kernel/hw_breakpoint.c

   1 /*
   2  * This program is free software; you can redistribute it and/or modify
   3  * it under the terms of the GNU General Public License as published by
   4  * the Free Software Foundation; either version 2 of the License, or
   5  * (at your option) any later version.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  *
  12  * You should have received a copy of the GNU General Public License
  13  * along with this program; if not, write to the Free Software
  14  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  15  *
  16  * Copyright (C) 2007 Alan Stern
  17  * Copyright (C) IBM Corporation, 2009
  18  * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
  19  *
  20  * Thanks to Ingo Molnar for his many suggestions.
  21  *
  22  * Authors: Alan Stern <stern@rowland.harvard.edu>
  23  *          K.Prasad <prasad@linux.vnet.ibm.com>
  24  *          Frederic Weisbecker <fweisbec@gmail.com>
  25  */
  26
  27 /*
  28  * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
  29  * using the CPU's debug registers.
  30  * This file contains the arch-independent routines.
  31  */
  32
  33 #include <linux/irqflags.h>
  34 #include <linux/kallsyms.h>
  35 #include <linux/notifier.h>
  36 #include <linux/kprobes.h>
  37 #include <linux/kdebug.h>
  38 #include <linux/kernel.h>
  39 #include <linux/module.h>
  40 #include <linux/percpu.h>
  41 #include <linux/sched.h>
  42 #include <linux/init.h>
  43 #include <linux/slab.h>
  44 #include <linux/list.h>
  45 #include <linux/cpu.h>
  46 #include <linux/smp.h>
  47
  48 #include <linux/hw_breakpoint.h>
  49
  50
  51 /*
  52  * Constraints data
  53  */
  54
  55 /* Number of pinned cpu breakpoints in a cpu */
  56 static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned[TYPE_MAX]);
  57
  58 /* Number of pinned task breakpoints in a cpu */
  59 static DEFINE_PER_CPU(unsigned int *, nr_task_bp_pinned[TYPE_MAX]);
  60
  61 /* Number of non-pinned cpu/task breakpoints in a cpu */
  62 static DEFINE_PER_CPU(unsigned int, nr_bp_flexible[TYPE_MAX]);
  63
  64 static int nr_slots[TYPE_MAX];
  65
  66 /* Keep track of the breakpoints attached to tasks */
  67 static LIST_HEAD(bp_task_head);
  68
  69 static int constraints_initialized;
  70
  71 /* Gather the number of total pinned and un-pinned bp in a cpuset */
  72 struct bp_busy_slots {
  73         unsigned int pinned;
  74         unsigned int flexible;
  75 };
  76
  77 /* Serialize accesses to the above constraints */
  78 static DEFINE_MUTEX(nr_bp_mutex);
  79
  80 __weak int hw_breakpoint_weight(struct perf_event *bp)
  81 {
  82         return 1;
  83 }
  84
  85 static inline enum bp_type_idx find_slot_idx(struct perf_event *bp)
  86 {
  87         if (bp->attr.bp_type & HW_BREAKPOINT_RW)
  88                 return TYPE_DATA;
  89
  90         return TYPE_INST;
  91 }
  92
  93 /*
  94  * Report the maximum number of pinned breakpoints a task
  95  * have in this cpu
  96  */
  97 static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
  98 {
  99         int i;
 100         unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
 101
 102         for (i = nr_slots[type] - 1; i >= 0; i--) {
 103                 if (tsk_pinned[i] > 0)
 104                         return i + 1;
 105         }
 106
 107         return 0;
 108 }
 109
 110 /*
 111  * Count the number of breakpoints of the same type and same task.
 112  * The given event must be not on the list.
 113  */
 114 static int task_bp_pinned(struct perf_event *bp, enum bp_type_idx type)
 115 {
 116         struct perf_event_context *ctx = bp->ctx;
 117         struct perf_event *iter;
 118         int count = 0;
 119
 120         list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
 121                 if (iter->ctx == ctx && find_slot_idx(iter) == type)
 122                         count += hw_breakpoint_weight(iter);
 123         }
 124
 125         return count;
 126 }
 127
 128 /*
 129  * Report the number of pinned/un-pinned breakpoints we have in
 130  * a given cpu (cpu > -1) or in all of them (cpu = -1).
 131  */
 132 static void
 133 fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
 134                     enum bp_type_idx type)
 135 {
 136         int cpu = bp->cpu;
 137         struct task_struct *tsk = bp->ctx->task;
 138
 139         if (cpu >= 0) {
 140                 slots->pinned = per_cpu(nr_cpu_bp_pinned[type], cpu);
 141                 if (!tsk)
 142                         slots->pinned += max_task_bp_pinned(cpu, type);
 143                 else
 144                         slots->pinned += task_bp_pinned(bp, type);
 145                 slots->flexible = per_cpu(nr_bp_flexible[type], cpu);
 146
 147                 return;
 148         }
 149
 150         for_each_online_cpu(cpu) {
 151                 unsigned int nr;
 152
 153                 nr = per_cpu(nr_cpu_bp_pinned[type], cpu);
 154                 if (!tsk)
 155                         nr += max_task_bp_pinned(cpu, type);
 156                 else
 157                         nr += task_bp_pinned(bp, type);
 158
 159                 if (nr > slots->pinned)
 160                         slots->pinned = nr;
 161
 162                 nr = per_cpu(nr_bp_flexible[type], cpu);
 163
 164                 if (nr > slots->flexible)
 165                         slots->flexible = nr;
 166         }
 167 }
 168
 169 /*
 170  * For now, continue to consider flexible as pinned, until we can
 171  * ensure no flexible event can ever be scheduled before a pinned event
 172  * in a same cpu.
 173  */
 174 static void
 175 fetch_this_slot(struct bp_busy_slots *slots, int weight)
 176 {
 177         slots->pinned += weight;
 178 }
 179
 180 /*
 181  * Add a pinned breakpoint for the given task in our constraint table
 182  */
 183 static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
 184                                 enum bp_type_idx type, int weight)
 185 {
 186         unsigned int *tsk_pinned;
 187         int old_count = 0;
 188         int old_idx = 0;
 189         int idx = 0;
 190
 191         old_count = task_bp_pinned(bp, type);
 192         old_idx = old_count - 1;
 193         idx = old_idx + weight;
 194
 195         /* tsk_pinned[n] is the number of tasks having n breakpoints */
 196         tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
 197         if (enable) {
 198                 tsk_pinned[idx]++;
 199                 if (old_count > 0)
 200                         tsk_pinned[old_idx]--;
 201         } else {
 202                 tsk_pinned[idx]--;
 203                 if (old_count > 0)
 204                         tsk_pinned[old_idx]++;
 205         }
 206 }
 207
 208 /*
 209  * Add/remove the given breakpoint in our constraint table
 210  */
 211 static void
 212 toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
 213                int weight)
 214 {
 215         int cpu = bp->cpu;
 216         struct task_struct *tsk = bp->ctx->task;
 217
 218         /* Pinned counter cpu profiling */
 219         if (!tsk) {
 220
 221                 if (enable)
 222                         per_cpu(nr_cpu_bp_pinned[type], bp->cpu) += weight;
 223                 else
 224                         per_cpu(nr_cpu_bp_pinned[type], bp->cpu) -= weight;
 225                 return;
 226         }
 227
 228         /* Pinned counter task profiling */
 229
 230         if (!enable)
 231                 list_del(&bp->hw.bp_list);
 232
 233         if (cpu >= 0) {
 234                 toggle_bp_task_slot(bp, cpu, enable, type, weight);
 235         } else {
 236                 for_each_online_cpu(cpu)
 237                         toggle_bp_task_slot(bp, cpu, enable, type, weight);
 238         }
 239
 240         if (enable)
 241                 list_add_tail(&bp->hw.bp_list, &bp_task_head);
 242 }
 243
 244 /*
 245  * Function to perform processor-specific cleanup during unregistration
 246  */
 247 __weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
 248 {
 249         /*
 250          * A weak stub function here for those archs that don't define
 251          * it inside arch/.../kernel/hw_breakpoint.c
 252          */
 253 }
 254
 255 /*
 256  * Contraints to check before allowing this new breakpoint counter:
 257  *
 258  *  == Non-pinned counter == (Considered as pinned for now)
 259  *
 260  *   - If attached to a single cpu, check:
 261  *
 262  *       (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
 263  *           + max(per_cpu(nr_task_bp_pinned, cpu)))) < HBP_NUM
 264  *
 265  *       -> If there are already non-pinned counters in this cpu, it means
 266  *          there is already a free slot for them.
 267  *          Otherwise, we check that the maximum number of per task
 268  *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 269  *          (for this cpu) doesn't cover every registers.
 270  *
 271  *   - If attached to every cpus, check:
 272  *
 273  *       (per_cpu(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
 274  *           + max(per_cpu(nr_task_bp_pinned, *)))) < HBP_NUM
 275  *
 276  *       -> This is roughly the same, except we check the number of per cpu
 277  *          bp for every cpu and we keep the max one. Same for the per tasks
 278  *          breakpoints.
 279  *
 280  *
 281  * == Pinned counter ==
 282  *
 283  *   - If attached to a single cpu, check:
 284  *
 285  *       ((per_cpu(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
 286  *            + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
 287  *
 288  *       -> Same checks as before. But now the nr_bp_flexible, if any, must keep
 289  *          one register at least (or they will never be fed).
 290  *
 291  *   - If attached to every cpus, check:
 292  *
 293  *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
 294  *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
 295  */
 296 static int __reserve_bp_slot(struct perf_event *bp)
 297 {
 298         struct bp_busy_slots slots = {0};
 299         enum bp_type_idx type;
 300         int weight;
 301
 302         /* We couldn't initialize breakpoint constraints on boot */
 303         if (!constraints_initialized)
 304                 return -ENOMEM;
 305
 306         /* Basic checks */
 307         if (bp->attr.bp_type == HW_BREAKPOINT_EMPTY ||
 308             bp->attr.bp_type == HW_BREAKPOINT_INVALID)
 309                 return -EINVAL;
 310
 311         type = find_slot_idx(bp);
 312         weight = hw_breakpoint_weight(bp);
 313
 314         fetch_bp_busy_slots(&slots, bp, type);
 315         /*
 316          * Simulate the addition of this breakpoint to the constraints
 317          * and see the result.
 318          */
 319         fetch_this_slot(&slots, weight);
 320
 321         /* Flexible counters need to keep at least one slot */
 322         if (slots.pinned + (!!slots.flexible) > nr_slots[type])
 323                 return -ENOSPC;
 324
 325         toggle_bp_slot(bp, true, type, weight);
 326
 327         return 0;
 328 }
 329
 330 int reserve_bp_slot(struct perf_event *bp)
 331 {
 332         int ret;
 333
 334         mutex_lock(&nr_bp_mutex);
 335
 336         ret = __reserve_bp_slot(bp);
 337
 338         mutex_unlock(&nr_bp_mutex);
 339
 340         return ret;
 341 }
 342
 343 static void __release_bp_slot(struct perf_event *bp)
 344 {
 345         enum bp_type_idx type;
 346         int weight;
 347
 348         type = find_slot_idx(bp);
 349         weight = hw_breakpoint_weight(bp);
 350         toggle_bp_slot(bp, false, type, weight);
 351 }
 352
 353 void release_bp_slot(struct perf_event *bp)
 354 {
 355         mutex_lock(&nr_bp_mutex);
 356
 357         arch_unregister_hw_breakpoint(bp);
 358         __release_bp_slot(bp);
 359
 360         mutex_unlock(&nr_bp_mutex);
 361 }
 362
 363 /*
 364  * Allow the kernel debugger to reserve breakpoint slots without
 365  * taking a lock using the dbg_* variant of for the reserve and
 366  * release breakpoint slots.
 367  */
 368 int dbg_reserve_bp_slot(struct perf_event *bp)
 369 {
 370         if (mutex_is_locked(&nr_bp_mutex))
 371                 return -1;
 372
 373         return __reserve_bp_slot(bp);
 374 }
 375
 376 int dbg_release_bp_slot(struct perf_event *bp)
 377 {
 378         if (mutex_is_locked(&nr_bp_mutex))
 379                 return -1;
 380
 381         __release_bp_slot(bp);
 382
 383         return 0;
 384 }
 385
 386 static int validate_hw_breakpoint(struct perf_event *bp)
 387 {
 388         int ret;
 389
 390         ret = arch_validate_hwbkpt_settings(bp);
 391         if (ret)
 392                 return ret;
 393
 394         if (arch_check_bp_in_kernelspace(bp)) {
 395                 if (bp->attr.exclude_kernel)
 396                         return -EINVAL;
 397                 /*
 398                  * Don't let unprivileged users set a breakpoint in the trap
 399                  * path to avoid trap recursion attacks.
 400                  */
 401                 if (!capable(CAP_SYS_ADMIN))
 402                         return -EPERM;
 403         }
 404
 405         return 0;
 406 }
 407
 408 int register_perf_hw_breakpoint(struct perf_event *bp)
 409 {
 410         int ret;
 411
 412         ret = reserve_bp_slot(bp);
 413         if (ret)
 414                 return ret;
 415
 416         ret = validate_hw_breakpoint(bp);
 417
 418         /* if arch_validate_hwbkpt_settings() fails then release bp slot */
 419         if (ret)
 420                 release_bp_slot(bp);
 421
 422         return ret;
 423 }
 424
 425 /**
 426  * register_user_hw_breakpoint - register a hardware breakpoint for user space
 427  * @attr: breakpoint attributes
 428  * @triggered: callback to trigger when we hit the breakpoint
 429  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 430  */
 431 struct perf_event *
 432 register_user_hw_breakpoint(struct perf_event_attr *attr,
 433                             perf_overflow_handler_t triggered,
 434                             struct task_struct *tsk)
 435 {
 436         return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
 437 }
 438 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 439
 440 /**
 441  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 442  * @bp: the breakpoint structure to modify
 443  * @attr: new breakpoint attributes
 444  * @triggered: callback to trigger when we hit the breakpoint
 445  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 446  */
 447 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 448 {
 449         u64 old_addr = bp->attr.bp_addr;
 450         u64 old_len = bp->attr.bp_len;
 451         int old_type = bp->attr.bp_type;
 452         int err = 0;
 453
 454         perf_event_disable(bp);
 455
 456         bp->attr.bp_addr = attr->bp_addr;
 457         bp->attr.bp_type = attr->bp_type;
 458         bp->attr.bp_len = attr->bp_len;
 459
 460         if (attr->disabled)
 461                 goto end;
 462
 463         err = validate_hw_breakpoint(bp);
 464         if (!err)
 465                 perf_event_enable(bp);
 466
 467         if (err) {
 468                 bp->attr.bp_addr = old_addr;
 469                 bp->attr.bp_type = old_type;
 470                 bp->attr.bp_len = old_len;
 471                 if (!bp->attr.disabled)
 472                         perf_event_enable(bp);
 473
 474                 return err;
 475         }
 476
 477 end:
 478         bp->attr.disabled = attr->disabled;
 479
 480         return 0;
 481 }
 482 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 483
 484 /**
 485  * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 486  * @bp: the breakpoint structure to unregister
 487  */
 488 void unregister_hw_breakpoint(struct perf_event *bp)
 489 {
 490         if (!bp)
 491                 return;
 492         perf_event_release_kernel(bp);
 493 }
 494 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 495
 496 /**
 497  * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 498  * @attr: breakpoint attributes
 499  * @triggered: callback to trigger when we hit the breakpoint
 500  *
 501  * @return a set of per_cpu pointers to perf events
 502  */
 503 struct perf_event * __percpu *
 504 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 505                             perf_overflow_handler_t triggered)
 506 {
 507         struct perf_event * __percpu *cpu_events, **pevent, *bp;
 508         long err;
 509         int cpu;
 510
 511         cpu_events = alloc_percpu(typeof(*cpu_events));
 512         if (!cpu_events)
 513                 return (void __percpu __force *)ERR_PTR(-ENOMEM);
 514
 515         get_online_cpus();
 516         for_each_online_cpu(cpu) {
 517                 pevent = per_cpu_ptr(cpu_events, cpu);
 518                 bp = perf_event_create_kernel_counter(attr, cpu, -1, triggered);
 519
 520                 *pevent = bp;
 521
 522                 if (IS_ERR(bp)) {
 523                         err = PTR_ERR(bp);
 524                         goto fail;
 525                 }
 526         }
 527         put_online_cpus();
 528
 529         return cpu_events;
 530
 531 fail:
 532         for_each_online_cpu(cpu) {
 533                 pevent = per_cpu_ptr(cpu_events, cpu);
 534                 if (IS_ERR(*pevent))
 535                         break;
 536                 unregister_hw_breakpoint(*pevent);
 537         }
 538         put_online_cpus();
 539
 540         free_percpu(cpu_events);
 541         return (void __percpu __force *)ERR_PTR(err);
 542 }
 543 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 544
 545 /**
 546  * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 547  * @cpu_events: the per cpu set of events to unregister
 548  */
 549 void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 550 {
 551         int cpu;
 552         struct perf_event **pevent;
 553
 554         for_each_possible_cpu(cpu) {
 555                 pevent = per_cpu_ptr(cpu_events, cpu);
 556                 unregister_hw_breakpoint(*pevent);
 557         }
 558         free_percpu(cpu_events);
 559 }
 560 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 561
 562 static struct notifier_block hw_breakpoint_exceptions_nb = {
 563         .notifier_call = hw_breakpoint_exceptions_notify,
 564         /* we need to be notified first */
 565         .priority = 0x7fffffff
 566 };
 567
 568 static void bp_perf_event_destroy(struct perf_event *event)
 569 {
 570         release_bp_slot(event);
 571 }
 572
 573 static int hw_breakpoint_event_init(struct perf_event *bp)
 574 {
 575         int err;
 576
 577         if (bp->attr.type != PERF_TYPE_BREAKPOINT)
 578                 return -ENOENT;
 579
 580         err = register_perf_hw_breakpoint(bp);
 581         if (err)
 582                 return err;
 583
 584         bp->destroy = bp_perf_event_destroy;
 585
 586         return 0;
 587 }
 588
 589 static int hw_breakpoint_add(struct perf_event *bp, int flags)
 590 {
 591         if (!(flags & PERF_EF_START))
 592                 bp->hw.state = PERF_HES_STOPPED;
 593
 594         return arch_install_hw_breakpoint(bp);
 595 }
 596
 597 static void hw_breakpoint_del(struct perf_event *bp, int flags)
 598 {
 599         arch_uninstall_hw_breakpoint(bp);
 600 }
 601
 602 static void hw_breakpoint_start(struct perf_event *bp, int flags)
 603 {
 604         bp->hw.state = 0;
 605 }
 606
 607 static void hw_breakpoint_stop(struct perf_event *bp, int flags)
 608 {
 609         bp->hw.state = PERF_HES_STOPPED;
 610 }
 611
 612 static struct pmu perf_breakpoint = {
 613         .event_init     = hw_breakpoint_event_init,
 614         .add            = hw_breakpoint_add,
 615         .del            = hw_breakpoint_del,
 616         .start          = hw_breakpoint_start,
 617         .stop           = hw_breakpoint_stop,
 618         .read           = hw_breakpoint_pmu_read,
 619 };
 620
 621 static int __init init_hw_breakpoint(void)
 622 {
 623         unsigned int **task_bp_pinned;
 624         int cpu, err_cpu;
 625         int i;
 626
 627         for (i = 0; i < TYPE_MAX; i++)
 628                 nr_slots[i] = hw_breakpoint_slots(i);
 629
 630         for_each_possible_cpu(cpu) {
 631                 for (i = 0; i < TYPE_MAX; i++) {
 632                         task_bp_pinned = &per_cpu(nr_task_bp_pinned[i], cpu);
 633                         *task_bp_pinned = kzalloc(sizeof(int) * nr_slots[i],
 634                                                   GFP_KERNEL);
 635                         if (!*task_bp_pinned)
 636                                 goto err_alloc;
 637                 }
 638         }
 639
 640         constraints_initialized = 1;
 641
 642         perf_pmu_register(&perf_breakpoint);
 643
 644         return register_die_notifier(&hw_breakpoint_exceptions_nb);
 645
 646  err_alloc:
 647         for_each_possible_cpu(err_cpu) {
 648                 if (err_cpu == cpu)
 649                         break;
 650                 for (i = 0; i < TYPE_MAX; i++)
 651                         kfree(per_cpu(nr_task_bp_pinned[i], cpu));
 652         }
 653
 654         return -ENOMEM;
 655 }
 656 core_initcall(init_hw_breakpoint);
 657
 658