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