usr.bin/elfctl/elfctl.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause
   3  *
   4  * Copyright (c) 2019 The FreeBSD Foundation.
   5  *
   6  * This software was developed by Bora Ozarslan under sponsorship from
   7  * the FreeBSD Foundation.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  28  * SUCH DAMAGE.
  29  */
  30
  31 #include <sys/param.h>
  32 #include <sys/elf_common.h>
  33 #include <sys/endian.h>
  34 #include <sys/stat.h>
  35
  36 #include <ctype.h>
  37 #include <err.h>
  38 #include <errno.h>
  39 #include <fcntl.h>
  40 #include <gelf.h>
  41 #include <getopt.h>
  42 #include <libelf.h>
  43 #include <stdbool.h>
  44 #include <stdint.h>
  45 #include <stdio.h>
  46 #include <stdlib.h>
  47 #include <string.h>
  48 #include <unistd.h>
  49
  50 #include "_elftc.h"
  51
  52 __FBSDID("$FreeBSD$");
  53
  54 static bool convert_to_feature_val(const char *, uint32_t *);
  55 static bool edit_file_features(Elf *, int, int, char *, bool);
  56 static bool get_file_features(Elf *, int, int, uint32_t *, uint64_t *, bool);
  57 static void print_features(void);
  58 static bool print_file_features(Elf *, int, int, char *, bool);
  59 static void usage(void);
  60
  61 struct ControlFeatures {
  62         const char *alias;
  63         unsigned long value;
  64         const char *desc;
  65 };
  66
  67 static struct ControlFeatures featurelist[] = {
  68         { "noaslr",     NT_FREEBSD_FCTL_ASLR_DISABLE,   "Disable ASLR" },
  69         { "noprotmax",  NT_FREEBSD_FCTL_PROTMAX_DISABLE,
  70             "Disable implicit PROT_MAX" },
  71         { "nostackgap", NT_FREEBSD_FCTL_STKGAP_DISABLE, "Disable stack gap" },
  72         { "wxneeded",   NT_FREEBSD_FCTL_WXNEEDED, "Requires W+X mappings" },
  73         { "la48",       NT_FREEBSD_FCTL_LA48, "amd64: Limit user VA to 48bit" },
  74 };
  75
  76 static struct option long_opts[] = {
  77         { "help",       no_argument,    NULL,   'h' },
  78         { NULL,         0,              NULL,   0 }
  79 };
  80
  81 #if BYTE_ORDER == LITTLE_ENDIAN
  82 #define HOST_ENDIAN     ELFDATA2LSB
  83 #define SWAP_ENDIAN     ELFDATA2MSB
  84 #else
  85 #define HOST_ENDIAN     ELFDATA2MSB
  86 #define SWAP_ENDIAN     ELFDATA2LSB
  87 #endif
  88
  89 static bool iflag;
  90
  91 int
  92 main(int argc, char **argv)
  93 {
  94         GElf_Ehdr ehdr;
  95         Elf *elf;
  96         Elf_Kind kind;
  97         int ch, fd, retval;
  98         char *features;
  99         bool editfeatures, lflag, endian_swap;
 100
 101         lflag = 0;
 102         editfeatures = false;
 103         retval = 0;
 104         features = NULL;
 105
 106         if (elf_version(EV_CURRENT) == EV_NONE)
 107                 errx(EXIT_FAILURE, "elf_version error");
 108
 109         while ((ch = getopt_long(argc, argv, "hile:", long_opts, NULL)) != -1) {
 110                 switch (ch) {
 111                 case 'i':
 112                         iflag = true;
 113                         break;
 114                 case 'l':
 115                         print_features();
 116                         lflag = true;
 117                         break;
 118                 case 'e':
 119                         if (features != NULL)
 120                                 errx(1, "-e may be specified only once");
 121                         features = optarg;
 122                         editfeatures = true;
 123                         break;
 124                 case 'h':
 125                 default:
 126                         usage();
 127                 }
 128         }
 129         argc -= optind;
 130         argv += optind;
 131         if (argc == 0) {
 132                 if (lflag)
 133                         exit(0);
 134                 else {
 135                         warnx("no file(s) specified");
 136                         usage();
 137                 }
 138         }
 139
 140         while (argc) {
 141                 elf = NULL;
 142
 143                 if ((fd = open(argv[0],
 144                     editfeatures ? O_RDWR : O_RDONLY, 0)) < 0) {
 145                         warn("error opening file %s", argv[0]);
 146                         retval = 1;
 147                         goto fail;
 148                 }
 149
 150                 if ((elf = elf_begin(fd, ELF_C_READ, NULL)) == NULL) {
 151                         warnx("elf_begin failed: %s", elf_errmsg(-1));
 152                         retval = 1;
 153                         goto fail;
 154                 }
 155
 156                 if ((kind = elf_kind(elf)) != ELF_K_ELF) {
 157                         if (kind == ELF_K_AR)
 158                                 warnx("file '%s' is an archive", argv[0]);
 159                         else
 160                                 warnx("file '%s' is not an ELF file", argv[0]);
 161                         retval = 1;
 162                         goto fail;
 163                 }
 164
 165                 if (gelf_getehdr(elf, &ehdr) == NULL) {
 166                         warnx("gelf_getehdr: %s", elf_errmsg(-1));
 167                         retval = 1;
 168                         goto fail;
 169                 }
 170
 171                 if (ehdr.e_ident[EI_DATA] == HOST_ENDIAN) {
 172                         endian_swap = false;
 173                 } else if (ehdr.e_ident[EI_DATA] == SWAP_ENDIAN) {
 174                         endian_swap = true;
 175                 } else {
 176                         warnx("file endianness unknown");
 177                         retval = 1;
 178                         goto fail;
 179                 }
 180
 181                 if (!editfeatures) {
 182                         if (!print_file_features(elf, ehdr.e_phnum, fd,
 183                             argv[0], endian_swap)) {
 184                                 retval = 1;
 185                                 goto fail;
 186                         }
 187                 } else if (!edit_file_features(elf, ehdr.e_phnum, fd,
 188                     features, endian_swap)) {
 189                         retval = 1;
 190                         goto fail;
 191                 }
 192 fail:
 193                 if (elf != NULL)
 194                         elf_end(elf);
 195
 196                 if (fd >= 0)
 197                         close(fd);
 198
 199                 argc--;
 200                 argv++;
 201         }
 202
 203         return (retval);
 204 }
 205
 206 #define USAGE_MESSAGE \
 207         "\
 208 Usage: %s [options] file...\n\
 209   Set or display the control features for an ELF object.\n\n\
 210   Supported options are:\n\
 211   -l                        List known control features.\n\
 212   -i                        Ignore unknown features.\n\
 213   -e [+-=]feature,list      Edit features from a comma separated list.\n\
 214   -h | --help               Print a usage message and exit.\n"
 215
 216 static void
 217 usage(void)
 218 {
 219
 220         fprintf(stderr, USAGE_MESSAGE, ELFTC_GETPROGNAME());
 221         exit(1);
 222 }
 223
 224 static bool
 225 convert_to_feature_val(const char *feature_str, uint32_t *feature_val)
 226 {
 227         char *feature, *feature_tmp;
 228         int i, len;
 229         uint32_t input;
 230         char operation;
 231
 232         input = 0;
 233         operation = *feature_str;
 234         feature_str++;
 235
 236         if (operation != '+' && operation != '-' && operation != '=')
 237                 errx(1, "'%c' not an operator - use '+', '-', '='", operation);
 238
 239         if ((feature_tmp = strdup(feature_str)) == NULL)
 240                 err(1, "strdup");
 241         len = nitems(featurelist);
 242         while ((feature = strsep(&feature_tmp, ",")) != NULL) {
 243                 for (i = 0; i < len; ++i) {
 244                         if (strcmp(featurelist[i].alias, feature) == 0) {
 245                                 input |= featurelist[i].value;
 246                                 break;
 247                         }
 248                         /* XXX Backwards compatibility for "no"-prefix flags. */
 249                         if (strncmp(featurelist[i].alias, "no", 2) == 0 &&
 250                             strcmp(featurelist[i].alias + 2, feature) == 0) {
 251                                 input |= featurelist[i].value;
 252                                 warnx(
 253                                     "interpreting %s as %s; please specify %s",
 254                                     feature, featurelist[i].alias,
 255                                     featurelist[i].alias);
 256                                 break;
 257                         }
 258                 }
 259                 if (i == len) {
 260                         if (isdigit(feature[0])) {
 261                                 char *eptr;
 262                                 unsigned long long val;
 263
 264                                 errno = 0;
 265                                 val = strtoll(feature, &eptr, 0);
 266                                 if (eptr == feature || *eptr != '\0')
 267                                         errno = EINVAL;
 268                                 else if (val > UINT32_MAX)
 269                                         errno = ERANGE;
 270                                 if (errno != 0) {
 271                                         warn("%s invalid", feature);
 272                                         free(feature_tmp);
 273                                         return (false);
 274                                 }
 275                                 input |= val;
 276                         } else {
 277                                 warnx("%s is not a valid feature", feature);
 278                                 if (!iflag) {
 279                                         free(feature_tmp);
 280                                         return (false);
 281                                 }
 282                         }
 283                 }
 284         }
 285
 286         if (operation == '+') {
 287                 *feature_val |= input;
 288         } else if (operation == '=') {
 289                 *feature_val = input;
 290         } else if (operation == '-') {
 291                 *feature_val &= ~input;
 292         }
 293         free(feature_tmp);
 294         return (true);
 295 }
 296
 297 static bool
 298 edit_file_features(Elf *elf, int phcount, int fd, char *val, bool endian_swap)
 299 {
 300         uint32_t features, prev_features;
 301         uint64_t off;
 302
 303         if (!get_file_features(elf, phcount, fd, &features, &off,
 304             endian_swap)) {
 305                 warnx("NT_FREEBSD_FEATURE_CTL note not found");
 306                 return (false);
 307         }
 308
 309         prev_features = features;
 310         if (!convert_to_feature_val(val, &features))
 311                 return (false);
 312         /* Avoid touching file if no change. */
 313         if (features == prev_features)
 314                 return (true);
 315
 316         if (endian_swap)
 317                 features = bswap32(features);
 318
 319         if (lseek(fd, off, SEEK_SET) == -1 ||
 320             write(fd, &features, sizeof(features)) <
 321             (ssize_t)sizeof(features)) {
 322                 warnx("error writing feature value");
 323                 return (false);
 324         }
 325         return (true);
 326 }
 327
 328 static void
 329 print_features(void)
 330 {
 331         size_t i;
 332
 333         printf("Known features are:\n");
 334         for (i = 0; i < nitems(featurelist); ++i)
 335                 printf("%-16s%s\n", featurelist[i].alias,
 336                     featurelist[i].desc);
 337 }
 338
 339 static bool
 340 print_file_features(Elf *elf, int phcount, int fd, char *filename,
 341     bool endian_swap)
 342 {
 343         uint32_t features;
 344         unsigned long i;
 345
 346         if (!get_file_features(elf, phcount, fd, &features, NULL,
 347             endian_swap)) {
 348                 return (false);
 349         }
 350
 351         printf("File '%s' features:\n", filename);
 352         for (i = 0; i < nitems(featurelist); ++i) {
 353                 printf("%-16s'%s' is ", featurelist[i].alias,
 354                     featurelist[i].desc);
 355
 356                 if ((featurelist[i].value & features) == 0)
 357                         printf("un");
 358
 359                 printf("set.\n");
 360         }
 361         return (true);
 362 }
 363
 364 static bool
 365 get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
 366     uint64_t *off, bool endian_swap)
 367 {
 368         GElf_Phdr phdr;
 369         Elf_Note note;
 370         unsigned long read_total;
 371         int namesz, descsz, i;
 372         char *name;
 373
 374         /*
 375          * Go through each program header to find one that is of type PT_NOTE
 376          * and has a note for feature control.
 377          */
 378         for (i = 0; i < phcount; ++i) {
 379                 if (gelf_getphdr(elf, i, &phdr) == NULL) {
 380                         warnx("gelf_getphdr failed: %s", elf_errmsg(-1));
 381                         return (false);
 382                 }
 383
 384                 if (phdr.p_type != PT_NOTE)
 385                         continue;
 386
 387                 if (lseek(fd, phdr.p_offset, SEEK_SET) < 0) {
 388                         warn("lseek() failed:");
 389                         return (false);
 390                 }
 391
 392                 read_total = 0;
 393                 while (read_total < phdr.p_filesz) {
 394                         if (read(fd, &note, sizeof(note)) <
 395                             (ssize_t)sizeof(note)) {
 396                                 warnx("elf note header too short");
 397                                 return (false);
 398                         }
 399                         read_total += sizeof(note);
 400
 401                         if (endian_swap) {
 402                                 note.n_namesz = bswap32(note.n_namesz);
 403                                 note.n_descsz = bswap32(note.n_descsz);
 404                                 note.n_type = bswap32(note.n_type);
 405                         }
 406
 407                         /*
 408                          * XXX: Name and descriptor are 4 byte aligned, however,
 409                          * the size given doesn't include the padding.
 410                          */
 411                         namesz = roundup2(note.n_namesz, 4);
 412                         name = malloc(namesz);
 413                         if (name == NULL) {
 414                                 warn("malloc() failed.");
 415                                 return (false);
 416                         }
 417                         descsz = roundup2(note.n_descsz, 4);
 418                         if (read(fd, name, namesz) < namesz) {
 419                                 warnx("elf note name too short");
 420                                 free(name);
 421                                 return (false);
 422                         }
 423                         read_total += namesz;
 424
 425                         if (note.n_namesz != 8 ||
 426                             strncmp("FreeBSD", name, 7) != 0 ||
 427                             note.n_type != NT_FREEBSD_FEATURE_CTL) {
 428                                 /* Not the right note. Skip the description */
 429                                 if (lseek(fd, descsz, SEEK_CUR) < 0) {
 430                                         warn("lseek() failed.");
 431                                         free(name);
 432                                         return (false);
 433                                 }
 434                                 read_total += descsz;
 435                                 free(name);
 436                                 continue;
 437                         }
 438
 439                         if (note.n_descsz < sizeof(uint32_t)) {
 440                                 warnx("Feature descriptor can't "
 441                                     "be less than 4 bytes");
 442                                 free(name);
 443                                 return (false);
 444                         }
 445
 446                         /*
 447                          * XXX: For now we look at only 4 bytes of the
 448                          * descriptor. This should respect descsz.
 449                          */
 450                         if (note.n_descsz > sizeof(uint32_t))
 451                                 warnx("Feature note is bigger than expected");
 452                         if (read(fd, features, sizeof(uint32_t)) <
 453                             (ssize_t)sizeof(uint32_t)) {
 454                                 warnx("feature note data too short");
 455                                 free(name);
 456                                 return (false);
 457                         }
 458                         if (endian_swap)
 459                                 *features = bswap32(*features);
 460                         if (off != NULL)
 461                                 *off = phdr.p_offset + read_total;
 462                         free(name);
 463                         return (true);
 464                 }
 465         }
 466
 467         warnx("NT_FREEBSD_FEATURE_CTL note not found");
 468         return (false);
 469 }