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/cpu.h>
  45 #include <linux/smp.h>
  46
  47 #include <linux/hw_breakpoint.h>
  48
  49
  50 /*
  51  * Constraints data
  52  */
  53
  54 /* Number of pinned cpu breakpoints in a cpu */
  55 static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned[TYPE_MAX]);
  56
  57 /* Number of pinned task breakpoints in a cpu */
  58 static DEFINE_PER_CPU(unsigned int *, nr_task_bp_pinned[TYPE_MAX]);
  59
  60 /* Number of non-pinned cpu/task breakpoints in a cpu */
  61 static DEFINE_PER_CPU(unsigned int, nr_bp_flexible[TYPE_MAX]);
  62
  63 static int nr_slots[TYPE_MAX];
  64
  65 static int constraints_initialized;
  66
  67 /* Gather the number of total pinned and un-pinned bp in a cpuset */
  68 struct bp_busy_slots {
  69         unsigned int pinned;
  70         unsigned int flexible;
  71 };
  72
  73 /* Serialize accesses to the above constraints */
  74 static DEFINE_MUTEX(nr_bp_mutex);
  75
  76 __weak int hw_breakpoint_weight(struct perf_event *bp)
  77 {
  78         return 1;
  79 }
  80
  81 static inline enum bp_type_idx find_slot_idx(struct perf_event *bp)
  82 {
  83         if (bp->attr.bp_type & HW_BREAKPOINT_RW)
  84                 return TYPE_DATA;
  85
  86         return TYPE_INST;
  87 }
  88
  89 /*
  90  * Report the maximum number of pinned breakpoints a task
  91  * have in this cpu
  92  */
  93 static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
  94 {
  95         int i;
  96         unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
  97
  98         for (i = nr_slots[type] - 1; i >= 0; i--) {
  99                 if (tsk_pinned[i] > 0)
 100                         return i + 1;
 101         }
 102
 103         return 0;
 104 }
 105
 106 static int task_bp_pinned(struct task_struct *tsk, enum bp_type_idx type)
 107 {
 108         struct perf_event_context *ctx = tsk->perf_event_ctxp;
 109         struct list_head *list;
 110         struct perf_event *bp;
 111         unsigned long flags;
 112         int count = 0;
 113
 114         if (WARN_ONCE(!ctx, "No perf context for this task"))
 115                 return 0;
 116
 117         list = &ctx->event_list;
 118
 119         raw_spin_lock_irqsave(&ctx->lock, flags);
 120
 121         /*
 122          * The current breakpoint counter is not included in the list
 123          * at the open() callback time
 124          */
 125         list_for_each_entry(bp, list, event_entry) {
 126                 if (bp->attr.type == PERF_TYPE_BREAKPOINT)
 127                         if (find_slot_idx(bp) == type)
 128                                 count += hw_breakpoint_weight(bp);
 129         }
 130
 131         raw_spin_unlock_irqrestore(&ctx->lock, flags);
 132
 133         return count;
 134 }
 135
 136 /*
 137  * Report the number of pinned/un-pinned breakpoints we have in
 138  * a given cpu (cpu > -1) or in all of them (cpu = -1).
 139  */
 140 static void
 141 fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
 142                     enum bp_type_idx type)
 143 {
 144         int cpu = bp->cpu;
 145         struct task_struct *tsk = bp->ctx->task;
 146
 147         if (cpu >= 0) {
 148                 slots->pinned = per_cpu(nr_cpu_bp_pinned[type], cpu);
 149                 if (!tsk)
 150                         slots->pinned += max_task_bp_pinned(cpu, type);
 151                 else
 152                         slots->pinned += task_bp_pinned(tsk, type);
 153                 slots->flexible = per_cpu(nr_bp_flexible[type], cpu);
 154
 155                 return;
 156         }
 157
 158         for_each_online_cpu(cpu) {
 159                 unsigned int nr;
 160
 161                 nr = per_cpu(nr_cpu_bp_pinned[type], cpu);
 162                 if (!tsk)
 163                         nr += max_task_bp_pinned(cpu, type);
 164                 else
 165                         nr += task_bp_pinned(tsk, type);
 166
 167                 if (nr > slots->pinned)
 168                         slots->pinned = nr;
 169
 170                 nr = per_cpu(nr_bp_flexible[type], cpu);
 171
 172                 if (nr > slots->flexible)
 173                         slots->flexible = nr;
 174         }
 175 }
 176
 177 /*
 178  * For now, continue to consider flexible as pinned, until we can
 179  * ensure no flexible event can ever be scheduled before a pinned event
 180  * in a same cpu.
 181  */
 182 static void
 183 fetch_this_slot(struct bp_busy_slots *slots, int weight)
 184 {
 185         slots->pinned += weight;
 186 }
 187
 188 /*
 189  * Add a pinned breakpoint for the given task in our constraint table
 190  */
 191 static void toggle_bp_task_slot(struct task_struct *tsk, int cpu, bool enable,
 192                                 enum bp_type_idx type, int weight)
 193 {
 194         unsigned int *tsk_pinned;
 195         int old_count = 0;
 196         int old_idx = 0;
 197         int idx = 0;
 198
 199         old_count = task_bp_pinned(tsk, type);
 200         old_idx = old_count - 1;
 201         idx = old_idx + weight;
 202
 203         tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
 204         if (enable) {
 205                 tsk_pinned[idx]++;
 206                 if (old_count > 0)
 207                         tsk_pinned[old_idx]--;
 208         } else {
 209                 tsk_pinned[idx]--;
 210                 if (old_count > 0)
 211                         tsk_pinned[old_idx]++;
 212         }
 213 }
 214
 215 /*
 216  * Add/remove the given breakpoint in our constraint table
 217  */
 218 static void
 219 toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
 220                int weight)
 221 {
 222         int cpu = bp->cpu;
 223         struct task_struct *tsk = bp->ctx->task;
 224
 225         /* Pinned counter task profiling */
 226         if (tsk) {
 227                 if (cpu >= 0) {
 228                         toggle_bp_task_slot(tsk, cpu, enable, type, weight);
 229                         return;
 230                 }
 231
 232                 for_each_online_cpu(cpu)
 233                         toggle_bp_task_slot(tsk, cpu, enable, type, weight);
 234                 return;
 235         }
 236
 237         /* Pinned counter cpu profiling */
 238         if (enable)
 239                 per_cpu(nr_cpu_bp_pinned[type], bp->cpu) += weight;
 240         else
 241                 per_cpu(nr_cpu_bp_pinned[type], bp->cpu) -= weight;
 242 }
 243
 244 /*
 245  * Contraints to check before allowing this new breakpoint counter:
 246  *
 247  *  == Non-pinned counter == (Considered as pinned for now)
 248  *
 249  *   - If attached to a single cpu, check:
 250  *
 251  *       (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
 252  *           + max(per_cpu(nr_task_bp_pinned, cpu)))) < HBP_NUM
 253  *
 254  *       -> If there are already non-pinned counters in this cpu, it means
 255  *          there is already a free slot for them.
 256  *          Otherwise, we check that the maximum number of per task
 257  *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 258  *          (for this cpu) doesn't cover every registers.
 259  *
 260  *   - If attached to every cpus, check:
 261  *
 262  *       (per_cpu(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
 263  *           + max(per_cpu(nr_task_bp_pinned, *)))) < HBP_NUM
 264  *
 265  *       -> This is roughly the same, except we check the number of per cpu
 266  *          bp for every cpu and we keep the max one. Same for the per tasks
 267  *          breakpoints.
 268  *
 269  *
 270  * == Pinned counter ==
 271  *
 272  *   - If attached to a single cpu, check:
 273  *
 274  *       ((per_cpu(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
 275  *            + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
 276  *
 277  *       -> Same checks as before. But now the nr_bp_flexible, if any, must keep
 278  *          one register at least (or they will never be fed).
 279  *
 280  *   - If attached to every cpus, check:
 281  *
 282  *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
 283  *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
 284  */
 285 static int __reserve_bp_slot(struct perf_event *bp)
 286 {
 287         struct bp_busy_slots slots = {0};
 288         enum bp_type_idx type;
 289         int weight;
 290
 291         /* We couldn't initialize breakpoint constraints on boot */
 292         if (!constraints_initialized)
 293                 return -ENOMEM;
 294
 295         /* Basic checks */
 296         if (bp->attr.bp_type == HW_BREAKPOINT_EMPTY ||
 297             bp->attr.bp_type == HW_BREAKPOINT_INVALID)
 298                 return -EINVAL;
 299
 300         type = find_slot_idx(bp);
 301         weight = hw_breakpoint_weight(bp);
 302
 303         fetch_bp_busy_slots(&slots, bp, type);
 304         fetch_this_slot(&slots, weight);
 305
 306         /* Flexible counters need to keep at least one slot */
 307         if (slots.pinned + (!!slots.flexible) > nr_slots[type])
 308                 return -ENOSPC;
 309
 310         toggle_bp_slot(bp, true, type, weight);
 311
 312         return 0;
 313 }
 314
 315 int reserve_bp_slot(struct perf_event *bp)
 316 {
 317         int ret;
 318
 319         mutex_lock(&nr_bp_mutex);
 320
 321         ret = __reserve_bp_slot(bp);
 322
 323         mutex_unlock(&nr_bp_mutex);
 324
 325         return ret;
 326 }
 327
 328 static void __release_bp_slot(struct perf_event *bp)
 329 {
 330         enum bp_type_idx type;
 331         int weight;
 332
 333         type = find_slot_idx(bp);
 334         weight = hw_breakpoint_weight(bp);
 335         toggle_bp_slot(bp, false, type, weight);
 336 }
 337
 338 void release_bp_slot(struct perf_event *bp)
 339 {
 340         mutex_lock(&nr_bp_mutex);
 341
 342         __release_bp_slot(bp);
 343
 344         mutex_unlock(&nr_bp_mutex);
 345 }
 346
 347 /*
 348  * Allow the kernel debugger to reserve breakpoint slots without
 349  * taking a lock using the dbg_* variant of for the reserve and
 350  * release breakpoint slots.
 351  */
 352 int dbg_reserve_bp_slot(struct perf_event *bp)
 353 {
 354         if (mutex_is_locked(&nr_bp_mutex))
 355                 return -1;
 356
 357         return __reserve_bp_slot(bp);
 358 }
 359
 360 int dbg_release_bp_slot(struct perf_event *bp)
 361 {
 362         if (mutex_is_locked(&nr_bp_mutex))
 363                 return -1;
 364
 365         __release_bp_slot(bp);
 366
 367         return 0;
 368 }
 369
 370 static int validate_hw_breakpoint(struct perf_event *bp)
 371 {
 372         int ret;
 373
 374         ret = arch_validate_hwbkpt_settings(bp);
 375         if (ret)
 376                 return ret;
 377
 378         if (arch_check_bp_in_kernelspace(bp)) {
 379                 if (bp->attr.exclude_kernel)
 380                         return -EINVAL;
 381                 /*
 382                  * Don't let unprivileged users set a breakpoint in the trap
 383                  * path to avoid trap recursion attacks.
 384                  */
 385                 if (!capable(CAP_SYS_ADMIN))
 386                         return -EPERM;
 387         }
 388
 389         return 0;
 390 }
 391
 392 int register_perf_hw_breakpoint(struct perf_event *bp)
 393 {
 394         int ret;
 395
 396         ret = reserve_bp_slot(bp);
 397         if (ret)
 398                 return ret;
 399
 400         ret = validate_hw_breakpoint(bp);
 401
 402         /* if arch_validate_hwbkpt_settings() fails then release bp slot */
 403         if (ret)
 404                 release_bp_slot(bp);
 405
 406         return ret;
 407 }
 408
 409 /**
 410  * register_user_hw_breakpoint - register a hardware breakpoint for user space
 411  * @attr: breakpoint attributes
 412  * @triggered: callback to trigger when we hit the breakpoint
 413  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 414  */
 415 struct perf_event *
 416 register_user_hw_breakpoint(struct perf_event_attr *attr,
 417                             perf_overflow_handler_t triggered,
 418                             struct task_struct *tsk)
 419 {
 420         return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
 421 }
 422 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 423
 424 /**
 425  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 426  * @bp: the breakpoint structure to modify
 427  * @attr: new 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 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 432 {
 433         u64 old_addr = bp->attr.bp_addr;
 434         u64 old_len = bp->attr.bp_len;
 435         int old_type = bp->attr.bp_type;
 436         int err = 0;
 437
 438         perf_event_disable(bp);
 439
 440         bp->attr.bp_addr = attr->bp_addr;
 441         bp->attr.bp_type = attr->bp_type;
 442         bp->attr.bp_len = attr->bp_len;
 443
 444         if (attr->disabled)
 445                 goto end;
 446
 447         err = validate_hw_breakpoint(bp);
 448         if (!err)
 449                 perf_event_enable(bp);
 450
 451         if (err) {
 452                 bp->attr.bp_addr = old_addr;
 453                 bp->attr.bp_type = old_type;
 454                 bp->attr.bp_len = old_len;
 455                 if (!bp->attr.disabled)
 456                         perf_event_enable(bp);
 457
 458                 return err;
 459         }
 460
 461 end:
 462         bp->attr.disabled = attr->disabled;
 463
 464         return 0;
 465 }
 466 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 467
 468 /**
 469  * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 470  * @bp: the breakpoint structure to unregister
 471  */
 472 void unregister_hw_breakpoint(struct perf_event *bp)
 473 {
 474         if (!bp)
 475                 return;
 476         perf_event_release_kernel(bp);
 477 }
 478 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 479
 480 /**
 481  * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 482  * @attr: breakpoint attributes
 483  * @triggered: callback to trigger when we hit the breakpoint
 484  *
 485  * @return a set of per_cpu pointers to perf events
 486  */
 487 struct perf_event * __percpu *
 488 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 489                             perf_overflow_handler_t triggered)
 490 {
 491         struct perf_event * __percpu *cpu_events, **pevent, *bp;
 492         long err;
 493         int cpu;
 494
 495         cpu_events = alloc_percpu(typeof(*cpu_events));
 496         if (!cpu_events)
 497                 return (void __percpu __force *)ERR_PTR(-ENOMEM);
 498
 499         get_online_cpus();
 500         for_each_online_cpu(cpu) {
 501                 pevent = per_cpu_ptr(cpu_events, cpu);
 502                 bp = perf_event_create_kernel_counter(attr, cpu, -1, triggered);
 503
 504                 *pevent = bp;
 505
 506                 if (IS_ERR(bp)) {
 507                         err = PTR_ERR(bp);
 508                         goto fail;
 509                 }
 510         }
 511         put_online_cpus();
 512
 513         return cpu_events;
 514
 515 fail:
 516         for_each_online_cpu(cpu) {
 517                 pevent = per_cpu_ptr(cpu_events, cpu);
 518                 if (IS_ERR(*pevent))
 519                         break;
 520                 unregister_hw_breakpoint(*pevent);
 521         }
 522         put_online_cpus();
 523
 524         free_percpu(cpu_events);
 525         return (void __percpu __force *)ERR_PTR(err);
 526 }
 527 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 528
 529 /**
 530  * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 531  * @cpu_events: the per cpu set of events to unregister
 532  */
 533 void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 534 {
 535         int cpu;
 536         struct perf_event **pevent;
 537
 538         for_each_possible_cpu(cpu) {
 539                 pevent = per_cpu_ptr(cpu_events, cpu);
 540                 unregister_hw_breakpoint(*pevent);
 541         }
 542         free_percpu(cpu_events);
 543 }
 544 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 545
 546 static struct notifier_block hw_breakpoint_exceptions_nb = {
 547         .notifier_call = hw_breakpoint_exceptions_notify,
 548         /* we need to be notified first */
 549         .priority = 0x7fffffff
 550 };
 551
 552 static int __init init_hw_breakpoint(void)
 553 {
 554         unsigned int **task_bp_pinned;
 555         int cpu, err_cpu;
 556         int i;
 557
 558         for (i = 0; i < TYPE_MAX; i++)
 559                 nr_slots[i] = hw_breakpoint_slots(i);
 560
 561         for_each_possible_cpu(cpu) {
 562                 for (i = 0; i < TYPE_MAX; i++) {
 563                         task_bp_pinned = &per_cpu(nr_task_bp_pinned[i], cpu);
 564                         *task_bp_pinned = kzalloc(sizeof(int) * nr_slots[i],
 565                                                   GFP_KERNEL);
 566                         if (!*task_bp_pinned)
 567                                 goto err_alloc;
 568                 }
 569         }
 570
 571         constraints_initialized = 1;
 572
 573         return register_die_notifier(&hw_breakpoint_exceptions_nb);
 574
 575  err_alloc:
 576         for_each_possible_cpu(err_cpu) {
 577                 if (err_cpu == cpu)
 578                         break;
 579                 for (i = 0; i < TYPE_MAX; i++)
 580                         kfree(per_cpu(nr_task_bp_pinned[i], cpu));
 581         }
 582
 583         return -ENOMEM;
 584 }
 585 core_initcall(init_hw_breakpoint);
 586
 587
 588 struct pmu perf_ops_bp = {
 589         .enable         = arch_install_hw_breakpoint,
 590         .disable        = arch_uninstall_hw_breakpoint,
 591         .read           = hw_breakpoint_pmu_read,
 592 };