arch/x86/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) 2009 IBM Corporation
  18  * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
  19  *
  20  * Authors: Alan Stern <stern@rowland.harvard.edu>
  21  *          K.Prasad <prasad@linux.vnet.ibm.com>
  22  *          Frederic Weisbecker <fweisbec@gmail.com>
  23  */
  24
  25 /*
  26  * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
  27  * using the CPU's debug registers.
  28  */
  29
  30 #include <linux/perf_event.h>
  31 #include <linux/hw_breakpoint.h>
  32 #include <linux/irqflags.h>
  33 #include <linux/notifier.h>
  34 #include <linux/kallsyms.h>
  35 #include <linux/kprobes.h>
  36 #include <linux/percpu.h>
  37 #include <linux/kdebug.h>
  38 #include <linux/kernel.h>
  39 #include <linux/export.h>
  40 #include <linux/sched.h>
  41 #include <linux/smp.h>
  42
  43 #include <asm/hw_breakpoint.h>
  44 #include <asm/processor.h>
  45 #include <asm/debugreg.h>
  46 #include <asm/user.h>
  47
  48 /* Per cpu debug control register value */
  49 DEFINE_PER_CPU(unsigned long, cpu_dr7);
  50 EXPORT_PER_CPU_SYMBOL(cpu_dr7);
  51
  52 /* Per cpu debug address registers values */
  53 static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);
  54
  55 /*
  56  * Stores the breakpoints currently in use on each breakpoint address
  57  * register for each cpus
  58  */
  59 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
  60
  61
  62 static inline unsigned long
  63 __encode_dr7(int drnum, unsigned int len, unsigned int type)
  64 {
  65         unsigned long bp_info;
  66
  67         bp_info = (len | type) & 0xf;
  68         bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
  69         bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));
  70
  71         return bp_info;
  72 }
  73
  74 /*
  75  * Encode the length, type, Exact, and Enable bits for a particular breakpoint
  76  * as stored in debug register 7.
  77  */
  78 unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
  79 {
  80         return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
  81 }
  82
  83 /*
  84  * Decode the length and type bits for a particular breakpoint as
  85  * stored in debug register 7.  Return the "enabled" status.
  86  */
  87 int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
  88 {
  89         int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
  90
  91         *len = (bp_info & 0xc) | 0x40;
  92         *type = (bp_info & 0x3) | 0x80;
  93
  94         return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
  95 }
  96
  97 /*
  98  * Install a perf counter breakpoint.
  99  *
 100  * We seek a free debug address register and use it for this
 101  * breakpoint. Eventually we enable it in the debug control register.
 102  *
 103  * Atomic: we hold the counter->ctx->lock and we only handle variables
 104  * and registers local to this cpu.
 105  */
 106 int arch_install_hw_breakpoint(struct perf_event *bp)
 107 {
 108         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 109         unsigned long *dr7;
 110         int i;
 111
 112         for (i = 0; i < HBP_NUM; i++) {
 113                 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
 114
 115                 if (!*slot) {
 116                         *slot = bp;
 117                         break;
 118                 }
 119         }
 120
 121         if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
 122                 return -EBUSY;
 123
 124         set_debugreg(info->address, i);
 125         __this_cpu_write(cpu_debugreg[i], info->address);
 126
 127         dr7 = this_cpu_ptr(&cpu_dr7);
 128         *dr7 |= encode_dr7(i, info->len, info->type);
 129
 130         set_debugreg(*dr7, 7);
 131         if (info->mask)
 132                 set_dr_addr_mask(info->mask, i);
 133
 134         return 0;
 135 }
 136
 137 /*
 138  * Uninstall the breakpoint contained in the given counter.
 139  *
 140  * First we search the debug address register it uses and then we disable
 141  * it.
 142  *
 143  * Atomic: we hold the counter->ctx->lock and we only handle variables
 144  * and registers local to this cpu.
 145  */
 146 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
 147 {
 148         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 149         unsigned long *dr7;
 150         int i;
 151
 152         for (i = 0; i < HBP_NUM; i++) {
 153                 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
 154
 155                 if (*slot == bp) {
 156                         *slot = NULL;
 157                         break;
 158                 }
 159         }
 160
 161         if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
 162                 return;
 163
 164         dr7 = this_cpu_ptr(&cpu_dr7);
 165         *dr7 &= ~__encode_dr7(i, info->len, info->type);
 166
 167         set_debugreg(*dr7, 7);
 168         if (info->mask)
 169                 set_dr_addr_mask(0, i);
 170 }
 171
 172 /*
 173  * Check for virtual address in kernel space.
 174  */
 175 int arch_check_bp_in_kernelspace(struct perf_event *bp)
 176 {
 177         unsigned int len;
 178         unsigned long va;
 179         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 180
 181         va = info->address;
 182         len = bp->attr.bp_len;
 183
 184         /*
 185          * We don't need to worry about va + len - 1 overflowing:
 186          * we already require that va is aligned to a multiple of len.
 187          */
 188         return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
 189 }
 190
 191 int arch_bp_generic_fields(int x86_len, int x86_type,
 192                            int *gen_len, int *gen_type)
 193 {
 194         /* Type */
 195         switch (x86_type) {
 196         case X86_BREAKPOINT_EXECUTE:
 197                 if (x86_len != X86_BREAKPOINT_LEN_X)
 198                         return -EINVAL;
 199
 200                 *gen_type = HW_BREAKPOINT_X;
 201                 *gen_len = sizeof(long);
 202                 return 0;
 203         case X86_BREAKPOINT_WRITE:
 204                 *gen_type = HW_BREAKPOINT_W;
 205                 break;
 206         case X86_BREAKPOINT_RW:
 207                 *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
 208                 break;
 209         default:
 210                 return -EINVAL;
 211         }
 212
 213         /* Len */
 214         switch (x86_len) {
 215         case X86_BREAKPOINT_LEN_1:
 216                 *gen_len = HW_BREAKPOINT_LEN_1;
 217                 break;
 218         case X86_BREAKPOINT_LEN_2:
 219                 *gen_len = HW_BREAKPOINT_LEN_2;
 220                 break;
 221         case X86_BREAKPOINT_LEN_4:
 222                 *gen_len = HW_BREAKPOINT_LEN_4;
 223                 break;
 224 #ifdef CONFIG_X86_64
 225         case X86_BREAKPOINT_LEN_8:
 226                 *gen_len = HW_BREAKPOINT_LEN_8;
 227                 break;
 228 #endif
 229         default:
 230                 return -EINVAL;
 231         }
 232
 233         return 0;
 234 }
 235
 236
 237 static int arch_build_bp_info(struct perf_event *bp)
 238 {
 239         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 240
 241         info->address = bp->attr.bp_addr;
 242
 243         /* Type */
 244         switch (bp->attr.bp_type) {
 245         case HW_BREAKPOINT_W:
 246                 info->type = X86_BREAKPOINT_WRITE;
 247                 break;
 248         case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
 249                 info->type = X86_BREAKPOINT_RW;
 250                 break;
 251         case HW_BREAKPOINT_X:
 252                 /*
 253                  * We don't allow kernel breakpoints in places that are not
 254                  * acceptable for kprobes.  On non-kprobes kernels, we don't
 255                  * allow kernel breakpoints at all.
 256                  */
 257                 if (bp->attr.bp_addr >= TASK_SIZE_MAX) {
 258 #ifdef CONFIG_KPROBES
 259                         if (within_kprobe_blacklist(bp->attr.bp_addr))
 260                                 return -EINVAL;
 261 #else
 262                         return -EINVAL;
 263 #endif
 264                 }
 265
 266                 info->type = X86_BREAKPOINT_EXECUTE;
 267                 /*
 268                  * x86 inst breakpoints need to have a specific undefined len.
 269                  * But we still need to check userspace is not trying to setup
 270                  * an unsupported length, to get a range breakpoint for example.
 271                  */
 272                 if (bp->attr.bp_len == sizeof(long)) {
 273                         info->len = X86_BREAKPOINT_LEN_X;
 274                         return 0;
 275                 }
 276         default:
 277                 return -EINVAL;
 278         }
 279
 280         /* Len */
 281         info->mask = 0;
 282
 283         switch (bp->attr.bp_len) {
 284         case HW_BREAKPOINT_LEN_1:
 285                 info->len = X86_BREAKPOINT_LEN_1;
 286                 break;
 287         case HW_BREAKPOINT_LEN_2:
 288                 info->len = X86_BREAKPOINT_LEN_2;
 289                 break;
 290         case HW_BREAKPOINT_LEN_4:
 291                 info->len = X86_BREAKPOINT_LEN_4;
 292                 break;
 293 #ifdef CONFIG_X86_64
 294         case HW_BREAKPOINT_LEN_8:
 295                 info->len = X86_BREAKPOINT_LEN_8;
 296                 break;
 297 #endif
 298         default:
 299                 /* AMD range breakpoint */
 300                 if (!is_power_of_2(bp->attr.bp_len))
 301                         return -EINVAL;
 302                 if (bp->attr.bp_addr & (bp->attr.bp_len - 1))
 303                         return -EINVAL;
 304
 305                 if (!boot_cpu_has(X86_FEATURE_BPEXT))
 306                         return -EOPNOTSUPP;
 307
 308                 /*
 309                  * It's impossible to use a range breakpoint to fake out
 310                  * user vs kernel detection because bp_len - 1 can't
 311                  * have the high bit set.  If we ever allow range instruction
 312                  * breakpoints, then we'll have to check for kprobe-blacklisted
 313                  * addresses anywhere in the range.
 314                  */
 315                 info->mask = bp->attr.bp_len - 1;
 316                 info->len = X86_BREAKPOINT_LEN_1;
 317         }
 318
 319         return 0;
 320 }
 321
 322 /*
 323  * Validate the arch-specific HW Breakpoint register settings
 324  */
 325 int arch_validate_hwbkpt_settings(struct perf_event *bp)
 326 {
 327         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 328         unsigned int align;
 329         int ret;
 330
 331
 332         ret = arch_build_bp_info(bp);
 333         if (ret)
 334                 return ret;
 335
 336         switch (info->len) {
 337         case X86_BREAKPOINT_LEN_1:
 338                 align = 0;
 339                 if (info->mask)
 340                         align = info->mask;
 341                 break;
 342         case X86_BREAKPOINT_LEN_2:
 343                 align = 1;
 344                 break;
 345         case X86_BREAKPOINT_LEN_4:
 346                 align = 3;
 347                 break;
 348 #ifdef CONFIG_X86_64
 349         case X86_BREAKPOINT_LEN_8:
 350                 align = 7;
 351                 break;
 352 #endif
 353         default:
 354                 WARN_ON_ONCE(1);
 355                 return -EINVAL;
 356         }
 357
 358         /*
 359          * Check that the low-order bits of the address are appropriate
 360          * for the alignment implied by len.
 361          */
 362         if (info->address & align)
 363                 return -EINVAL;
 364
 365         return 0;
 366 }
 367
 368 /*
 369  * Dump the debug register contents to the user.
 370  * We can't dump our per cpu values because it
 371  * may contain cpu wide breakpoint, something that
 372  * doesn't belong to the current task.
 373  *
 374  * TODO: include non-ptrace user breakpoints (perf)
 375  */
 376 void aout_dump_debugregs(struct user *dump)
 377 {
 378         int i;
 379         int dr7 = 0;
 380         struct perf_event *bp;
 381         struct arch_hw_breakpoint *info;
 382         struct thread_struct *thread = &current->thread;
 383
 384         for (i = 0; i < HBP_NUM; i++) {
 385                 bp = thread->ptrace_bps[i];
 386
 387                 if (bp && !bp->attr.disabled) {
 388                         dump->u_debugreg[i] = bp->attr.bp_addr;
 389                         info = counter_arch_bp(bp);
 390                         dr7 |= encode_dr7(i, info->len, info->type);
 391                 } else {
 392                         dump->u_debugreg[i] = 0;
 393                 }
 394         }
 395
 396         dump->u_debugreg[4] = 0;
 397         dump->u_debugreg[5] = 0;
 398         dump->u_debugreg[6] = current->thread.debugreg6;
 399
 400         dump->u_debugreg[7] = dr7;
 401 }
 402 EXPORT_SYMBOL_GPL(aout_dump_debugregs);
 403
 404 /*
 405  * Release the user breakpoints used by ptrace
 406  */
 407 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 408 {
 409         int i;
 410         struct thread_struct *t = &tsk->thread;
 411
 412         for (i = 0; i < HBP_NUM; i++) {
 413                 unregister_hw_breakpoint(t->ptrace_bps[i]);
 414                 t->ptrace_bps[i] = NULL;
 415         }
 416
 417         t->debugreg6 = 0;
 418         t->ptrace_dr7 = 0;
 419 }
 420
 421 void hw_breakpoint_restore(void)
 422 {
 423         set_debugreg(__this_cpu_read(cpu_debugreg[0]), 0);
 424         set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1);
 425         set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2);
 426         set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3);
 427         set_debugreg(current->thread.debugreg6, 6);
 428         set_debugreg(__this_cpu_read(cpu_dr7), 7);
 429 }
 430 EXPORT_SYMBOL_GPL(hw_breakpoint_restore);
 431
 432 /*
 433  * Handle debug exception notifications.
 434  *
 435  * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
 436  *
 437  * NOTIFY_DONE returned if one of the following conditions is true.
 438  * i) When the causative address is from user-space and the exception
 439  * is a valid one, i.e. not triggered as a result of lazy debug register
 440  * switching
 441  * ii) When there are more bits than trap<n> set in DR6 register (such
 442  * as BD, BS or BT) indicating that more than one debug condition is
 443  * met and requires some more action in do_debug().
 444  *
 445  * NOTIFY_STOP returned for all other cases
 446  *
 447  */
 448 static int hw_breakpoint_handler(struct die_args *args)
 449 {
 450         int i, cpu, rc = NOTIFY_STOP;
 451         struct perf_event *bp;
 452         unsigned long dr7, dr6;
 453         unsigned long *dr6_p;
 454
 455         /* The DR6 value is pointed by args->err */
 456         dr6_p = (unsigned long *)ERR_PTR(args->err);
 457         dr6 = *dr6_p;
 458
 459         /* If it's a single step, TRAP bits are random */
 460         if (dr6 & DR_STEP)
 461                 return NOTIFY_DONE;
 462
 463         /* Do an early return if no trap bits are set in DR6 */
 464         if ((dr6 & DR_TRAP_BITS) == 0)
 465                 return NOTIFY_DONE;
 466
 467         get_debugreg(dr7, 7);
 468         /* Disable breakpoints during exception handling */
 469         set_debugreg(0UL, 7);
 470         /*
 471          * Assert that local interrupts are disabled
 472          * Reset the DRn bits in the virtualized register value.
 473          * The ptrace trigger routine will add in whatever is needed.
 474          */
 475         current->thread.debugreg6 &= ~DR_TRAP_BITS;
 476         cpu = get_cpu();
 477
 478         /* Handle all the breakpoints that were triggered */
 479         for (i = 0; i < HBP_NUM; ++i) {
 480                 if (likely(!(dr6 & (DR_TRAP0 << i))))
 481                         continue;
 482
 483                 /*
 484                  * The counter may be concurrently released but that can only
 485                  * occur from a call_rcu() path. We can then safely fetch
 486                  * the breakpoint, use its callback, touch its counter
 487                  * while we are in an rcu_read_lock() path.
 488                  */
 489                 rcu_read_lock();
 490
 491                 bp = per_cpu(bp_per_reg[i], cpu);
 492                 /*
 493                  * Reset the 'i'th TRAP bit in dr6 to denote completion of
 494                  * exception handling
 495                  */
 496                 (*dr6_p) &= ~(DR_TRAP0 << i);
 497                 /*
 498                  * bp can be NULL due to lazy debug register switching
 499                  * or due to concurrent perf counter removing.
 500                  */
 501                 if (!bp) {
 502                         rcu_read_unlock();
 503                         break;
 504                 }
 505
 506                 perf_bp_event(bp, args->regs);
 507
 508                 /*
 509                  * Set up resume flag to avoid breakpoint recursion when
 510                  * returning back to origin.
 511                  */
 512                 if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
 513                         args->regs->flags |= X86_EFLAGS_RF;
 514
 515                 rcu_read_unlock();
 516         }
 517         /*
 518          * Further processing in do_debug() is needed for a) user-space
 519          * breakpoints (to generate signals) and b) when the system has
 520          * taken exception due to multiple causes
 521          */
 522         if ((current->thread.debugreg6 & DR_TRAP_BITS) ||
 523             (dr6 & (~DR_TRAP_BITS)))
 524                 rc = NOTIFY_DONE;
 525
 526         set_debugreg(dr7, 7);
 527         put_cpu();
 528
 529         return rc;
 530 }
 531
 532 /*
 533  * Handle debug exception notifications.
 534  */
 535 int hw_breakpoint_exceptions_notify(
 536                 struct notifier_block *unused, unsigned long val, void *data)
 537 {
 538         if (val != DIE_DEBUG)
 539                 return NOTIFY_DONE;
 540
 541         return hw_breakpoint_handler(data);
 542 }
 543
 544 void hw_breakpoint_pmu_read(struct perf_event *bp)
 545 {
 546         /* TODO */
 547 }