nptl/allocatestack.c

   1 /* Copyright (C) 2002-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <signal.h>
  21 #include <stdint.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <sys/mman.h>
  25 #include <sys/param.h>
  26 #include <dl-sysdep.h>
  27 #include <dl-tls.h>
  28 #include <tls.h>
  29 #include <list.h>
  30 #include <lowlevellock.h>
  31 #include <futex-internal.h>
  32 #include <kernel-features.h>
  33 #include <nptl-stack.h>
  34 #include <libc-lock.h>
  35 #include <tls-internal.h>
  36
  37 /* Default alignment of stack.  */
  38 #ifndef STACK_ALIGN
  39 # define STACK_ALIGN __alignof__ (long double)
  40 #endif
  41
  42 /* Default value for minimal stack size after allocating thread
  43    descriptor and guard.  */
  44 #ifndef MINIMAL_REST_STACK
  45 # define MINIMAL_REST_STACK     4096
  46 #endif
  47
  48
  49 /* Newer kernels have the MAP_STACK flag to indicate a mapping is used for
  50    a stack.  Use it when possible.  */
  51 #ifndef MAP_STACK
  52 # define MAP_STACK 0
  53 #endif
  54
  55 /* Get a stack frame from the cache.  We have to match by size since
  56    some blocks might be too small or far too large.  */
  57 static struct pthread *
  58 get_cached_stack (size_t *sizep, void **memp)
  59 {
  60   size_t size = *sizep;
  61   struct pthread *result = NULL;
  62   list_t *entry;
  63
  64   lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
  65
  66   /* Search the cache for a matching entry.  We search for the
  67      smallest stack which has at least the required size.  Note that
  68      in normal situations the size of all allocated stacks is the
  69      same.  As the very least there are only a few different sizes.
  70      Therefore this loop will exit early most of the time with an
  71      exact match.  */
  72   list_for_each (entry, &GL (dl_stack_cache))
  73     {
  74       struct pthread *curr;
  75
  76       curr = list_entry (entry, struct pthread, list);
  77       if (__nptl_stack_in_use (curr) && curr->stackblock_size >= size)
  78         {
  79           if (curr->stackblock_size == size)
  80             {
  81               result = curr;
  82               break;
  83             }
  84
  85           if (result == NULL
  86               || result->stackblock_size > curr->stackblock_size)
  87             result = curr;
  88         }
  89     }
  90
  91   if (__builtin_expect (result == NULL, 0)
  92       /* Make sure the size difference is not too excessive.  In that
  93          case we do not use the block.  */
  94       || __builtin_expect (result->stackblock_size > 4 * size, 0))
  95     {
  96       /* Release the lock.  */
  97       lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
  98
  99       return NULL;
 100     }
 101
 102   /* Don't allow setxid until cloned.  */
 103   result->setxid_futex = -1;
 104
 105   /* Dequeue the entry.  */
 106   __nptl_stack_list_del (&result->list);
 107
 108   /* And add to the list of stacks in use.  */
 109   __nptl_stack_list_add (&result->list, &GL (dl_stack_used));
 110
 111   /* And decrease the cache size.  */
 112   GL (dl_stack_cache_actsize) -= result->stackblock_size;
 113
 114   /* Release the lock early.  */
 115   lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 116
 117   /* Report size and location of the stack to the caller.  */
 118   *sizep = result->stackblock_size;
 119   *memp = result->stackblock;
 120
 121   /* Cancellation handling is back to the default.  */
 122   result->cancelhandling = 0;
 123   result->cleanup = NULL;
 124   result->setup_failed = 0;
 125
 126   /* No pending event.  */
 127   result->nextevent = NULL;
 128
 129   result->exiting = false;
 130   __libc_lock_init (result->exit_lock);
 131   memset (&result->tls_state, 0, sizeof result->tls_state);
 132
 133   /* Clear the DTV.  */
 134   dtv_t *dtv = GET_DTV (TLS_TPADJ (result));
 135   for (size_t cnt = 0; cnt < dtv[-1].counter; ++cnt)
 136     free (dtv[1 + cnt].pointer.to_free);
 137   memset (dtv, '\0', (dtv[-1].counter + 1) * sizeof (dtv_t));
 138
 139   /* Re-initialize the TLS.  */
 140   _dl_allocate_tls_init (TLS_TPADJ (result), true);
 141
 142   return result;
 143 }
 144
 145 /* Return the guard page position on allocated stack.  */
 146 static inline char *
 147 __attribute ((always_inline))
 148 guard_position (void *mem, size_t size, size_t guardsize, struct pthread *pd,
 149                 size_t pagesize_m1)
 150 {
 151 #ifdef NEED_SEPARATE_REGISTER_STACK
 152   return mem + (((size - guardsize) / 2) & ~pagesize_m1);
 153 #elif _STACK_GROWS_DOWN
 154   return mem;
 155 #elif _STACK_GROWS_UP
 156   return (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1);
 157 #endif
 158 }
 159
 160 /* Based on stack allocated with PROT_NONE, setup the required portions with
 161    'prot' flags based on the guard page position.  */
 162 static inline int
 163 setup_stack_prot (char *mem, size_t size, char *guard, size_t guardsize,
 164                   const int prot)
 165 {
 166   char *guardend = guard + guardsize;
 167 #if _STACK_GROWS_DOWN && !defined(NEED_SEPARATE_REGISTER_STACK)
 168   /* As defined at guard_position, for architectures with downward stack
 169      the guard page is always at start of the allocated area.  */
 170   if (__mprotect (guardend, size - guardsize, prot) != 0)
 171     return errno;
 172 #else
 173   size_t mprots1 = (uintptr_t) guard - (uintptr_t) mem;
 174   if (__mprotect (mem, mprots1, prot) != 0)
 175     return errno;
 176   size_t mprots2 = ((uintptr_t) mem + size) - (uintptr_t) guardend;
 177   if (__mprotect (guardend, mprots2, prot) != 0)
 178     return errno;
 179 #endif
 180   return 0;
 181 }
 182
 183 /* Mark the memory of the stack as usable to the kernel.  It frees everything
 184    except for the space used for the TCB itself.  */
 185 static __always_inline void
 186 advise_stack_range (void *mem, size_t size, uintptr_t pd, size_t guardsize)
 187 {
 188   uintptr_t sp = (uintptr_t) CURRENT_STACK_FRAME;
 189   size_t pagesize_m1 = __getpagesize () - 1;
 190 #if _STACK_GROWS_DOWN && !defined(NEED_SEPARATE_REGISTER_STACK)
 191   size_t freesize = (sp - (uintptr_t) mem) & ~pagesize_m1;
 192   assert (freesize < size);
 193   if (freesize > PTHREAD_STACK_MIN)
 194     __madvise (mem, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
 195 #else
 196   /* Page aligned start of memory to free (higher than or equal
 197      to current sp plus the minimum stack size).  */
 198   uintptr_t freeblock = (sp + PTHREAD_STACK_MIN + pagesize_m1) & ~pagesize_m1;
 199   uintptr_t free_end = (pd - guardsize) & ~pagesize_m1;
 200   if (free_end > freeblock)
 201     {
 202       size_t freesize = free_end - freeblock;
 203       assert (freesize < size);
 204       __madvise ((void*) freeblock, freesize, MADV_DONTNEED);
 205     }
 206 #endif
 207 }
 208
 209 /* Returns a usable stack for a new thread either by allocating a
 210    new stack or reusing a cached stack of sufficient size.
 211    ATTR must be non-NULL and point to a valid pthread_attr.
 212    PDP must be non-NULL.  */
 213 static int
 214 allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 215                 void **stack, size_t *stacksize)
 216 {
 217   struct pthread *pd;
 218   size_t size;
 219   size_t pagesize_m1 = __getpagesize () - 1;
 220   size_t tls_static_size_for_stack = __nptl_tls_static_size_for_stack ();
 221   size_t tls_static_align_m1 = GLRO (dl_tls_static_align) - 1;
 222
 223   assert (powerof2 (pagesize_m1 + 1));
 224   assert (TCB_ALIGNMENT >= STACK_ALIGN);
 225
 226   /* Get the stack size from the attribute if it is set.  Otherwise we
 227      use the default we determined at start time.  */
 228   if (attr->stacksize != 0)
 229     size = attr->stacksize;
 230   else
 231     {
 232       lll_lock (__default_pthread_attr_lock, LLL_PRIVATE);
 233       size = __default_pthread_attr.internal.stacksize;
 234       lll_unlock (__default_pthread_attr_lock, LLL_PRIVATE);
 235     }
 236
 237   /* Get memory for the stack.  */
 238   if (__glibc_unlikely (attr->flags & ATTR_FLAG_STACKADDR))
 239     {
 240       uintptr_t adj;
 241       char *stackaddr = (char *) attr->stackaddr;
 242
 243       /* Assume the same layout as the _STACK_GROWS_DOWN case, with struct
 244          pthread at the top of the stack block.  Later we adjust the guard
 245          location and stack address to match the _STACK_GROWS_UP case.  */
 246       if (_STACK_GROWS_UP)
 247         stackaddr += attr->stacksize;
 248
 249       /* If the user also specified the size of the stack make sure it
 250          is large enough.  */
 251       if (attr->stacksize != 0
 252           && attr->stacksize < (tls_static_size_for_stack
 253                                 + MINIMAL_REST_STACK))
 254         return EINVAL;
 255
 256       /* Adjust stack size for alignment of the TLS block.  */
 257 #if TLS_TCB_AT_TP
 258       adj = ((uintptr_t) stackaddr - TLS_TCB_SIZE)
 259             & tls_static_align_m1;
 260       assert (size > adj + TLS_TCB_SIZE);
 261 #elif TLS_DTV_AT_TP
 262       adj = ((uintptr_t) stackaddr - tls_static_size_for_stack)
 263             & tls_static_align_m1;
 264       assert (size > adj);
 265 #endif
 266
 267       /* The user provided some memory.  Let's hope it matches the
 268          size...  We do not allocate guard pages if the user provided
 269          the stack.  It is the user's responsibility to do this if it
 270          is wanted.  */
 271 #if TLS_TCB_AT_TP
 272       pd = (struct pthread *) ((uintptr_t) stackaddr
 273                                - TLS_TCB_SIZE - adj);
 274 #elif TLS_DTV_AT_TP
 275       pd = (struct pthread *) (((uintptr_t) stackaddr
 276                                 - tls_static_size_for_stack - adj)
 277                                - TLS_PRE_TCB_SIZE);
 278 #endif
 279
 280       /* The user provided stack memory needs to be cleared.  */
 281       memset (pd, '\0', sizeof (struct pthread));
 282
 283       /* The first TSD block is included in the TCB.  */
 284       pd->specific[0] = pd->specific_1stblock;
 285
 286       /* Remember the stack-related values.  */
 287       pd->stackblock = (char *) stackaddr - size;
 288       pd->stackblock_size = size;
 289
 290       /* This is a user-provided stack.  It will not be queued in the
 291          stack cache nor will the memory (except the TLS memory) be freed.  */
 292       pd->user_stack = true;
 293
 294       /* This is at least the second thread.  */
 295       pd->header.multiple_threads = 1;
 296
 297 #ifdef NEED_DL_SYSINFO
 298       SETUP_THREAD_SYSINFO (pd);
 299 #endif
 300
 301       /* Don't allow setxid until cloned.  */
 302       pd->setxid_futex = -1;
 303
 304       /* Allocate the DTV for this thread.  */
 305       if (_dl_allocate_tls (TLS_TPADJ (pd)) == NULL)
 306         {
 307           /* Something went wrong.  */
 308           assert (errno == ENOMEM);
 309           return errno;
 310         }
 311
 312
 313       /* Prepare to modify global data.  */
 314       lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 315
 316       /* And add to the list of stacks in use.  */
 317       list_add (&pd->list, &GL (dl_stack_user));
 318
 319       lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 320     }
 321   else
 322     {
 323       /* Allocate some anonymous memory.  If possible use the cache.  */
 324       size_t guardsize;
 325       size_t reported_guardsize;
 326       size_t reqsize;
 327       void *mem;
 328       const int prot = (PROT_READ | PROT_WRITE
 329                         | ((GL(dl_stack_flags) & PF_X) ? PROT_EXEC : 0));
 330
 331       /* Adjust the stack size for alignment.  */
 332       size &= ~tls_static_align_m1;
 333       assert (size != 0);
 334
 335       /* Make sure the size of the stack is enough for the guard and
 336          eventually the thread descriptor.  On some targets there is
 337          a minimum guard size requirement, ARCH_MIN_GUARD_SIZE, so
 338          internally enforce it (unless the guard was disabled), but
 339          report the original guard size for backward compatibility:
 340          before POSIX 2008 the guardsize was specified to be one page
 341          by default which is observable via pthread_attr_getguardsize
 342          and pthread_getattr_np.  */
 343       guardsize = (attr->guardsize + pagesize_m1) & ~pagesize_m1;
 344       reported_guardsize = guardsize;
 345       if (guardsize > 0 && guardsize < ARCH_MIN_GUARD_SIZE)
 346         guardsize = ARCH_MIN_GUARD_SIZE;
 347       if (guardsize < attr->guardsize || size + guardsize < guardsize)
 348         /* Arithmetic overflow.  */
 349         return EINVAL;
 350       size += guardsize;
 351       if (__builtin_expect (size < ((guardsize + tls_static_size_for_stack
 352                                      + MINIMAL_REST_STACK + pagesize_m1)
 353                                     & ~pagesize_m1),
 354                             0))
 355         /* The stack is too small (or the guard too large).  */
 356         return EINVAL;
 357
 358       /* Try to get a stack from the cache.  */
 359       reqsize = size;
 360       pd = get_cached_stack (&size, &mem);
 361       if (pd == NULL)
 362         {
 363           /* If a guard page is required, avoid committing memory by first
 364              allocate with PROT_NONE and then reserve with required permission
 365              excluding the guard page.  */
 366           mem = __mmap (NULL, size, (guardsize == 0) ? prot : PROT_NONE,
 367                         MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
 368
 369           if (__glibc_unlikely (mem == MAP_FAILED))
 370             return errno;
 371
 372           /* SIZE is guaranteed to be greater than zero.
 373              So we can never get a null pointer back from mmap.  */
 374           assert (mem != NULL);
 375
 376           /* Place the thread descriptor at the end of the stack.  */
 377 #if TLS_TCB_AT_TP
 378           pd = (struct pthread *) ((((uintptr_t) mem + size)
 379                                     - TLS_TCB_SIZE)
 380                                    & ~tls_static_align_m1);
 381 #elif TLS_DTV_AT_TP
 382           pd = (struct pthread *) ((((uintptr_t) mem + size
 383                                     - tls_static_size_for_stack)
 384                                     & ~tls_static_align_m1)
 385                                    - TLS_PRE_TCB_SIZE);
 386 #endif
 387
 388           /* Now mprotect the required region excluding the guard area.  */
 389           if (__glibc_likely (guardsize > 0))
 390             {
 391               char *guard = guard_position (mem, size, guardsize, pd,
 392                                             pagesize_m1);
 393               if (setup_stack_prot (mem, size, guard, guardsize, prot) != 0)
 394                 {
 395                   __munmap (mem, size);
 396                   return errno;
 397                 }
 398             }
 399
 400           /* Remember the stack-related values.  */
 401           pd->stackblock = mem;
 402           pd->stackblock_size = size;
 403           /* Update guardsize for newly allocated guardsize to avoid
 404              an mprotect in guard resize below.  */
 405           pd->guardsize = guardsize;
 406
 407           /* We allocated the first block thread-specific data array.
 408              This address will not change for the lifetime of this
 409              descriptor.  */
 410           pd->specific[0] = pd->specific_1stblock;
 411
 412           /* This is at least the second thread.  */
 413           pd->header.multiple_threads = 1;
 414
 415 #ifdef NEED_DL_SYSINFO
 416           SETUP_THREAD_SYSINFO (pd);
 417 #endif
 418
 419           /* Don't allow setxid until cloned.  */
 420           pd->setxid_futex = -1;
 421
 422           /* Allocate the DTV for this thread.  */
 423           if (_dl_allocate_tls (TLS_TPADJ (pd)) == NULL)
 424             {
 425               /* Something went wrong.  */
 426               assert (errno == ENOMEM);
 427
 428               /* Free the stack memory we just allocated.  */
 429               (void) __munmap (mem, size);
 430
 431               return errno;
 432             }
 433
 434
 435           /* Prepare to modify global data.  */
 436           lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 437
 438           /* And add to the list of stacks in use.  */
 439           __nptl_stack_list_add (&pd->list, &GL (dl_stack_used));
 440
 441           lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 442
 443
 444           /* There might have been a race.  Another thread might have
 445              caused the stacks to get exec permission while this new
 446              stack was prepared.  Detect if this was possible and
 447              change the permission if necessary.  */
 448           if (__builtin_expect ((GL(dl_stack_flags) & PF_X) != 0
 449                                 && (prot & PROT_EXEC) == 0, 0))
 450             {
 451               int err = __nptl_change_stack_perm (pd);
 452               if (err != 0)
 453                 {
 454                   /* Free the stack memory we just allocated.  */
 455                   (void) __munmap (mem, size);
 456
 457                   return err;
 458                 }
 459             }
 460
 461
 462           /* Note that all of the stack and the thread descriptor is
 463              zeroed.  This means we do not have to initialize fields
 464              with initial value zero.  This is specifically true for
 465              the 'tid' field which is always set back to zero once the
 466              stack is not used anymore and for the 'guardsize' field
 467              which will be read next.  */
 468         }
 469
 470       /* Create or resize the guard area if necessary.  */
 471       if (__glibc_unlikely (guardsize > pd->guardsize))
 472         {
 473           char *guard = guard_position (mem, size, guardsize, pd,
 474                                         pagesize_m1);
 475           if (__mprotect (guard, guardsize, PROT_NONE) != 0)
 476             {
 477             mprot_error:
 478               lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 479
 480               /* Remove the thread from the list.  */
 481               __nptl_stack_list_del (&pd->list);
 482
 483               lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 484
 485               /* Get rid of the TLS block we allocated.  */
 486               _dl_deallocate_tls (TLS_TPADJ (pd), false);
 487
 488               /* Free the stack memory regardless of whether the size
 489                  of the cache is over the limit or not.  If this piece
 490                  of memory caused problems we better do not use it
 491                  anymore.  Uh, and we ignore possible errors.  There
 492                  is nothing we could do.  */
 493               (void) __munmap (mem, size);
 494
 495               return errno;
 496             }
 497
 498           pd->guardsize = guardsize;
 499         }
 500       else if (__builtin_expect (pd->guardsize - guardsize > size - reqsize,
 501                                  0))
 502         {
 503           /* The old guard area is too large.  */
 504
 505 #ifdef NEED_SEPARATE_REGISTER_STACK
 506           char *guard = mem + (((size - guardsize) / 2) & ~pagesize_m1);
 507           char *oldguard = mem + (((size - pd->guardsize) / 2) & ~pagesize_m1);
 508
 509           if (oldguard < guard
 510               && __mprotect (oldguard, guard - oldguard, prot) != 0)
 511             goto mprot_error;
 512
 513           if (__mprotect (guard + guardsize,
 514                         oldguard + pd->guardsize - guard - guardsize,
 515                         prot) != 0)
 516             goto mprot_error;
 517 #elif _STACK_GROWS_DOWN
 518           if (__mprotect ((char *) mem + guardsize, pd->guardsize - guardsize,
 519                         prot) != 0)
 520             goto mprot_error;
 521 #elif _STACK_GROWS_UP
 522          char *new_guard = (char *)(((uintptr_t) pd - guardsize)
 523                                     & ~pagesize_m1);
 524          char *old_guard = (char *)(((uintptr_t) pd - pd->guardsize)
 525                                     & ~pagesize_m1);
 526          /* The guard size difference might be > 0, but once rounded
 527             to the nearest page the size difference might be zero.  */
 528          if (new_guard > old_guard
 529              && __mprotect (old_guard, new_guard - old_guard, prot) != 0)
 530             goto mprot_error;
 531 #endif
 532
 533           pd->guardsize = guardsize;
 534         }
 535       /* The pthread_getattr_np() calls need to get passed the size
 536          requested in the attribute, regardless of how large the
 537          actually used guardsize is.  */
 538       pd->reported_guardsize = reported_guardsize;
 539     }
 540
 541   /* Initialize the lock.  We have to do this unconditionally since the
 542      stillborn thread could be canceled while the lock is taken.  */
 543   pd->lock = LLL_LOCK_INITIALIZER;
 544
 545   /* The robust mutex lists also need to be initialized
 546      unconditionally because the cleanup for the previous stack owner
 547      might have happened in the kernel.  */
 548   pd->robust_head.futex_offset = (offsetof (pthread_mutex_t, __data.__lock)
 549                                   - offsetof (pthread_mutex_t,
 550                                               __data.__list.__next));
 551   pd->robust_head.list_op_pending = NULL;
 552 #if __PTHREAD_MUTEX_HAVE_PREV
 553   pd->robust_prev = &pd->robust_head;
 554 #endif
 555   pd->robust_head.list = &pd->robust_head;
 556
 557   /* We place the thread descriptor at the end of the stack.  */
 558   *pdp = pd;
 559
 560   void *stacktop;
 561
 562 #if TLS_TCB_AT_TP
 563   /* The stack begins before the TCB and the static TLS block.  */
 564   stacktop = ((char *) (pd + 1) - tls_static_size_for_stack);
 565 #elif TLS_DTV_AT_TP
 566   stacktop = (char *) (pd - 1);
 567 #endif
 568
 569   *stacksize = stacktop - pd->stackblock;
 570   *stack = pd->stackblock;
 571
 572   return 0;
 573 }