_PROC_FS */
1135
1136 static int __init sysrq_init(void)
1137 {
1138         sysrq_init_procfs();
1139
1140         if (sysrq_on())
1141                 sysrq_register_handler();
1142
1143         return 0;
1144 }
1145 device_initcall(sysrq_init);