osfmk/i386/user_ldt.c

   1 /*
   2  * Copyright (c) 2000-2009 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28 /*
  29  * @OSF_COPYRIGHT@
  30  */
  31 /*
  32  * Mach Operating System
  33  * Copyright (c) 1991 Carnegie Mellon University
  34  * All Rights Reserved.
  35  *
  36  * Permission to use, copy, modify and distribute this software and its
  37  * documentation is hereby granted, provided that both the copyright
  38  * notice and this permission notice appear in all copies of the
  39  * software, derivative works or modified versions, and any portions
  40  * thereof, and that both notices appear in supporting documentation.
  41  *
  42  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  43  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
  44  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  45  *
  46  * Carnegie Mellon requests users of this software to return to
  47  *
  48  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  49  *  School of Computer Science
  50  *  Carnegie Mellon University
  51  *  Pittsburgh PA 15213-3890
  52  *
  53  * any improvements or extensions that they make and grant Carnegie Mellon
  54  * the rights to redistribute these changes.
  55  */
  56
  57 /*
  58  */
  59
  60 /*
  61  * User LDT management.
  62  * Each task may have its own LDT.
  63  */
  64
  65 #include <kern/kalloc.h>
  66 #include <kern/thread.h>
  67 #include <kern/misc_protos.h>
  68
  69 #include <vm/vm_kern.h>
  70
  71 #include <i386/machdep_call.h>
  72 #include <i386/user_ldt.h>
  73 #include <i386/mp.h>
  74 #include <i386/machine_routines.h>
  75 #include <i386/proc_reg.h>
  76 #include <i386/mp_desc.h>
  77 #include <i386/seg.h>
  78 #include <i386/thread.h>
  79
  80 #include <sys/errno.h>
  81
  82 static void user_ldt_set_action(void *);
  83
  84 /*
  85  * Add the descriptors to the LDT, starting with
  86  * the descriptor for 'first_selector'.
  87  */
  88
  89 int
  90 i386_set_ldt(
  91         uint32_t                *retval,
  92         uint32_t                start_sel,
  93         uint32_t                descs,  /* out */
  94         uint32_t                num_sels)
  95 {
  96         user_ldt_t      new_ldt, old_ldt;
  97         struct real_descriptor *dp;
  98         unsigned int    i;
  99         unsigned int    min_selector = LDTSZ_MIN;       /* do not allow the system selectors to be changed */
 100         task_t          task = current_task();
 101         unsigned int    ldt_count;
 102         kern_return_t err;
 103
 104         if (start_sel != LDT_AUTO_ALLOC
 105             && (start_sel != 0 || num_sels != 0)
 106             && (start_sel < min_selector || start_sel >= LDTSZ))
 107             return EINVAL;
 108         if (start_sel != LDT_AUTO_ALLOC
 109             && (uint64_t)start_sel + (uint64_t)num_sels > LDTSZ) /* cast to uint64_t to detect wrap-around */
 110             return EINVAL;
 111
 112         task_lock(task);
 113
 114         old_ldt = task->i386_ldt;
 115
 116         if (start_sel == LDT_AUTO_ALLOC) {
 117             if (old_ldt) {
 118                 unsigned int null_count;
 119                 struct real_descriptor null_ldt;
 120
 121                 bzero(&null_ldt, sizeof(null_ldt));
 122
 123                 /*
 124                  * Look for null selectors among the already-allocated
 125                  * entries.
 126                  */
 127                 null_count = 0;
 128                 i = 0;
 129                 while (i < old_ldt->count)
 130                 {
 131                     if (!memcmp(&old_ldt->ldt[i++], &null_ldt, sizeof(null_ldt))) {
 132                         null_count++;
 133                         if (null_count == num_sels)
 134                             break;  /* break out of while loop */
 135                     } else {
 136                         null_count = 0;
 137                     }
 138                 }
 139
 140                 /*
 141                  * If we broke out of the while loop, i points to the selector
 142                  * after num_sels null selectors.  Otherwise it points to the end
 143                  * of the old LDTs, and null_count is the number of null selectors
 144                  * at the end.
 145                  *
 146                  * Either way, there are null_count null selectors just prior to
 147                  * the i-indexed selector, and either null_count >= num_sels,
 148                  * or we're at the end, so we can extend.
 149                  */
 150                 start_sel = old_ldt->start + i - null_count;
 151             } else {
 152                 start_sel = LDTSZ_MIN;
 153             }
 154
 155             if ((uint64_t)start_sel + (uint64_t)num_sels > LDTSZ) {
 156                 task_unlock(task);
 157                 return ENOMEM;
 158             }
 159         }
 160
 161         if (start_sel == 0 && num_sels == 0) {
 162             new_ldt = NULL;
 163         } else {
 164             /*
 165              * Allocate new LDT
 166              */
 167
 168             unsigned int    begin_sel = start_sel;
 169             unsigned int    end_sel = begin_sel + num_sels;
 170
 171             if (old_ldt != NULL) {
 172                 if (old_ldt->start < begin_sel)
 173                     begin_sel = old_ldt->start;
 174                 if (old_ldt->start + old_ldt->count > end_sel)
 175                     end_sel = old_ldt->start + old_ldt->count;
 176             }
 177
 178             ldt_count = end_sel - begin_sel;
 179             /* XXX allocation under task lock */
 180             new_ldt = (user_ldt_t)kalloc(sizeof(struct user_ldt) + (ldt_count * sizeof(struct real_descriptor)));
 181             if (new_ldt == NULL) {
 182                 task_unlock(task);
 183                 return ENOMEM;
 184             }
 185
 186             new_ldt->start = begin_sel;
 187             new_ldt->count = ldt_count;
 188
 189             /*
 190              * Have new LDT.  If there was a an old ldt, copy descriptors
 191              * from old to new.
 192              */
 193             if (old_ldt) {
 194                 bcopy(&old_ldt->ldt[0],
 195                       &new_ldt->ldt[old_ldt->start - begin_sel],
 196                       old_ldt->count * sizeof(struct real_descriptor));
 197
 198                 /*
 199                  * If the old and new LDTs are non-overlapping, fill the
 200                  * center in with null selectors.
 201                  */
 202
 203                 if (old_ldt->start + old_ldt->count < start_sel)
 204                     bzero(&new_ldt->ldt[old_ldt->count],
 205                           (start_sel - (old_ldt->start + old_ldt->count)) * sizeof(struct real_descriptor));
 206                 else if (old_ldt->start > start_sel + num_sels)
 207                     bzero(&new_ldt->ldt[num_sels],
 208                           (old_ldt->start - (start_sel + num_sels)) * sizeof(struct real_descriptor));
 209             }
 210
 211             /*
 212              * Install new descriptors.
 213              */
 214             if (descs != 0) {
 215                     /* XXX copyin under task lock */
 216                 err = copyin(descs, (char *)&new_ldt->ldt[start_sel - begin_sel],
 217                              num_sels * sizeof(struct real_descriptor));
 218                 if (err != 0)
 219                 {
 220                     task_unlock(task);
 221                     user_ldt_free(new_ldt);
 222                     return err;
 223                 }
 224             } else {
 225                 bzero(&new_ldt->ldt[start_sel - begin_sel], num_sels * sizeof(struct real_descriptor));
 226             }
 227
 228             /*
 229              * Validate descriptors.
 230              * Only allow descriptors with user privileges.
 231              */
 232             for (i = 0, dp = (struct real_descriptor *) &new_ldt->ldt[start_sel - begin_sel];
 233                  i < num_sels;
 234                  i++, dp++)
 235             {
 236                 switch (dp->access & ~ACC_A) {
 237                     case 0:
 238                     case ACC_P:
 239                         /* valid empty descriptor, clear Present preemptively */
 240                         dp->access &= (~ACC_P & 0xff);
 241                         break;
 242                     case ACC_P | ACC_PL_U | ACC_DATA:
 243                     case ACC_P | ACC_PL_U | ACC_DATA_W:
 244                     case ACC_P | ACC_PL_U | ACC_DATA_E:
 245                     case ACC_P | ACC_PL_U | ACC_DATA_EW:
 246                     case ACC_P | ACC_PL_U | ACC_CODE:
 247                     case ACC_P | ACC_PL_U | ACC_CODE_R:
 248                     case ACC_P | ACC_PL_U | ACC_CODE_C:
 249                     case ACC_P | ACC_PL_U | ACC_CODE_CR:
 250                         break;
 251                     default:
 252                         task_unlock(task);
 253                         user_ldt_free(new_ldt);
 254                         return EACCES;
 255                 }
 256             }
 257         }
 258
 259         task->i386_ldt = new_ldt; /* new LDT for task */
 260
 261         /*
 262          * Switch to new LDT.  We need to do this on all CPUs, since
 263          * another thread in this same task may be currently running,
 264          * and we need to make sure the new LDT is in place
 265          * throughout the task before returning to the user.
 266          */
 267         mp_broadcast(user_ldt_set_action, task);
 268
 269         task_unlock(task);
 270
 271         /* free old LDT.  We can't do this until after we've
 272          * rendezvoused with all CPUs, in case another thread
 273          * in this task was in the process of context switching.
 274          */
 275         if (old_ldt)
 276             user_ldt_free(old_ldt);
 277
 278         *retval = start_sel;
 279
 280         return 0;
 281 }
 282
 283 int
 284 i386_get_ldt(
 285         uint32_t                *retval,
 286         uint32_t                start_sel,
 287         uint32_t                descs,  /* out */
 288         uint32_t                num_sels)
 289 {
 290         user_ldt_t      user_ldt;
 291         task_t          task = current_task();
 292         unsigned int    ldt_count;
 293         kern_return_t   err;
 294
 295         if (start_sel >= 8192)
 296             return EINVAL;
 297         if ((uint64_t)start_sel + (uint64_t)num_sels > 8192)
 298             return EINVAL;
 299         if (descs == 0)
 300             return EINVAL;
 301
 302         task_lock(task);
 303
 304         user_ldt = task->i386_ldt;
 305         err = 0;
 306
 307         /*
 308          * copy out the descriptors
 309          */
 310
 311         if (user_ldt != 0)
 312             ldt_count = user_ldt->start + user_ldt->count;
 313         else
 314             ldt_count = LDTSZ_MIN;
 315
 316
 317         if (start_sel < ldt_count)
 318         {
 319             unsigned int copy_sels = num_sels;
 320
 321             if (start_sel + num_sels > ldt_count)
 322                 copy_sels = ldt_count - start_sel;
 323
 324             err = copyout((char *)(current_ldt() + start_sel),
 325                           descs, copy_sels * sizeof(struct real_descriptor));
 326         }
 327
 328         task_unlock(task);
 329
 330         *retval = ldt_count;
 331
 332         return err;
 333 }
 334
 335 void
 336 user_ldt_free(
 337         user_ldt_t      user_ldt)
 338 {
 339         kfree(user_ldt, sizeof(struct user_ldt) + (user_ldt->count * sizeof(struct real_descriptor)));
 340 }
 341
 342 user_ldt_t
 343 user_ldt_copy(
 344         user_ldt_t      user_ldt)
 345 {
 346         if (user_ldt != NULL) {
 347             size_t      size = sizeof(struct user_ldt) + (user_ldt->count * sizeof(struct real_descriptor));
 348             user_ldt_t  new_ldt = (user_ldt_t)kalloc(size);
 349             if (new_ldt != NULL)
 350                 bcopy(user_ldt, new_ldt, size);
 351             return new_ldt;
 352         }
 353
 354         return 0;
 355 }
 356
 357 void
 358 user_ldt_set_action(
 359         void *arg)
 360 {
 361         task_t          arg_task = (task_t)arg;
 362
 363         if (arg_task == current_task()) {
 364             user_ldt_set(current_thread());
 365         }
 366 }
 367
 368 /*
 369  * Set the LDT for the given thread on the current CPU.  Should be invoked
 370  * with interrupts disabled.
 371  */
 372 void
 373 user_ldt_set(
 374         thread_t thread)
 375 {
 376         task_t          task = thread->task;
 377         user_ldt_t      user_ldt;
 378
 379         user_ldt = task->i386_ldt;
 380
 381         if (user_ldt != 0) {
 382             struct real_descriptor *ldtp = (struct real_descriptor *)current_ldt();
 383
 384             if (user_ldt->start > LDTSZ_MIN) {
 385                 bzero(&ldtp[LDTSZ_MIN],
 386                       sizeof(struct real_descriptor) * (user_ldt->start - LDTSZ_MIN));
 387             }
 388
 389             bcopy(user_ldt->ldt, &ldtp[user_ldt->start],
 390                   sizeof(struct real_descriptor) * (user_ldt->count));
 391
 392             gdt_desc_p(USER_LDT)->limit_low = (uint16_t)((sizeof(struct real_descriptor) * (user_ldt->start + user_ldt->count)) - 1);
 393
 394             ml_cpu_set_ldt(USER_LDT);
 395         } else {
 396             ml_cpu_set_ldt(KERNEL_LDT);
 397         }
 398 }