kernel/compat.c

   1 /*
   2  *  linux/kernel/compat.c
   3  *
   4  *  Kernel compatibililty routines for e.g. 32 bit syscall support
   5  *  on 64 bit kernels.
   6  *
   7  *  Copyright (C) 2002-2003 Stephen Rothwell, IBM Corporation
   8  *
   9  *  This program is free software; you can redistribute it and/or modify
  10  *  it under the terms of the GNU General Public License version 2 as
  11  *  published by the Free Software Foundation.
  12  */
  13
  14 #include <linux/linkage.h>
  15 #include <linux/compat.h>
  16 #include <linux/errno.h>
  17 #include <linux/time.h>
  18 #include <linux/signal.h>
  19 #include <linux/sched.h>        /* for MAX_SCHEDULE_TIMEOUT */
  20 #include <linux/syscalls.h>
  21 #include <linux/unistd.h>
  22 #include <linux/security.h>
  23 #include <linux/timex.h>
  24 #include <linux/export.h>
  25 #include <linux/migrate.h>
  26 #include <linux/posix-timers.h>
  27 #include <linux/times.h>
  28 #include <linux/ptrace.h>
  29 #include <linux/gfp.h>
  30
  31 #include <linux/uaccess.h>
  32
  33 int compat_get_timex(struct timex *txc, const struct compat_timex __user *utp)
  34 {
  35         struct compat_timex tx32;
  36
  37         if (copy_from_user(&tx32, utp, sizeof(struct compat_timex)))
  38                 return -EFAULT;
  39
  40         txc->modes = tx32.modes;
  41         txc->offset = tx32.offset;
  42         txc->freq = tx32.freq;
  43         txc->maxerror = tx32.maxerror;
  44         txc->esterror = tx32.esterror;
  45         txc->status = tx32.status;
  46         txc->constant = tx32.constant;
  47         txc->precision = tx32.precision;
  48         txc->tolerance = tx32.tolerance;
  49         txc->time.tv_sec = tx32.time.tv_sec;
  50         txc->time.tv_usec = tx32.time.tv_usec;
  51         txc->tick = tx32.tick;
  52         txc->ppsfreq = tx32.ppsfreq;
  53         txc->jitter = tx32.jitter;
  54         txc->shift = tx32.shift;
  55         txc->stabil = tx32.stabil;
  56         txc->jitcnt = tx32.jitcnt;
  57         txc->calcnt = tx32.calcnt;
  58         txc->errcnt = tx32.errcnt;
  59         txc->stbcnt = tx32.stbcnt;
  60
  61         return 0;
  62 }
  63
  64 int compat_put_timex(struct compat_timex __user *utp, const struct timex *txc)
  65 {
  66         struct compat_timex tx32;
  67
  68         memset(&tx32, 0, sizeof(struct compat_timex));
  69         tx32.modes = txc->modes;
  70         tx32.offset = txc->offset;
  71         tx32.freq = txc->freq;
  72         tx32.maxerror = txc->maxerror;
  73         tx32.esterror = txc->esterror;
  74         tx32.status = txc->status;
  75         tx32.constant = txc->constant;
  76         tx32.precision = txc->precision;
  77         tx32.tolerance = txc->tolerance;
  78         tx32.time.tv_sec = txc->time.tv_sec;
  79         tx32.time.tv_usec = txc->time.tv_usec;
  80         tx32.tick = txc->tick;
  81         tx32.ppsfreq = txc->ppsfreq;
  82         tx32.jitter = txc->jitter;
  83         tx32.shift = txc->shift;
  84         tx32.stabil = txc->stabil;
  85         tx32.jitcnt = txc->jitcnt;
  86         tx32.calcnt = txc->calcnt;
  87         tx32.errcnt = txc->errcnt;
  88         tx32.stbcnt = txc->stbcnt;
  89         tx32.tai = txc->tai;
  90         if (copy_to_user(utp, &tx32, sizeof(struct compat_timex)))
  91                 return -EFAULT;
  92         return 0;
  93 }
  94
  95 static int __compat_get_timeval(struct timeval *tv, const struct compat_timeval __user *ctv)
  96 {
  97         return (!access_ok(VERIFY_READ, ctv, sizeof(*ctv)) ||
  98                         __get_user(tv->tv_sec, &ctv->tv_sec) ||
  99                         __get_user(tv->tv_usec, &ctv->tv_usec)) ? -EFAULT : 0;
 100 }
 101
 102 static int __compat_put_timeval(const struct timeval *tv, struct compat_timeval __user *ctv)
 103 {
 104         return (!access_ok(VERIFY_WRITE, ctv, sizeof(*ctv)) ||
 105                         __put_user(tv->tv_sec, &ctv->tv_sec) ||
 106                         __put_user(tv->tv_usec, &ctv->tv_usec)) ? -EFAULT : 0;
 107 }
 108
 109 static int __compat_get_timespec(struct timespec *ts, const struct compat_timespec __user *cts)
 110 {
 111         return (!access_ok(VERIFY_READ, cts, sizeof(*cts)) ||
 112                         __get_user(ts->tv_sec, &cts->tv_sec) ||
 113                         __get_user(ts->tv_nsec, &cts->tv_nsec)) ? -EFAULT : 0;
 114 }
 115
 116 static int __compat_put_timespec(const struct timespec *ts, struct compat_timespec __user *cts)
 117 {
 118         return (!access_ok(VERIFY_WRITE, cts, sizeof(*cts)) ||
 119                         __put_user(ts->tv_sec, &cts->tv_sec) ||
 120                         __put_user(ts->tv_nsec, &cts->tv_nsec)) ? -EFAULT : 0;
 121 }
 122
 123 static int __compat_get_timespec64(struct timespec64 *ts64,
 124                                    const struct compat_timespec __user *cts)
 125 {
 126         struct compat_timespec ts;
 127         int ret;
 128
 129         ret = copy_from_user(&ts, cts, sizeof(ts));
 130         if (ret)
 131                 return -EFAULT;
 132
 133         ts64->tv_sec = ts.tv_sec;
 134         ts64->tv_nsec = ts.tv_nsec;
 135
 136         return 0;
 137 }
 138
 139 static int __compat_put_timespec64(const struct timespec64 *ts64,
 140                                    struct compat_timespec __user *cts)
 141 {
 142         struct compat_timespec ts = {
 143                 .tv_sec = ts64->tv_sec,
 144                 .tv_nsec = ts64->tv_nsec
 145         };
 146         return copy_to_user(cts, &ts, sizeof(ts)) ? -EFAULT : 0;
 147 }
 148
 149 int compat_get_timespec64(struct timespec64 *ts, const void __user *uts)
 150 {
 151         if (COMPAT_USE_64BIT_TIME)
 152                 return copy_from_user(ts, uts, sizeof(*ts)) ? -EFAULT : 0;
 153         else
 154                 return __compat_get_timespec64(ts, uts);
 155 }
 156 EXPORT_SYMBOL_GPL(compat_get_timespec64);
 157
 158 int compat_put_timespec64(const struct timespec64 *ts, void __user *uts)
 159 {
 160         if (COMPAT_USE_64BIT_TIME)
 161                 return copy_to_user(uts, ts, sizeof(*ts)) ? -EFAULT : 0;
 162         else
 163                 return __compat_put_timespec64(ts, uts);
 164 }
 165 EXPORT_SYMBOL_GPL(compat_put_timespec64);
 166
 167 int compat_get_timeval(struct timeval *tv, const void __user *utv)
 168 {
 169         if (COMPAT_USE_64BIT_TIME)
 170                 return copy_from_user(tv, utv, sizeof(*tv)) ? -EFAULT : 0;
 171         else
 172                 return __compat_get_timeval(tv, utv);
 173 }
 174 EXPORT_SYMBOL_GPL(compat_get_timeval);
 175
 176 int compat_put_timeval(const struct timeval *tv, void __user *utv)
 177 {
 178         if (COMPAT_USE_64BIT_TIME)
 179                 return copy_to_user(utv, tv, sizeof(*tv)) ? -EFAULT : 0;
 180         else
 181                 return __compat_put_timeval(tv, utv);
 182 }
 183 EXPORT_SYMBOL_GPL(compat_put_timeval);
 184
 185 int compat_get_timespec(struct timespec *ts, const void __user *uts)
 186 {
 187         if (COMPAT_USE_64BIT_TIME)
 188                 return copy_from_user(ts, uts, sizeof(*ts)) ? -EFAULT : 0;
 189         else
 190                 return __compat_get_timespec(ts, uts);
 191 }
 192 EXPORT_SYMBOL_GPL(compat_get_timespec);
 193
 194 int compat_put_timespec(const struct timespec *ts, void __user *uts)
 195 {
 196         if (COMPAT_USE_64BIT_TIME)
 197                 return copy_to_user(uts, ts, sizeof(*ts)) ? -EFAULT : 0;
 198         else
 199                 return __compat_put_timespec(ts, uts);
 200 }
 201 EXPORT_SYMBOL_GPL(compat_put_timespec);
 202
 203 int get_compat_itimerval(struct itimerval *o, const struct compat_itimerval __user *i)
 204 {
 205         struct compat_itimerval v32;
 206
 207         if (copy_from_user(&v32, i, sizeof(struct compat_itimerval)))
 208                 return -EFAULT;
 209         o->it_interval.tv_sec = v32.it_interval.tv_sec;
 210         o->it_interval.tv_usec = v32.it_interval.tv_usec;
 211         o->it_value.tv_sec = v32.it_value.tv_sec;
 212         o->it_value.tv_usec = v32.it_value.tv_usec;
 213         return 0;
 214 }
 215
 216 int put_compat_itimerval(struct compat_itimerval __user *o, const struct itimerval *i)
 217 {
 218         struct compat_itimerval v32;
 219
 220         v32.it_interval.tv_sec = i->it_interval.tv_sec;
 221         v32.it_interval.tv_usec = i->it_interval.tv_usec;
 222         v32.it_value.tv_sec = i->it_value.tv_sec;
 223         v32.it_value.tv_usec = i->it_value.tv_usec;
 224         return copy_to_user(o, &v32, sizeof(struct compat_itimerval)) ? -EFAULT : 0;
 225 }
 226
 227 #ifdef __ARCH_WANT_SYS_SIGPROCMASK
 228
 229 /*
 230  * sys_sigprocmask SIG_SETMASK sets the first (compat) word of the
 231  * blocked set of signals to the supplied signal set
 232  */
 233 static inline void compat_sig_setmask(sigset_t *blocked, compat_sigset_word set)
 234 {
 235         memcpy(blocked->sig, &set, sizeof(set));
 236 }
 237
 238 COMPAT_SYSCALL_DEFINE3(sigprocmask, int, how,
 239                        compat_old_sigset_t __user *, nset,
 240                        compat_old_sigset_t __user *, oset)
 241 {
 242         old_sigset_t old_set, new_set;
 243         sigset_t new_blocked;
 244
 245         old_set = current->blocked.sig[0];
 246
 247         if (nset) {
 248                 if (get_user(new_set, nset))
 249                         return -EFAULT;
 250                 new_set &= ~(sigmask(SIGKILL) | sigmask(SIGSTOP));
 251
 252                 new_blocked = current->blocked;
 253
 254                 switch (how) {
 255                 case SIG_BLOCK:
 256                         sigaddsetmask(&new_blocked, new_set);
 257                         break;
 258                 case SIG_UNBLOCK:
 259                         sigdelsetmask(&new_blocked, new_set);
 260                         break;
 261                 case SIG_SETMASK:
 262                         compat_sig_setmask(&new_blocked, new_set);
 263                         break;
 264                 default:
 265                         return -EINVAL;
 266                 }
 267
 268                 set_current_blocked(&new_blocked);
 269         }
 270
 271         if (oset) {
 272                 if (put_user(old_set, oset))
 273                         return -EFAULT;
 274         }
 275
 276         return 0;
 277 }
 278
 279 #endif
 280
 281 int put_compat_rusage(const struct rusage *r, struct compat_rusage __user *ru)
 282 {
 283         struct compat_rusage r32;
 284         memset(&r32, 0, sizeof(r32));
 285         r32.ru_utime.tv_sec = r->ru_utime.tv_sec;
 286         r32.ru_utime.tv_usec = r->ru_utime.tv_usec;
 287         r32.ru_stime.tv_sec = r->ru_stime.tv_sec;
 288         r32.ru_stime.tv_usec = r->ru_stime.tv_usec;
 289         r32.ru_maxrss = r->ru_maxrss;
 290         r32.ru_ixrss = r->ru_ixrss;
 291         r32.ru_idrss = r->ru_idrss;
 292         r32.ru_isrss = r->ru_isrss;
 293         r32.ru_minflt = r->ru_minflt;
 294         r32.ru_majflt = r->ru_majflt;
 295         r32.ru_nswap = r->ru_nswap;
 296         r32.ru_inblock = r->ru_inblock;
 297         r32.ru_oublock = r->ru_oublock;
 298         r32.ru_msgsnd = r->ru_msgsnd;
 299         r32.ru_msgrcv = r->ru_msgrcv;
 300         r32.ru_nsignals = r->ru_nsignals;
 301         r32.ru_nvcsw = r->ru_nvcsw;
 302         r32.ru_nivcsw = r->ru_nivcsw;
 303         if (copy_to_user(ru, &r32, sizeof(r32)))
 304                 return -EFAULT;
 305         return 0;
 306 }
 307
 308 static int compat_get_user_cpu_mask(compat_ulong_t __user *user_mask_ptr,
 309                                     unsigned len, struct cpumask *new_mask)
 310 {
 311         unsigned long *k;
 312
 313         if (len < cpumask_size())
 314                 memset(new_mask, 0, cpumask_size());
 315         else if (len > cpumask_size())
 316                 len = cpumask_size();
 317
 318         k = cpumask_bits(new_mask);
 319         return compat_get_bitmap(k, user_mask_ptr, len * 8);
 320 }
 321
 322 COMPAT_SYSCALL_DEFINE3(sched_setaffinity, compat_pid_t, pid,
 323                        unsigned int, len,
 324                        compat_ulong_t __user *, user_mask_ptr)
 325 {
 326         cpumask_var_t new_mask;
 327         int retval;
 328
 329         if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
 330                 return -ENOMEM;
 331
 332         retval = compat_get_user_cpu_mask(user_mask_ptr, len, new_mask);
 333         if (retval)
 334                 goto out;
 335
 336         retval = sched_setaffinity(pid, new_mask);
 337 out:
 338         free_cpumask_var(new_mask);
 339         return retval;
 340 }
 341
 342 COMPAT_SYSCALL_DEFINE3(sched_getaffinity, compat_pid_t,  pid, unsigned int, len,
 343                        compat_ulong_t __user *, user_mask_ptr)
 344 {
 345         int ret;
 346         cpumask_var_t mask;
 347
 348         if ((len * BITS_PER_BYTE) < nr_cpu_ids)
 349                 return -EINVAL;
 350         if (len & (sizeof(compat_ulong_t)-1))
 351                 return -EINVAL;
 352
 353         if (!alloc_cpumask_var(&mask, GFP_KERNEL))
 354                 return -ENOMEM;
 355
 356         ret = sched_getaffinity(pid, mask);
 357         if (ret == 0) {
 358                 size_t retlen = min_t(size_t, len, cpumask_size());
 359
 360                 if (compat_put_bitmap(user_mask_ptr, cpumask_bits(mask), retlen * 8))
 361                         ret = -EFAULT;
 362                 else
 363                         ret = retlen;
 364         }
 365         free_cpumask_var(mask);
 366
 367         return ret;
 368 }
 369
 370 int get_compat_itimerspec(struct itimerspec *dst,
 371                           const struct compat_itimerspec __user *src)
 372 {
 373         if (__compat_get_timespec(&dst->it_interval, &src->it_interval) ||
 374             __compat_get_timespec(&dst->it_value, &src->it_value))
 375                 return -EFAULT;
 376         return 0;
 377 }
 378
 379 int put_compat_itimerspec(struct compat_itimerspec __user *dst,
 380                           const struct itimerspec *src)
 381 {
 382         if (__compat_put_timespec(&src->it_interval, &dst->it_interval) ||
 383             __compat_put_timespec(&src->it_value, &dst->it_value))
 384                 return -EFAULT;
 385         return 0;
 386 }
 387
 388 int get_compat_itimerspec64(struct itimerspec64 *its,
 389                         const struct compat_itimerspec __user *uits)
 390 {
 391
 392         if (__compat_get_timespec64(&its->it_interval, &uits->it_interval) ||
 393             __compat_get_timespec64(&its->it_value, &uits->it_value))
 394                 return -EFAULT;
 395         return 0;
 396 }
 397 EXPORT_SYMBOL_GPL(get_compat_itimerspec64);
 398
 399 int put_compat_itimerspec64(const struct itimerspec64 *its,
 400                         struct compat_itimerspec __user *uits)
 401 {
 402         if (__compat_put_timespec64(&its->it_interval, &uits->it_interval) ||
 403             __compat_put_timespec64(&its->it_value, &uits->it_value))
 404                 return -EFAULT;
 405         return 0;
 406 }
 407 EXPORT_SYMBOL_GPL(put_compat_itimerspec64);
 408
 409 /*
 410  * We currently only need the following fields from the sigevent
 411  * structure: sigev_value, sigev_signo, sig_notify and (sometimes
 412  * sigev_notify_thread_id).  The others are handled in user mode.
 413  * We also assume that copying sigev_value.sival_int is sufficient
 414  * to keep all the bits of sigev_value.sival_ptr intact.
 415  */
 416 int get_compat_sigevent(struct sigevent *event,
 417                 const struct compat_sigevent __user *u_event)
 418 {
 419         memset(event, 0, sizeof(*event));
 420         return (!access_ok(VERIFY_READ, u_event, sizeof(*u_event)) ||
 421                 __get_user(event->sigev_value.sival_int,
 422                         &u_event->sigev_value.sival_int) ||
 423                 __get_user(event->sigev_signo, &u_event->sigev_signo) ||
 424                 __get_user(event->sigev_notify, &u_event->sigev_notify) ||
 425                 __get_user(event->sigev_notify_thread_id,
 426                         &u_event->sigev_notify_thread_id))
 427                 ? -EFAULT : 0;
 428 }
 429
 430 long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
 431                        unsigned long bitmap_size)
 432 {
 433         unsigned long nr_compat_longs;
 434
 435         /* align bitmap up to nearest compat_long_t boundary */
 436         bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
 437         nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
 438
 439         if (!access_ok(VERIFY_READ, umask, bitmap_size / 8))
 440                 return -EFAULT;
 441
 442         user_access_begin();
 443         while (nr_compat_longs > 1) {
 444                 compat_ulong_t l1, l2;
 445                 unsafe_get_user(l1, umask++, Efault);
 446                 unsafe_get_user(l2, umask++, Efault);
 447                 *mask++ = ((unsigned long)l2 << BITS_PER_COMPAT_LONG) | l1;
 448                 nr_compat_longs -= 2;
 449         }
 450         if (nr_compat_longs)
 451                 unsafe_get_user(*mask, umask++, Efault);
 452         user_access_end();
 453         return 0;
 454
 455 Efault:
 456         user_access_end();
 457         return -EFAULT;
 458 }
 459
 460 long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
 461                        unsigned long bitmap_size)
 462 {
 463         unsigned long nr_compat_longs;
 464
 465         /* align bitmap up to nearest compat_long_t boundary */
 466         bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
 467         nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
 468
 469         if (!access_ok(VERIFY_WRITE, umask, bitmap_size / 8))
 470                 return -EFAULT;
 471
 472         user_access_begin();
 473         while (nr_compat_longs > 1) {
 474                 unsigned long m = *mask++;
 475                 unsafe_put_user((compat_ulong_t)m, umask++, Efault);
 476                 unsafe_put_user(m >> BITS_PER_COMPAT_LONG, umask++, Efault);
 477                 nr_compat_longs -= 2;
 478         }
 479         if (nr_compat_longs)
 480                 unsafe_put_user((compat_ulong_t)*mask, umask++, Efault);
 481         user_access_end();
 482         return 0;
 483 Efault:
 484         user_access_end();
 485         return -EFAULT;
 486 }
 487
 488 void
 489 sigset_from_compat(sigset_t *set, const compat_sigset_t *compat)
 490 {
 491         switch (_NSIG_WORDS) {
 492         case 4: set->sig[3] = compat->sig[6] | (((long)compat->sig[7]) << 32 );
 493         case 3: set->sig[2] = compat->sig[4] | (((long)compat->sig[5]) << 32 );
 494         case 2: set->sig[1] = compat->sig[2] | (((long)compat->sig[3]) << 32 );
 495         case 1: set->sig[0] = compat->sig[0] | (((long)compat->sig[1]) << 32 );
 496         }
 497 }
 498 EXPORT_SYMBOL_GPL(sigset_from_compat);
 499
 500 void
 501 sigset_to_compat(compat_sigset_t *compat, const sigset_t *set)
 502 {
 503         switch (_NSIG_WORDS) {
 504         case 4: compat->sig[7] = (set->sig[3] >> 32); compat->sig[6] = set->sig[3];
 505         case 3: compat->sig[5] = (set->sig[2] >> 32); compat->sig[4] = set->sig[2];
 506         case 2: compat->sig[3] = (set->sig[1] >> 32); compat->sig[2] = set->sig[1];
 507         case 1: compat->sig[1] = (set->sig[0] >> 32); compat->sig[0] = set->sig[0];
 508         }
 509 }
 510
 511 #ifdef CONFIG_NUMA
 512 COMPAT_SYSCALL_DEFINE6(move_pages, pid_t, pid, compat_ulong_t, nr_pages,
 513                        compat_uptr_t __user *, pages32,
 514                        const int __user *, nodes,
 515                        int __user *, status,
 516                        int, flags)
 517 {
 518         const void __user * __user *pages;
 519         int i;
 520
 521         pages = compat_alloc_user_space(nr_pages * sizeof(void *));
 522         for (i = 0; i < nr_pages; i++) {
 523                 compat_uptr_t p;
 524
 525                 if (get_user(p, pages32 + i) ||
 526                         put_user(compat_ptr(p), pages + i))
 527                         return -EFAULT;
 528         }
 529         return sys_move_pages(pid, nr_pages, pages, nodes, status, flags);
 530 }
 531
 532 COMPAT_SYSCALL_DEFINE4(migrate_pages, compat_pid_t, pid,
 533                        compat_ulong_t, maxnode,
 534                        const compat_ulong_t __user *, old_nodes,
 535                        const compat_ulong_t __user *, new_nodes)
 536 {
 537         unsigned long __user *old = NULL;
 538         unsigned long __user *new = NULL;
 539         nodemask_t tmp_mask;
 540         unsigned long nr_bits;
 541         unsigned long size;
 542
 543         nr_bits = min_t(unsigned long, maxnode - 1, MAX_NUMNODES);
 544         size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
 545         if (old_nodes) {
 546                 if (compat_get_bitmap(nodes_addr(tmp_mask), old_nodes, nr_bits))
 547                         return -EFAULT;
 548                 old = compat_alloc_user_space(new_nodes ? size * 2 : size);
 549                 if (new_nodes)
 550                         new = old + size / sizeof(unsigned long);
 551                 if (copy_to_user(old, nodes_addr(tmp_mask), size))
 552                         return -EFAULT;
 553         }
 554         if (new_nodes) {
 555                 if (compat_get_bitmap(nodes_addr(tmp_mask), new_nodes, nr_bits))
 556                         return -EFAULT;
 557                 if (new == NULL)
 558                         new = compat_alloc_user_space(size);
 559                 if (copy_to_user(new, nodes_addr(tmp_mask), size))
 560                         return -EFAULT;
 561         }
 562         return sys_migrate_pages(pid, nr_bits + 1, old, new);
 563 }
 564 #endif
 565
 566 COMPAT_SYSCALL_DEFINE2(sched_rr_get_interval,
 567                        compat_pid_t, pid,
 568                        struct compat_timespec __user *, interval)
 569 {
 570         struct timespec t;
 571         int ret;
 572         mm_segment_t old_fs = get_fs();
 573
 574         set_fs(KERNEL_DS);
 575         ret = sys_sched_rr_get_interval(pid, (struct timespec __user *)&t);
 576         set_fs(old_fs);
 577         if (compat_put_timespec(&t, interval))
 578                 return -EFAULT;
 579         return ret;
 580 }
 581
 582 /*
 583  * Allocate user-space memory for the duration of a single system call,
 584  * in order to marshall parameters inside a compat thunk.
 585  */
 586 void __user *compat_alloc_user_space(unsigned long len)
 587 {
 588         void __user *ptr;
 589
 590         /* If len would occupy more than half of the entire compat space... */
 591         if (unlikely(len > (((compat_uptr_t)~0) >> 1)))
 592                 return NULL;
 593
 594         ptr = arch_compat_alloc_user_space(len);
 595
 596         if (unlikely(!access_ok(VERIFY_WRITE, ptr, len)))
 597                 return NULL;
 598
 599         return ptr;
 600 }
 601 EXPORT_SYMBOL_GPL(compat_alloc_user_space);