usr.bin/elfctl/elfctl.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   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(char *, uint32_t *);
  55 static bool edit_file_features(Elf *, int, int, char *);
  56 static bool get_file_features(Elf *, int, int, uint32_t *, uint64_t *);
  57 static void print_features(void);
  58 static bool print_file_features(Elf *, int, int, char *);
  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         { "aslr",       NT_FREEBSD_FCTL_ASLR_DISABLE,   "Disable ASLR" },
  69         { "protmax",    NT_FREEBSD_FCTL_PROTMAX_DISABLE,
  70             "Disable implicit PROT_MAX" },
  71         { "stackgap",   NT_FREEBSD_FCTL_STKGAP_DISABLE, "Disable stack gap" },
  72         { "wxneeded",   NT_FREEBSD_FCTL_WXNEEDED, "Requires W+X mappings" },
  73 #ifdef NT_FREEBSD_FCTL_LA48
  74         { "la48",       NT_FREEBSD_FCTL_LA48, "amd64: Limit user VA to 48bit" },
  75 #endif
  76         { "aslrstkgap", NT_FREEBSD_FCTL_ASG_DISABLE, "Disable ASLR stack gap" },
  77 };
  78
  79 static struct option long_opts[] = {
  80         { "help",       no_argument,    NULL,   'h' },
  81         { NULL,         0,              NULL,   0 }
  82 };
  83
  84 #if BYTE_ORDER == LITTLE_ENDIAN
  85 #define SUPPORTED_ENDIAN ELFDATA2LSB
  86 #else
  87 #define SUPPORTED_ENDIAN ELFDATA2MSB
  88 #endif
  89
  90 static bool iflag;
  91
  92 int
  93 main(int argc, char **argv)
  94 {
  95         GElf_Ehdr ehdr;
  96         Elf *elf;
  97         Elf_Kind kind;
  98         int ch, fd, retval;
  99         char *features;
 100         bool editfeatures, lflag;
 101
 102         lflag = 0;
 103         editfeatures = false;
 104         retval = 0;
 105         features = NULL;
 106
 107         if (elf_version(EV_CURRENT) == EV_NONE)
 108                 errx(EXIT_FAILURE, "elf_version error");
 109
 110         while ((ch = getopt_long(argc, argv, "hile:", long_opts, NULL)) != -1) {
 111                 switch (ch) {
 112                 case 'i':
 113                         iflag = true;
 114                         break;
 115                 case 'l':
 116                         print_features();
 117                         lflag = true;
 118                         break;
 119                 case 'e':
 120                         features = optarg;
 121                         editfeatures = true;
 122                         break;
 123                 case 'h':
 124                 default:
 125                         usage();
 126                 }
 127         }
 128         argc -= optind;
 129         argv += optind;
 130         if (argc == 0) {
 131                 if (lflag)
 132                         exit(0);
 133                 else {
 134                         warnx("no file(s) specified");
 135                         usage();
 136                 }
 137         }
 138
 139         while (argc) {
 140                 elf = NULL;
 141
 142                 if ((fd = open(argv[0],
 143                     editfeatures ? O_RDWR : O_RDONLY, 0)) < 0) {
 144                         warn("error opening file %s", argv[0]);
 145                         retval = 1;
 146                         goto fail;
 147                 }
 148
 149                 if ((elf = elf_begin(fd, ELF_C_READ, NULL)) == NULL) {
 150                         warnx("elf_begin failed: %s", elf_errmsg(-1));
 151                         retval = 1;
 152                         goto fail;
 153                 }
 154
 155                 if ((kind = elf_kind(elf)) != ELF_K_ELF) {
 156                         if (kind == ELF_K_AR)
 157                                 warnx("file '%s' is an archive", argv[0]);
 158                         else
 159                                 warnx("file '%s' is not an ELF file", argv[0]);
 160                         retval = 1;
 161                         goto fail;
 162                 }
 163
 164                 if (gelf_getehdr(elf, &ehdr) == NULL) {
 165                         warnx("gelf_getehdr: %s", elf_errmsg(-1));
 166                         retval = 1;
 167                         goto fail;
 168                 }
 169                 /*
 170                  * XXX need to support cross-endian operation, but for now
 171                  * exit on error rather than misbehaving.
 172                  */
 173                 if (ehdr.e_ident[EI_DATA] != SUPPORTED_ENDIAN) {
 174                         warnx("file endianness must match host");
 175                         retval = 1;
 176                         goto fail;
 177                 }
 178
 179                 if (!editfeatures) {
 180                         if (!print_file_features(elf, ehdr.e_phnum, fd,
 181                             argv[0])) {
 182                                 retval = 1;
 183                                 goto fail;
 184                         }
 185                 } else if (!edit_file_features(elf, ehdr.e_phnum, fd,
 186                     features)) {
 187                         retval = 1;
 188                         goto fail;
 189                 }
 190 fail:
 191                 if (elf != NULL)
 192                         elf_end(elf);
 193
 194                 if (fd >= 0)
 195                         close(fd);
 196
 197                 argc--;
 198                 argv++;
 199         }
 200
 201         return (retval);
 202 }
 203
 204 #define USAGE_MESSAGE \
 205         "\
 206 Usage: %s [options] file...\n\
 207   Set or display the control features for an ELF object.\n\n\
 208   Supported options are:\n\
 209   -l                        List known control features.\n\
 210   -i                        Ignore unknown features.\n\
 211   -e [+-=]feature,list      Edit features from a comma separated list.\n\
 212   -h | --help               Print a usage message and exit.\n"
 213
 214 static void
 215 usage(void)
 216 {
 217
 218         fprintf(stderr, USAGE_MESSAGE, ELFTC_GETPROGNAME());
 219         exit(1);
 220 }
 221
 222 static bool
 223 convert_to_feature_val(char *feature_str, uint32_t *feature_val)
 224 {
 225         char *feature;
 226         int i, len;
 227         uint32_t input;
 228         char operation;
 229
 230         input = 0;
 231         operation = *feature_str;
 232         feature_str++;
 233         len = nitems(featurelist);
 234         while ((feature = strsep(&feature_str, ",")) != NULL) {
 235                 for (i = 0; i < len; ++i) {
 236                         if (strcmp(featurelist[i].alias, feature) == 0) {
 237                                 input |= featurelist[i].value;
 238                                 break;
 239                         }
 240                         /* XXX Backwards compatibility for "no"-prefix flags. */
 241                         if (strncmp(featurelist[i].alias, "no", 2) == 0 &&
 242                             strcmp(featurelist[i].alias + 2, feature) == 0) {
 243                                 input |= featurelist[i].value;
 244                                 warnx(
 245                                     "interpreting %s as %s; please specify %s",
 246                                     feature, featurelist[i].alias,
 247                                     featurelist[i].alias);
 248                                 break;
 249                         }
 250                 }
 251                 if (i == len) {
 252                         if (isdigit(feature[0])) {
 253                                 char *eptr;
 254                                 unsigned long long val;
 255
 256                                 errno = 0;
 257                                 val = strtoll(feature, &eptr, 0);
 258                                 if (eptr == feature || *eptr != '\0')
 259                                         errno = EINVAL;
 260                                 else if (val > UINT32_MAX)
 261                                         errno = ERANGE;
 262                                 if (errno != 0) {
 263                                         warn("%s invalid", feature);
 264                                         return (false);
 265                                 }
 266                                 input |= val;
 267                         } else {
 268                                 warnx("%s is not a valid feature", feature);
 269                                 if (!iflag)
 270                                         return (false);
 271                         }
 272                 }
 273         }
 274
 275         if (operation == '+') {
 276                 *feature_val |= input;
 277         } else if (operation == '=') {
 278                 *feature_val = input;
 279         } else if (operation == '-') {
 280                 *feature_val &= ~input;
 281         } else {
 282                 warnx("'%c' not an operator - use '+', '-', '='",
 283                     feature_str[0]);
 284                 return (false);
 285         }
 286         return (true);
 287 }
 288
 289 static bool
 290 edit_file_features(Elf *elf, int phcount, int fd, char *val)
 291 {
 292         uint32_t features;
 293         uint64_t off;
 294
 295         if (!get_file_features(elf, phcount, fd, &features, &off)) {
 296                 warnx("NT_FREEBSD_FEATURE_CTL note not found");
 297                 return (false);
 298         }
 299
 300         if (!convert_to_feature_val(val, &features))
 301                 return (false);
 302
 303         if (lseek(fd, off, SEEK_SET) == -1 ||
 304             write(fd, &features, sizeof(features)) <
 305             (ssize_t)sizeof(features)) {
 306                 warnx("error writing feature value");
 307                 return (false);
 308         }
 309         return (true);
 310 }
 311
 312 static void
 313 print_features(void)
 314 {
 315         size_t i;
 316
 317         printf("Known features are:\n");
 318         for (i = 0; i < nitems(featurelist); ++i)
 319                 printf("%-16s%s\n", featurelist[i].alias,
 320                     featurelist[i].desc);
 321 }
 322
 323 static bool
 324 print_file_features(Elf *elf, int phcount, int fd, char *filename)
 325 {
 326         uint32_t features;
 327         unsigned long i;
 328
 329         if (!get_file_features(elf, phcount, fd, &features, NULL)) {
 330                 return (false);
 331         }
 332
 333         printf("File '%s' features:\n", filename);
 334         for (i = 0; i < nitems(featurelist); ++i) {
 335                 printf("%-16s'%s' is ", featurelist[i].alias,
 336                     featurelist[i].desc);
 337
 338                 if ((featurelist[i].value & features) == 0)
 339                         printf("un");
 340
 341                 printf("set.\n");
 342         }
 343         return (true);
 344 }
 345
 346 static bool
 347 get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
 348     uint64_t *off)
 349 {
 350         GElf_Phdr phdr;
 351         Elf_Note note;
 352         unsigned long read_total;
 353         int namesz, descsz, i;
 354         char *name;
 355
 356         /*
 357          * Go through each program header to find one that is of type PT_NOTE
 358          * and has a note for feature control.
 359          */
 360         for (i = 0; i < phcount; ++i) {
 361                 if (gelf_getphdr(elf, i, &phdr) == NULL) {
 362                         warnx("gelf_getphdr failed: %s", elf_errmsg(-1));
 363                         return (false);
 364                 }
 365
 366                 if (phdr.p_type != PT_NOTE)
 367                         continue;
 368
 369                 if (lseek(fd, phdr.p_offset, SEEK_SET) < 0) {
 370                         warn("lseek() failed:");
 371                         return (false);
 372                 }
 373
 374                 read_total = 0;
 375                 while (read_total < phdr.p_filesz) {
 376                         if (read(fd, &note, sizeof(note)) <
 377                             (ssize_t)sizeof(note)) {
 378                                 warnx("elf note header too short");
 379                                 return (false);
 380                         }
 381                         read_total += sizeof(note);
 382
 383                         /*
 384                          * XXX: Name and descriptor are 4 byte aligned, however,
 385                          *      the size given doesn't include the padding.
 386                          */
 387                         namesz = roundup2(note.n_namesz, 4);
 388                         name = malloc(namesz);
 389                         if (name == NULL) {
 390                                 warn("malloc() failed.");
 391                                 return (false);
 392                         }
 393                         descsz = roundup2(note.n_descsz, 4);
 394                         if (read(fd, name, namesz) < namesz) {
 395                                 warnx("elf note name too short");
 396                                 free(name);
 397                                 return (false);
 398                         }
 399                         read_total += namesz;
 400
 401                         if (note.n_namesz != 8 ||
 402                             strncmp("FreeBSD", name, 7) != 0 ||
 403                             note.n_type != NT_FREEBSD_FEATURE_CTL) {
 404                                 /* Not the right note. Skip the description */
 405                                 if (lseek(fd, descsz, SEEK_CUR) < 0) {
 406                                         warn("lseek() failed.");
 407                                         free(name);
 408                                         return (false);
 409                                 }
 410                                 read_total += descsz;
 411                                 free(name);
 412                                 continue;
 413                         }
 414
 415                         if (note.n_descsz < sizeof(uint32_t)) {
 416                                 warnx("Feature descriptor can't "
 417                                     "be less than 4 bytes");
 418                                 free(name);
 419                                 return (false);
 420                         }
 421
 422                         /*
 423                          * XXX: For now we look at only 4 bytes of the
 424                          *      descriptor. This should respect descsz.
 425                          */
 426                         if (note.n_descsz > sizeof(uint32_t))
 427                                 warnx("Feature note is bigger than expected");
 428                         if (read(fd, features, sizeof(uint32_t)) <
 429                             (ssize_t)sizeof(uint32_t)) {
 430                                 warnx("feature note data too short");
 431                                 free(name);
 432                                 return (false);
 433                         }
 434                         if (off != NULL)
 435                                 *off = phdr.p_offset + read_total;
 436                         free(name);
 437                         return (true);
 438                 }
 439         }
 440
 441         warnx("NT_FREEBSD_FEATURE_CTL note not found");
 442         return (false);
 443 }