src/shared/efivars.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <dirent.h>
   4 #include <errno.h>
   5 #include <fcntl.h>
   6 #include <limits.h>
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10 #include <sys/stat.h>
  11 #include <unistd.h>
  12
  13 #include "sd-id128.h"
  14
  15 #include "alloc-util.h"
  16 #include "dirent-util.h"
  17 #include "efivars.h"
  18 #include "fd-util.h"
  19 #include "io-util.h"
  20 #include "macro.h"
  21 #include "parse-util.h"
  22 #include "stdio-util.h"
  23 #include "time-util.h"
  24 #include "utf8.h"
  25 #include "util.h"
  26 #include "virt.h"
  27
  28 #if ENABLE_EFI
  29
  30 #define LOAD_OPTION_ACTIVE            0x00000001
  31 #define MEDIA_DEVICE_PATH                   0x04
  32 #define MEDIA_HARDDRIVE_DP                  0x01
  33 #define MEDIA_FILEPATH_DP                   0x04
  34 #define SIGNATURE_TYPE_GUID                 0x02
  35 #define MBR_TYPE_EFI_PARTITION_TABLE_HEADER 0x02
  36 #define END_DEVICE_PATH_TYPE                0x7f
  37 #define END_ENTIRE_DEVICE_PATH_SUBTYPE      0xff
  38 #define EFI_OS_INDICATIONS_BOOT_TO_FW_UI    0x0000000000000001
  39
  40 struct boot_option {
  41         uint32_t attr;
  42         uint16_t path_len;
  43         uint16_t title[];
  44 } _packed_;
  45
  46 struct drive_path {
  47         uint32_t part_nr;
  48         uint64_t part_start;
  49         uint64_t part_size;
  50         char signature[16];
  51         uint8_t mbr_type;
  52         uint8_t signature_type;
  53 } _packed_;
  54
  55 struct device_path {
  56         uint8_t type;
  57         uint8_t sub_type;
  58         uint16_t length;
  59         union {
  60                 uint16_t path[0];
  61                 struct drive_path drive;
  62         };
  63 } _packed_;
  64
  65 bool is_efi_boot(void) {
  66         return access("/sys/firmware/efi", F_OK) >= 0;
  67 }
  68
  69 static int read_flag(const char *varname) {
  70         _cleanup_free_ void *v = NULL;
  71         uint8_t b;
  72         size_t s;
  73         int r;
  74
  75         r = efi_get_variable(EFI_VENDOR_GLOBAL, varname, NULL, &v, &s);
  76         if (r < 0)
  77                 return r;
  78
  79         if (s != 1)
  80                 return -EINVAL;
  81
  82         b = *(uint8_t *)v;
  83         return b > 0;
  84 }
  85
  86 bool is_efi_secure_boot(void) {
  87         return read_flag("SecureBoot") > 0;
  88 }
  89
  90 bool is_efi_secure_boot_setup_mode(void) {
  91         return read_flag("SetupMode") > 0;
  92 }
  93
  94 int efi_reboot_to_firmware_supported(void) {
  95         _cleanup_free_ void *v = NULL;
  96         uint64_t b;
  97         size_t s;
  98         int r;
  99
 100         if (!is_efi_boot() || detect_container() > 0)
 101                 return -EOPNOTSUPP;
 102
 103         r = efi_get_variable(EFI_VENDOR_GLOBAL, "OsIndicationsSupported", NULL, &v, &s);
 104         if (r == -ENOENT) /* variable doesn't exist? it's not supported then */
 105                 return -EOPNOTSUPP;
 106         if (r < 0)
 107                 return r;
 108         if (s != sizeof(uint64_t))
 109                 return -EINVAL;
 110
 111         b = *(uint64_t*) v;
 112         if (!(b & EFI_OS_INDICATIONS_BOOT_TO_FW_UI))
 113                 return -EOPNOTSUPP; /* bit unset? it's not supported then */
 114
 115         return 0;
 116 }
 117
 118 static int get_os_indications(uint64_t *os_indication) {
 119         _cleanup_free_ void *v = NULL;
 120         size_t s;
 121         int r;
 122
 123         r = efi_reboot_to_firmware_supported();
 124         if (r < 0)
 125                 return r;
 126
 127         r = efi_get_variable(EFI_VENDOR_GLOBAL, "OsIndications", NULL, &v, &s);
 128         if (r == -ENOENT) {
 129                 /* Some firmware implementations that do support
 130                  * OsIndications and report that with
 131                  * OsIndicationsSupported will remove the
 132                  * OsIndications variable when it is unset. Let's
 133                  * pretend it's 0 then, to hide this implementation
 134                  * detail. Note that this call will return -ENOENT
 135                  * then only if the support for OsIndications is
 136                  * missing entirely, as determined by
 137                  * efi_reboot_to_firmware_supported() above. */
 138                 *os_indication = 0;
 139                 return 0;
 140         } else if (r < 0)
 141                 return r;
 142         else if (s != sizeof(uint64_t))
 143                 return -EINVAL;
 144
 145         *os_indication = *(uint64_t *)v;
 146         return 0;
 147 }
 148
 149 int efi_get_reboot_to_firmware(void) {
 150         int r;
 151         uint64_t b;
 152
 153         r = get_os_indications(&b);
 154         if (r < 0)
 155                 return r;
 156
 157         return !!(b & EFI_OS_INDICATIONS_BOOT_TO_FW_UI);
 158 }
 159
 160 int efi_set_reboot_to_firmware(bool value) {
 161         int r;
 162         uint64_t b, b_new;
 163
 164         r = get_os_indications(&b);
 165         if (r < 0)
 166                 return r;
 167
 168         if (value)
 169                 b_new = b | EFI_OS_INDICATIONS_BOOT_TO_FW_UI;
 170         else
 171                 b_new = b & ~EFI_OS_INDICATIONS_BOOT_TO_FW_UI;
 172
 173         /* Avoid writing to efi vars store if we can due to firmware bugs. */
 174         if (b != b_new)
 175                 return efi_set_variable(EFI_VENDOR_GLOBAL, "OsIndications", &b_new, sizeof(uint64_t));
 176
 177         return 0;
 178 }
 179
 180 int efi_get_variable(
 181                 sd_id128_t vendor,
 182                 const char *name,
 183                 uint32_t *attribute,
 184                 void **value,
 185                 size_t *size) {
 186
 187         _cleanup_close_ int fd = -1;
 188         _cleanup_free_ char *p = NULL;
 189         uint32_t a;
 190         ssize_t n;
 191         struct stat st;
 192         _cleanup_free_ void *buf = NULL;
 193
 194         assert(name);
 195         assert(value);
 196         assert(size);
 197
 198         if (asprintf(&p,
 199                      "/sys/firmware/efi/efivars/%s-%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
 200                      name, SD_ID128_FORMAT_VAL(vendor)) < 0)
 201                 return -ENOMEM;
 202
 203         fd = open(p, O_RDONLY|O_NOCTTY|O_CLOEXEC);
 204         if (fd < 0)
 205                 return -errno;
 206
 207         if (fstat(fd, &st) < 0)
 208                 return -errno;
 209         if (st.st_size < 4)
 210                 return -EIO;
 211         if (st.st_size > 4*1024*1024 + 4)
 212                 return -E2BIG;
 213
 214         n = read(fd, &a, sizeof(a));
 215         if (n < 0)
 216                 return -errno;
 217         if (n != sizeof(a))
 218                 return -EIO;
 219
 220         buf = malloc(st.st_size - 4 + 2);
 221         if (!buf)
 222                 return -ENOMEM;
 223
 224         n = read(fd, buf, (size_t) st.st_size - 4);
 225         if (n < 0)
 226                 return -errno;
 227         if (n != (ssize_t) st.st_size - 4)
 228                 return -EIO;
 229
 230         /* Always NUL terminate (2 bytes, to protect UTF-16) */
 231         ((char*) buf)[st.st_size - 4] = 0;
 232         ((char*) buf)[st.st_size - 4 + 1] = 0;
 233
 234         *value = TAKE_PTR(buf);
 235         *size = (size_t) st.st_size - 4;
 236
 237         if (attribute)
 238                 *attribute = a;
 239
 240         return 0;
 241 }
 242
 243 int efi_set_variable(
 244                 sd_id128_t vendor,
 245                 const char *name,
 246                 const void *value,
 247                 size_t size) {
 248
 249         struct var {
 250                 uint32_t attr;
 251                 char buf[];
 252         } _packed_ * _cleanup_free_ buf = NULL;
 253         _cleanup_free_ char *p = NULL;
 254         _cleanup_close_ int fd = -1;
 255
 256         assert(name);
 257         assert(value || size == 0);
 258
 259         if (asprintf(&p,
 260                      "/sys/firmware/efi/efivars/%s-%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
 261                      name, SD_ID128_FORMAT_VAL(vendor)) < 0)
 262                 return -ENOMEM;
 263
 264         if (size == 0) {
 265                 if (unlink(p) < 0)
 266                         return -errno;
 267                 return 0;
 268         }
 269
 270         fd = open(p, O_WRONLY|O_CREAT|O_NOCTTY|O_CLOEXEC, 0644);
 271         if (fd < 0)
 272                 return -errno;
 273
 274         buf = malloc(sizeof(uint32_t) + size);
 275         if (!buf)
 276                 return -ENOMEM;
 277
 278         buf->attr = EFI_VARIABLE_NON_VOLATILE|EFI_VARIABLE_BOOTSERVICE_ACCESS|EFI_VARIABLE_RUNTIME_ACCESS;
 279         memcpy(buf->buf, value, size);
 280
 281         return loop_write(fd, buf, sizeof(uint32_t) + size, false);
 282 }
 283
 284 int efi_get_variable_string(sd_id128_t vendor, const char *name, char **p) {
 285         _cleanup_free_ void *s = NULL;
 286         size_t ss = 0;
 287         int r;
 288         char *x;
 289
 290         r = efi_get_variable(vendor, name, NULL, &s, &ss);
 291         if (r < 0)
 292                 return r;
 293
 294         x = utf16_to_utf8(s, ss);
 295         if (!x)
 296                 return -ENOMEM;
 297
 298         *p = x;
 299         return 0;
 300 }
 301
 302 static size_t utf16_size(const uint16_t *s) {
 303         size_t l = 0;
 304
 305         while (s[l] > 0)
 306                 l++;
 307
 308         return (l+1) * sizeof(uint16_t);
 309 }
 310
 311 static void efi_guid_to_id128(const void *guid, sd_id128_t *id128) {
 312         struct uuid {
 313                 uint32_t u1;
 314                 uint16_t u2;
 315                 uint16_t u3;
 316                 uint8_t u4[8];
 317         } _packed_;
 318         const struct uuid *uuid = guid;
 319
 320         id128->bytes[0] = (uuid->u1 >> 24) & 0xff;
 321         id128->bytes[1] = (uuid->u1 >> 16) & 0xff;
 322         id128->bytes[2] = (uuid->u1 >> 8) & 0xff;
 323         id128->bytes[3] = (uuid->u1) & 0xff;
 324         id128->bytes[4] = (uuid->u2 >> 8) & 0xff;
 325         id128->bytes[5] = (uuid->u2) & 0xff;
 326         id128->bytes[6] = (uuid->u3 >> 8) & 0xff;
 327         id128->bytes[7] = (uuid->u3) & 0xff;
 328         memcpy(&id128->bytes[8], uuid->u4, sizeof(uuid->u4));
 329 }
 330
 331 int efi_get_boot_option(
 332                 uint16_t id,
 333                 char **title,
 334                 sd_id128_t *part_uuid,
 335                 char **path,
 336                 bool *active) {
 337
 338         char boot_id[9];
 339         _cleanup_free_ uint8_t *buf = NULL;
 340         size_t l;
 341         struct boot_option *header;
 342         size_t title_size;
 343         _cleanup_free_ char *s = NULL, *p = NULL;
 344         sd_id128_t p_uuid = SD_ID128_NULL;
 345         int r;
 346
 347         xsprintf(boot_id, "Boot%04X", id);
 348         r = efi_get_variable(EFI_VENDOR_GLOBAL, boot_id, NULL, (void **)&buf, &l);
 349         if (r < 0)
 350                 return r;
 351         if (l < sizeof(struct boot_option))
 352                 return -ENOENT;
 353
 354         header = (struct boot_option *)buf;
 355         title_size = utf16_size(header->title);
 356         if (title_size > l - offsetof(struct boot_option, title))
 357                 return -EINVAL;
 358
 359         if (title) {
 360                 s = utf16_to_utf8(header->title, title_size);
 361                 if (!s)
 362                         return -ENOMEM;
 363         }
 364
 365         if (header->path_len > 0) {
 366                 uint8_t *dbuf;
 367                 size_t dnext;
 368
 369                 dbuf = buf + offsetof(struct boot_option, title) + title_size;
 370                 dnext = 0;
 371                 while (dnext < header->path_len) {
 372                         struct device_path *dpath;
 373
 374                         dpath = (struct device_path *)(dbuf + dnext);
 375                         if (dpath->length < 4)
 376                                 break;
 377
 378                         /* Type 0x7F – End of Hardware Device Path, Sub-Type 0xFF – End Entire Device Path */
 379                         if (dpath->type == END_DEVICE_PATH_TYPE && dpath->sub_type == END_ENTIRE_DEVICE_PATH_SUBTYPE)
 380                                 break;
 381
 382                         dnext += dpath->length;
 383
 384                         /* Type 0x04 – Media Device Path */
 385                         if (dpath->type != MEDIA_DEVICE_PATH)
 386                                 continue;
 387
 388                         /* Sub-Type 1 – Hard Drive */
 389                         if (dpath->sub_type == MEDIA_HARDDRIVE_DP) {
 390                                 /* 0x02 – GUID Partition Table */
 391                                 if (dpath->drive.mbr_type != MBR_TYPE_EFI_PARTITION_TABLE_HEADER)
 392                                         continue;
 393
 394                                 /* 0x02 – GUID signature */
 395                                 if (dpath->drive.signature_type != SIGNATURE_TYPE_GUID)
 396                                         continue;
 397
 398                                 if (part_uuid)
 399                                         efi_guid_to_id128(dpath->drive.signature, &p_uuid);
 400                                 continue;
 401                         }
 402
 403                         /* Sub-Type 4 – File Path */
 404                         if (dpath->sub_type == MEDIA_FILEPATH_DP && !p && path) {
 405                                 p = utf16_to_utf8(dpath->path, dpath->length-4);
 406                                 efi_tilt_backslashes(p);
 407                                 continue;
 408                         }
 409                 }
 410         }
 411
 412         if (title)
 413                 *title = TAKE_PTR(s);
 414         if (part_uuid)
 415                 *part_uuid = p_uuid;
 416         if (path)
 417                 *path = TAKE_PTR(p);
 418         if (active)
 419                 *active = !!(header->attr & LOAD_OPTION_ACTIVE);
 420
 421         return 0;
 422 }
 423
 424 static void to_utf16(uint16_t *dest, const char *src) {
 425         int i;
 426
 427         for (i = 0; src[i] != '\0'; i++)
 428                 dest[i] = src[i];
 429         dest[i] = '\0';
 430 }
 431
 432 struct guid {
 433         uint32_t u1;
 434         uint16_t u2;
 435         uint16_t u3;
 436         uint8_t u4[8];
 437 } _packed_;
 438
 439 static void id128_to_efi_guid(sd_id128_t id, void *guid) {
 440         struct guid *uuid = guid;
 441
 442         uuid->u1 = id.bytes[0] << 24 | id.bytes[1] << 16 | id.bytes[2] << 8 | id.bytes[3];
 443         uuid->u2 = id.bytes[4] << 8 | id.bytes[5];
 444         uuid->u3 = id.bytes[6] << 8 | id.bytes[7];
 445         memcpy(uuid->u4, id.bytes+8, sizeof(uuid->u4));
 446 }
 447
 448 static uint16_t *tilt_slashes(uint16_t *s) {
 449         uint16_t *p;
 450
 451         for (p = s; *p; p++)
 452                 if (*p == '/')
 453                         *p = '\\';
 454
 455         return s;
 456 }
 457
 458 int efi_add_boot_option(uint16_t id, const char *title,
 459                         uint32_t part, uint64_t pstart, uint64_t psize,
 460                         sd_id128_t part_uuid, const char *path) {
 461         char boot_id[9];
 462         size_t size;
 463         size_t title_len;
 464         size_t path_len;
 465         struct boot_option *option;
 466         struct device_path *devicep;
 467         _cleanup_free_ char *buf = NULL;
 468
 469         title_len = (strlen(title)+1) * 2;
 470         path_len = (strlen(path)+1) * 2;
 471
 472         buf = calloc(sizeof(struct boot_option) + title_len +
 473                      sizeof(struct drive_path) +
 474                      sizeof(struct device_path) + path_len, 1);
 475         if (!buf)
 476                 return -ENOMEM;
 477
 478         /* header */
 479         option = (struct boot_option *)buf;
 480         option->attr = LOAD_OPTION_ACTIVE;
 481         option->path_len = offsetof(struct device_path, drive) + sizeof(struct drive_path) +
 482                            offsetof(struct device_path, path) + path_len +
 483                            offsetof(struct device_path, path);
 484         to_utf16(option->title, title);
 485         size = offsetof(struct boot_option, title) + title_len;
 486
 487         /* partition info */
 488         devicep = (struct device_path *)(buf + size);
 489         devicep->type = MEDIA_DEVICE_PATH;
 490         devicep->sub_type = MEDIA_HARDDRIVE_DP;
 491         devicep->length = offsetof(struct device_path, drive) + sizeof(struct drive_path);
 492         devicep->drive.part_nr = part;
 493         devicep->drive.part_start = pstart;
 494         devicep->drive.part_size = psize;
 495         devicep->drive.signature_type = SIGNATURE_TYPE_GUID;
 496         devicep->drive.mbr_type = MBR_TYPE_EFI_PARTITION_TABLE_HEADER;
 497         id128_to_efi_guid(part_uuid, devicep->drive.signature);
 498         size += devicep->length;
 499
 500         /* path to loader */
 501         devicep = (struct device_path *)(buf + size);
 502         devicep->type = MEDIA_DEVICE_PATH;
 503         devicep->sub_type = MEDIA_FILEPATH_DP;
 504         devicep->length = offsetof(struct device_path, path) + path_len;
 505         to_utf16(devicep->path, path);
 506         tilt_slashes(devicep->path);
 507         size += devicep->length;
 508
 509         /* end of path */
 510         devicep = (struct device_path *)(buf + size);
 511         devicep->type = END_DEVICE_PATH_TYPE;
 512         devicep->sub_type = END_ENTIRE_DEVICE_PATH_SUBTYPE;
 513         devicep->length = offsetof(struct device_path, path);
 514         size += devicep->length;
 515
 516         xsprintf(boot_id, "Boot%04X", id);
 517         return efi_set_variable(EFI_VENDOR_GLOBAL, boot_id, buf, size);
 518 }
 519
 520 int efi_remove_boot_option(uint16_t id) {
 521         char boot_id[9];
 522
 523         xsprintf(boot_id, "Boot%04X", id);
 524         return efi_set_variable(EFI_VENDOR_GLOBAL, boot_id, NULL, 0);
 525 }
 526
 527 int efi_get_boot_order(uint16_t **order) {
 528         _cleanup_free_ void *buf = NULL;
 529         size_t l;
 530         int r;
 531
 532         r = efi_get_variable(EFI_VENDOR_GLOBAL, "BootOrder", NULL, &buf, &l);
 533         if (r < 0)
 534                 return r;
 535
 536         if (l <= 0)
 537                 return -ENOENT;
 538
 539         if (l % sizeof(uint16_t) > 0 ||
 540             l / sizeof(uint16_t) > INT_MAX)
 541                 return -EINVAL;
 542
 543         *order = TAKE_PTR(buf);
 544         return (int) (l / sizeof(uint16_t));
 545 }
 546
 547 int efi_set_boot_order(uint16_t *order, size_t n) {
 548         return efi_set_variable(EFI_VENDOR_GLOBAL, "BootOrder", order, n * sizeof(uint16_t));
 549 }
 550
 551 static int boot_id_hex(const char s[4]) {
 552         int i;
 553         int id = 0;
 554
 555         for (i = 0; i < 4; i++)
 556                 if (s[i] >= '0' && s[i] <= '9')
 557                         id |= (s[i] - '0') << (3 - i) * 4;
 558                 else if (s[i] >= 'A' && s[i] <= 'F')
 559                         id |= (s[i] - 'A' + 10) << (3 - i) * 4;
 560                 else
 561                         return -EINVAL;
 562
 563         return id;
 564 }
 565
 566 static int cmp_uint16(const uint16_t *a, const uint16_t *b) {
 567         return CMP(*a, *b);
 568 }
 569
 570 int efi_get_boot_options(uint16_t **options) {
 571         _cleanup_closedir_ DIR *dir = NULL;
 572         struct dirent *de;
 573         _cleanup_free_ uint16_t *list = NULL;
 574         size_t alloc = 0;
 575         int count = 0;
 576
 577         assert(options);
 578
 579         dir = opendir("/sys/firmware/efi/efivars/");
 580         if (!dir)
 581                 return -errno;
 582
 583         FOREACH_DIRENT(de, dir, return -errno) {
 584                 int id;
 585
 586                 if (strncmp(de->d_name, "Boot", 4) != 0)
 587                         continue;
 588
 589                 if (strlen(de->d_name) != 45)
 590                         continue;
 591
 592                 if (strcmp(de->d_name + 8, "-8be4df61-93ca-11d2-aa0d-00e098032b8c") != 0)
 593                         continue;
 594
 595                 id = boot_id_hex(de->d_name + 4);
 596                 if (id < 0)
 597                         continue;
 598
 599                 if (!GREEDY_REALLOC(list, alloc, count + 1))
 600                         return -ENOMEM;
 601
 602                 list[count++] = id;
 603         }
 604
 605         typesafe_qsort(list, count, cmp_uint16);
 606
 607         *options = TAKE_PTR(list);
 608
 609         return count;
 610 }
 611
 612 static int read_usec(sd_id128_t vendor, const char *name, usec_t *u) {
 613         _cleanup_free_ char *j = NULL;
 614         int r;
 615         uint64_t x = 0;
 616
 617         assert(name);
 618         assert(u);
 619
 620         r = efi_get_variable_string(EFI_VENDOR_LOADER, name, &j);
 621         if (r < 0)
 622                 return r;
 623
 624         r = safe_atou64(j, &x);
 625         if (r < 0)
 626                 return r;
 627
 628         *u = x;
 629         return 0;
 630 }
 631
 632 int efi_loader_get_boot_usec(usec_t *firmware, usec_t *loader) {
 633         uint64_t x, y;
 634         int r;
 635
 636         assert(firmware);
 637         assert(loader);
 638
 639         r = read_usec(EFI_VENDOR_LOADER, "LoaderTimeInitUSec", &x);
 640         if (r < 0)
 641                 return r;
 642
 643         r = read_usec(EFI_VENDOR_LOADER, "LoaderTimeExecUSec", &y);
 644         if (r < 0)
 645                 return r;
 646
 647         if (y == 0 || y < x)
 648                 return -EIO;
 649
 650         if (y > USEC_PER_HOUR)
 651                 return -EIO;
 652
 653         *firmware = x;
 654         *loader = y;
 655
 656         return 0;
 657 }
 658
 659 int efi_loader_get_device_part_uuid(sd_id128_t *u) {
 660         _cleanup_free_ char *p = NULL;
 661         int r, parsed[16];
 662
 663         r = efi_get_variable_string(EFI_VENDOR_LOADER, "LoaderDevicePartUUID", &p);
 664         if (r < 0)
 665                 return r;
 666
 667         if (sscanf(p, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
 668                    &parsed[0], &parsed[1], &parsed[2], &parsed[3],
 669                    &parsed[4], &parsed[5], &parsed[6], &parsed[7],
 670                    &parsed[8], &parsed[9], &parsed[10], &parsed[11],
 671                    &parsed[12], &parsed[13], &parsed[14], &parsed[15]) != 16)
 672                 return -EIO;
 673
 674         if (u) {
 675                 unsigned i;
 676
 677                 for (i = 0; i < ELEMENTSOF(parsed); i++)
 678                         u->bytes[i] = parsed[i];
 679         }
 680
 681         return 0;
 682 }
 683
 684 #endif
 685
 686 char *efi_tilt_backslashes(char *s) {
 687         char *p;
 688
 689         for (p = s; *p; p++)
 690                 if (*p == '\\')
 691                         *p = '/';
 692
 693         return s;
 694 }