tools/testing/selftests/x86/ldt_gdt.c

   1 /*
   2  * ldt_gdt.c - Test cases for LDT and GDT access
   3  * Copyright (c) 2015 Andrew Lutomirski
   4  */
   5
   6 #define _GNU_SOURCE
   7 #include <err.h>
   8 #include <stdio.h>
   9 #include <stdint.h>
  10 #include <signal.h>
  11 #include <setjmp.h>
  12 #include <stdlib.h>
  13 #include <string.h>
  14 #include <errno.h>
  15 #include <unistd.h>
  16 #include <sys/syscall.h>
  17 #include <asm/ldt.h>
  18 #include <sys/types.h>
  19 #include <sys/wait.h>
  20 #include <stdbool.h>
  21 #include <pthread.h>
  22 #include <sched.h>
  23 #include <linux/futex.h>
  24
  25 #define AR_ACCESSED             (1<<8)
  26
  27 #define AR_TYPE_RODATA          (0 * (1<<9))
  28 #define AR_TYPE_RWDATA          (1 * (1<<9))
  29 #define AR_TYPE_RODATA_EXPDOWN  (2 * (1<<9))
  30 #define AR_TYPE_RWDATA_EXPDOWN  (3 * (1<<9))
  31 #define AR_TYPE_XOCODE          (4 * (1<<9))
  32 #define AR_TYPE_XRCODE          (5 * (1<<9))
  33 #define AR_TYPE_XOCODE_CONF     (6 * (1<<9))
  34 #define AR_TYPE_XRCODE_CONF     (7 * (1<<9))
  35
  36 #define AR_DPL3                 (3 * (1<<13))
  37
  38 #define AR_S                    (1 << 12)
  39 #define AR_P                    (1 << 15)
  40 #define AR_AVL                  (1 << 20)
  41 #define AR_L                    (1 << 21)
  42 #define AR_DB                   (1 << 22)
  43 #define AR_G                    (1 << 23)
  44
  45 static int nerrs;
  46
  47 static void check_invalid_segment(uint16_t index, int ldt)
  48 {
  49         uint32_t has_limit = 0, has_ar = 0, limit, ar;
  50         uint32_t selector = (index << 3) | (ldt << 2) | 3;
  51
  52         asm ("lsl %[selector], %[limit]\n\t"
  53              "jnz 1f\n\t"
  54              "movl $1, %[has_limit]\n\t"
  55              "1:"
  56              : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
  57              : [selector] "r" (selector));
  58         asm ("larl %[selector], %[ar]\n\t"
  59              "jnz 1f\n\t"
  60              "movl $1, %[has_ar]\n\t"
  61              "1:"
  62              : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
  63              : [selector] "r" (selector));
  64
  65         if (has_limit || has_ar) {
  66                 printf("[FAIL]\t%s entry %hu is valid but should be invalid\n",
  67                        (ldt ? "LDT" : "GDT"), index);
  68                 nerrs++;
  69         } else {
  70                 printf("[OK]\t%s entry %hu is invalid\n",
  71                        (ldt ? "LDT" : "GDT"), index);
  72         }
  73 }
  74
  75 static void check_valid_segment(uint16_t index, int ldt,
  76                                 uint32_t expected_ar, uint32_t expected_limit,
  77                                 bool verbose)
  78 {
  79         uint32_t has_limit = 0, has_ar = 0, limit, ar;
  80         uint32_t selector = (index << 3) | (ldt << 2) | 3;
  81
  82         asm ("lsl %[selector], %[limit]\n\t"
  83              "jnz 1f\n\t"
  84              "movl $1, %[has_limit]\n\t"
  85              "1:"
  86              : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
  87              : [selector] "r" (selector));
  88         asm ("larl %[selector], %[ar]\n\t"
  89              "jnz 1f\n\t"
  90              "movl $1, %[has_ar]\n\t"
  91              "1:"
  92              : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
  93              : [selector] "r" (selector));
  94
  95         if (!has_limit || !has_ar) {
  96                 printf("[FAIL]\t%s entry %hu is invalid but should be valid\n",
  97                        (ldt ? "LDT" : "GDT"), index);
  98                 nerrs++;
  99                 return;
 100         }
 101
 102         if (ar != expected_ar) {
 103                 printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
 104                        (ldt ? "LDT" : "GDT"), index, ar, expected_ar);
 105                 nerrs++;
 106         } else if (limit != expected_limit) {
 107                 printf("[FAIL]\t%s entry %hu has limit 0x%08X but expected 0x%08X\n",
 108                        (ldt ? "LDT" : "GDT"), index, limit, expected_limit);
 109                 nerrs++;
 110         } else if (verbose) {
 111                 printf("[OK]\t%s entry %hu has AR 0x%08X and limit 0x%08X\n",
 112                        (ldt ? "LDT" : "GDT"), index, ar, limit);
 113         }
 114 }
 115
 116 static bool install_valid_mode(const struct user_desc *desc, uint32_t ar,
 117                                bool oldmode)
 118 {
 119         int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
 120                           desc, sizeof(*desc));
 121         if (ret < -1)
 122                 errno = -ret;
 123         if (ret == 0) {
 124                 uint32_t limit = desc->limit;
 125                 if (desc->limit_in_pages)
 126                         limit = (limit << 12) + 4095;
 127                 check_valid_segment(desc->entry_number, 1, ar, limit, true);
 128                 return true;
 129         } else if (errno == ENOSYS) {
 130                 printf("[OK]\tmodify_ldt returned -ENOSYS\n");
 131                 return false;
 132         } else {
 133                 if (desc->seg_32bit) {
 134                         printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
 135                                errno);
 136                         nerrs++;
 137                         return false;
 138                 } else {
 139                         printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
 140                         return false;
 141                 }
 142         }
 143 }
 144
 145 static bool install_valid(const struct user_desc *desc, uint32_t ar)
 146 {
 147         return install_valid_mode(desc, ar, false);
 148 }
 149
 150 static void install_invalid(const struct user_desc *desc, bool oldmode)
 151 {
 152         int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
 153                           desc, sizeof(*desc));
 154         if (ret < -1)
 155                 errno = -ret;
 156         if (ret == 0) {
 157                 check_invalid_segment(desc->entry_number, 1);
 158         } else if (errno == ENOSYS) {
 159                 printf("[OK]\tmodify_ldt returned -ENOSYS\n");
 160         } else {
 161                 if (desc->seg_32bit) {
 162                         printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
 163                                errno);
 164                         nerrs++;
 165                 } else {
 166                         printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
 167                 }
 168         }
 169 }
 170
 171 static int safe_modify_ldt(int func, struct user_desc *ptr,
 172                            unsigned long bytecount)
 173 {
 174         int ret = syscall(SYS_modify_ldt, 0x11, ptr, bytecount);
 175         if (ret < -1)
 176                 errno = -ret;
 177         return ret;
 178 }
 179
 180 static void fail_install(struct user_desc *desc)
 181 {
 182         if (safe_modify_ldt(0x11, desc, sizeof(*desc)) == 0) {
 183                 printf("[FAIL]\tmodify_ldt accepted a bad descriptor\n");
 184                 nerrs++;
 185         } else if (errno == ENOSYS) {
 186                 printf("[OK]\tmodify_ldt returned -ENOSYS\n");
 187         } else {
 188                 printf("[OK]\tmodify_ldt failure %d\n", errno);
 189         }
 190 }
 191
 192 static void do_simple_tests(void)
 193 {
 194         struct user_desc desc = {
 195                 .entry_number    = 0,
 196                 .base_addr       = 0,
 197                 .limit           = 10,
 198                 .seg_32bit       = 1,
 199                 .contents        = 2, /* Code, not conforming */
 200                 .read_exec_only  = 0,
 201                 .limit_in_pages  = 0,
 202                 .seg_not_present = 0,
 203                 .useable         = 0
 204         };
 205         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);
 206
 207         desc.limit_in_pages = 1;
 208         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 209                       AR_S | AR_P | AR_DB | AR_G);
 210
 211         check_invalid_segment(1, 1);
 212
 213         desc.entry_number = 2;
 214         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 215                       AR_S | AR_P | AR_DB | AR_G);
 216
 217         check_invalid_segment(1, 1);
 218
 219         desc.base_addr = 0xf0000000;
 220         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 221                       AR_S | AR_P | AR_DB | AR_G);
 222
 223         desc.useable = 1;
 224         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 225                       AR_S | AR_P | AR_DB | AR_G | AR_AVL);
 226
 227         desc.seg_not_present = 1;
 228         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 229                       AR_S | AR_DB | AR_G | AR_AVL);
 230
 231         desc.seg_32bit = 0;
 232         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 233                       AR_S | AR_G | AR_AVL);
 234
 235         desc.seg_32bit = 1;
 236         desc.contents = 0;
 237         install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA |
 238                       AR_S | AR_DB | AR_G | AR_AVL);
 239
 240         desc.read_exec_only = 1;
 241         install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA |
 242                       AR_S | AR_DB | AR_G | AR_AVL);
 243
 244         desc.contents = 1;
 245         install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA_EXPDOWN |
 246                       AR_S | AR_DB | AR_G | AR_AVL);
 247
 248         desc.read_exec_only = 0;
 249         desc.limit_in_pages = 0;
 250         install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA_EXPDOWN |
 251                       AR_S | AR_DB | AR_AVL);
 252
 253         desc.contents = 3;
 254         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE_CONF |
 255                       AR_S | AR_DB | AR_AVL);
 256
 257         desc.read_exec_only = 1;
 258         install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE_CONF |
 259                       AR_S | AR_DB | AR_AVL);
 260
 261         desc.read_exec_only = 0;
 262         desc.contents = 2;
 263         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
 264                       AR_S | AR_DB | AR_AVL);
 265
 266         desc.read_exec_only = 1;
 267
 268 #ifdef __x86_64__
 269         desc.lm = 1;
 270         install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
 271                       AR_S | AR_DB | AR_AVL);
 272         desc.lm = 0;
 273 #endif
 274
 275         bool entry1_okay = install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
 276                                          AR_S | AR_DB | AR_AVL);
 277
 278         if (entry1_okay) {
 279                 printf("[RUN]\tTest fork\n");
 280                 pid_t child = fork();
 281                 if (child == 0) {
 282                         nerrs = 0;
 283                         check_valid_segment(desc.entry_number, 1,
 284                                             AR_DPL3 | AR_TYPE_XOCODE |
 285                                             AR_S | AR_DB | AR_AVL, desc.limit,
 286                                             true);
 287                         check_invalid_segment(1, 1);
 288                         exit(nerrs ? 1 : 0);
 289                 } else {
 290                         int status;
 291                         if (waitpid(child, &status, 0) != child ||
 292                             !WIFEXITED(status)) {
 293                                 printf("[FAIL]\tChild died\n");
 294                                 nerrs++;
 295                         } else if (WEXITSTATUS(status) != 0) {
 296                                 printf("[FAIL]\tChild failed\n");
 297                                 nerrs++;
 298                         } else {
 299                                 printf("[OK]\tChild succeeded\n");
 300                         }
 301                 }
 302
 303                 printf("[RUN]\tTest size\n");
 304                 int i;
 305                 for (i = 0; i < 8192; i++) {
 306                         desc.entry_number = i;
 307                         desc.limit = i;
 308                         if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
 309                                 printf("[FAIL]\tFailed to install entry %d\n", i);
 310                                 nerrs++;
 311                                 break;
 312                         }
 313                 }
 314                 for (int j = 0; j < i; j++) {
 315                         check_valid_segment(j, 1, AR_DPL3 | AR_TYPE_XOCODE |
 316                                             AR_S | AR_DB | AR_AVL, j, false);
 317                 }
 318                 printf("[DONE]\tSize test\n");
 319         } else {
 320                 printf("[SKIP]\tSkipping fork and size tests because we have no LDT\n");
 321         }
 322
 323         /* Test entry_number too high. */
 324         desc.entry_number = 8192;
 325         fail_install(&desc);
 326
 327         /* Test deletion and actions mistakeable for deletion. */
 328         memset(&desc, 0, sizeof(desc));
 329         install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P);
 330
 331         desc.seg_not_present = 1;
 332         install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);
 333
 334         desc.seg_not_present = 0;
 335         desc.read_exec_only = 1;
 336         install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S | AR_P);
 337
 338         desc.read_exec_only = 0;
 339         desc.seg_not_present = 1;
 340         install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);
 341
 342         desc.read_exec_only = 1;
 343         desc.limit = 1;
 344         install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);
 345
 346         desc.limit = 0;
 347         desc.base_addr = 1;
 348         install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);
 349
 350         desc.base_addr = 0;
 351         install_invalid(&desc, false);
 352
 353         desc.seg_not_present = 0;
 354         desc.read_exec_only = 0;
 355         desc.seg_32bit = 1;
 356         install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P | AR_DB);
 357         install_invalid(&desc, true);
 358 }
 359
 360 /*
 361  * 0: thread is idle
 362  * 1: thread armed
 363  * 2: thread should clear LDT entry 0
 364  * 3: thread should exit
 365  */
 366 static volatile unsigned int ftx;
 367
 368 static void *threadproc(void *ctx)
 369 {
 370         cpu_set_t cpuset;
 371         CPU_ZERO(&cpuset);
 372         CPU_SET(1, &cpuset);
 373         if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
 374                 err(1, "sched_setaffinity to CPU 1");   /* should never fail */
 375
 376         while (1) {
 377                 syscall(SYS_futex, &ftx, FUTEX_WAIT, 0, NULL, NULL, 0);
 378                 while (ftx != 2) {
 379                         if (ftx >= 3)
 380                                 return NULL;
 381                 }
 382
 383                 /* clear LDT entry 0 */
 384                 const struct user_desc desc = {};
 385                 if (syscall(SYS_modify_ldt, 1, &desc, sizeof(desc)) != 0)
 386                         err(1, "modify_ldt");
 387
 388                 /* If ftx == 2, set it to zero.  If ftx == 100, quit. */
 389                 unsigned int x = -2;
 390                 asm volatile ("lock xaddl %[x], %[ftx]" :
 391                               [x] "+r" (x), [ftx] "+m" (ftx));
 392                 if (x != 2)
 393                         return NULL;
 394         }
 395 }
 396
 397 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 398                        int flags)
 399 {
 400         struct sigaction sa;
 401         memset(&sa, 0, sizeof(sa));
 402         sa.sa_sigaction = handler;
 403         sa.sa_flags = SA_SIGINFO | flags;
 404         sigemptyset(&sa.sa_mask);
 405         if (sigaction(sig, &sa, 0))
 406                 err(1, "sigaction");
 407
 408 }
 409
 410 static jmp_buf jmpbuf;
 411
 412 static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
 413 {
 414         siglongjmp(jmpbuf, 1);
 415 }
 416
 417 static void do_multicpu_tests(void)
 418 {
 419         cpu_set_t cpuset;
 420         pthread_t thread;
 421         int failures = 0, iters = 5, i;
 422         unsigned short orig_ss;
 423
 424         CPU_ZERO(&cpuset);
 425         CPU_SET(1, &cpuset);
 426         if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
 427                 printf("[SKIP]\tCannot set affinity to CPU 1\n");
 428                 return;
 429         }
 430
 431         CPU_ZERO(&cpuset);
 432         CPU_SET(0, &cpuset);
 433         if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
 434                 printf("[SKIP]\tCannot set affinity to CPU 0\n");
 435                 return;
 436         }
 437
 438         sethandler(SIGSEGV, sigsegv, 0);
 439 #ifdef __i386__
 440         /* True 32-bit kernels send SIGILL instead of SIGSEGV on IRET faults. */
 441         sethandler(SIGILL, sigsegv, 0);
 442 #endif
 443
 444         printf("[RUN]\tCross-CPU LDT invalidation\n");
 445
 446         if (pthread_create(&thread, 0, threadproc, 0) != 0)
 447                 err(1, "pthread_create");
 448
 449         asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));
 450
 451         for (i = 0; i < 5; i++) {
 452                 if (sigsetjmp(jmpbuf, 1) != 0)
 453                         continue;
 454
 455                 /* Make sure the thread is ready after the last test. */
 456                 while (ftx != 0)
 457                         ;
 458
 459                 struct user_desc desc = {
 460                         .entry_number    = 0,
 461                         .base_addr       = 0,
 462                         .limit           = 0xfffff,
 463                         .seg_32bit       = 1,
 464                         .contents        = 0, /* Data */
 465                         .read_exec_only  = 0,
 466                         .limit_in_pages  = 1,
 467                         .seg_not_present = 0,
 468                         .useable         = 0
 469                 };
 470
 471                 if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
 472                         if (errno != ENOSYS)
 473                                 err(1, "modify_ldt");
 474                         printf("[SKIP]\tmodify_ldt unavailable\n");
 475                         break;
 476                 }
 477
 478                 /* Arm the thread. */
 479                 ftx = 1;
 480                 syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
 481
 482                 asm volatile ("mov %0, %%ss" : : "r" (0x7));
 483
 484                 /* Go! */
 485                 ftx = 2;
 486
 487                 while (ftx != 0)
 488                         ;
 489
 490                 /*
 491                  * On success, modify_ldt will segfault us synchronously,
 492                  * and we'll escape via siglongjmp.
 493                  */
 494
 495                 failures++;
 496                 asm volatile ("mov %0, %%ss" : : "rm" (orig_ss));
 497         };
 498
 499         ftx = 100;  /* Kill the thread. */
 500         syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
 501
 502         if (pthread_join(thread, NULL) != 0)
 503                 err(1, "pthread_join");
 504
 505         if (failures) {
 506                 printf("[FAIL]\t%d of %d iterations failed\n", failures, iters);
 507                 nerrs++;
 508         } else {
 509                 printf("[OK]\tAll %d iterations succeeded\n", iters);
 510         }
 511 }
 512
 513 static int finish_exec_test(void)
 514 {
 515         /*
 516          * In a sensible world, this would be check_invalid_segment(0, 1);
 517          * For better or for worse, though, the LDT is inherited across exec.
 518          * We can probably change this safely, but for now we test it.
 519          */
 520         check_valid_segment(0, 1,
 521                             AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB,
 522                             42, true);
 523
 524         return nerrs ? 1 : 0;
 525 }
 526
 527 static void do_exec_test(void)
 528 {
 529         printf("[RUN]\tTest exec\n");
 530
 531         struct user_desc desc = {
 532                 .entry_number    = 0,
 533                 .base_addr       = 0,
 534                 .limit           = 42,
 535                 .seg_32bit       = 1,
 536                 .contents        = 2, /* Code, not conforming */
 537                 .read_exec_only  = 0,
 538                 .limit_in_pages  = 0,
 539                 .seg_not_present = 0,
 540                 .useable         = 0
 541         };
 542         install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);
 543
 544         pid_t child = fork();
 545         if (child == 0) {
 546                 execl("/proc/self/exe", "ldt_gdt_test_exec", NULL);
 547                 printf("[FAIL]\tCould not exec self\n");
 548                 exit(1);        /* exec failed */
 549         } else {
 550                 int status;
 551                 if (waitpid(child, &status, 0) != child ||
 552                     !WIFEXITED(status)) {
 553                         printf("[FAIL]\tChild died\n");
 554                         nerrs++;
 555                 } else if (WEXITSTATUS(status) != 0) {
 556                         printf("[FAIL]\tChild failed\n");
 557                         nerrs++;
 558                 } else {
 559                         printf("[OK]\tChild succeeded\n");
 560                 }
 561         }
 562 }
 563
 564 int main(int argc, char **argv)
 565 {
 566         if (argc == 1 && !strcmp(argv[0], "ldt_gdt_test_exec"))
 567                 return finish_exec_test();
 568
 569         do_simple_tests();
 570
 571         do_multicpu_tests();
 572
 573         do_exec_test();
 574
 575         return nerrs ? 1 : 0;
 576 }