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 <err.h>
  37 #include <fcntl.h>
  38 #include <gelf.h>
  39 #include <getopt.h>
  40 #include <libelf.h>
  41 #include <stdbool.h>
  42 #include <stdio.h>
  43 #include <stdlib.h>
  44 #include <string.h>
  45 #include <unistd.h>
  46
  47 #include "_elftc.h"
  48
  49 __FBSDID("$FreeBSD$");
  50
  51 static bool convert_to_feature_val(char *, uint32_t *);
  52 static bool edit_file_features(Elf *, int, int, char *);
  53 static bool get_file_features(Elf *, int, int, uint32_t *, uint64_t *);
  54 static void print_features(void);
  55 static bool print_file_features(Elf *, int, int, char *);
  56 static void usage(void);
  57
  58 struct ControlFeatures {
  59         const char *alias;
  60         unsigned long value;
  61         const char *desc;
  62 };
  63
  64 static struct ControlFeatures featurelist[] = {
  65         { "aslr",       NT_FREEBSD_FCTL_ASLR_DISABLE,   "Disable ASLR" },
  66         { "protmax",    NT_FREEBSD_FCTL_PROTMAX_DISABLE,
  67             "Disable implicit PROT_MAX" },
  68         { "stackgap",   NT_FREEBSD_FCTL_STKGAP_DISABLE, "Disable stack gap" },
  69         { "wxneeded",   NT_FREEBSD_FCTL_WXNEEDED, "Requires W+X mappings" },
  70 };
  71
  72 static struct option long_opts[] = {
  73         { "help",       no_argument,    NULL,   'h' },
  74         { NULL,         0,              NULL,   0 }
  75 };
  76
  77 #if BYTE_ORDER == LITTLE_ENDIAN
  78 #define SUPPORTED_ENDIAN ELFDATA2LSB
  79 #else
  80 #define SUPPORTED_ENDIAN ELFDATA2MSB
  81 #endif
  82
  83 int
  84 main(int argc, char **argv)
  85 {
  86         GElf_Ehdr ehdr;
  87         Elf *elf;
  88         Elf_Kind kind;
  89         int ch, fd, retval;
  90         char *features;
  91         bool editfeatures, lflag;
  92
  93         lflag = 0;
  94         editfeatures = false;
  95         retval = 0;
  96         features = NULL;
  97
  98         if (elf_version(EV_CURRENT) == EV_NONE)
  99                 errx(EXIT_FAILURE, "elf_version error");
 100
 101         while ((ch = getopt_long(argc, argv, "hle:", long_opts, NULL)) != -1) {
 102                 switch (ch) {
 103                 case 'l':
 104                         print_features();
 105                         lflag = true;
 106                         break;
 107                 case 'e':
 108                         features = optarg;
 109                         editfeatures = true;
 110                         break;
 111                 case 'h':
 112                 default:
 113                         usage();
 114                 }
 115         }
 116         argc -= optind;
 117         argv += optind;
 118         if (argc == 0) {
 119                 if (lflag)
 120                         exit(0);
 121                 else {
 122                         warnx("no file(s) specified");
 123                         usage();
 124                 }
 125         }
 126
 127         while (argc) {
 128                 elf = NULL;
 129
 130                 if ((fd = open(argv[0],
 131                     editfeatures ? O_RDWR : O_RDONLY, 0)) < 0) {
 132                         warn("error opening file %s", argv[0]);
 133                         retval = 1;
 134                         goto fail;
 135                 }
 136
 137                 if ((elf = elf_begin(fd, ELF_C_READ, NULL)) == NULL) {
 138                         warnx("elf_begin failed: %s", elf_errmsg(-1));
 139                         retval = 1;
 140                         goto fail;
 141                 }
 142
 143                 if ((kind = elf_kind(elf)) != ELF_K_ELF) {
 144                         if (kind == ELF_K_AR)
 145                                 warnx("file '%s' is an archive", argv[0]);
 146                         else
 147                                 warnx("file '%s' is not an ELF file", argv[0]);
 148                         retval = 1;
 149                         goto fail;
 150                 }
 151
 152                 if (gelf_getehdr(elf, &ehdr) == NULL) {
 153                         warnx("gelf_getehdr: %s", elf_errmsg(-1));
 154                         retval = 1;
 155                         goto fail;
 156                 }
 157                 /*
 158                  * XXX need to support cross-endian operation, but for now
 159                  * exit on error rather than misbehaving.
 160                  */
 161                 if (ehdr.e_ident[EI_DATA] != SUPPORTED_ENDIAN) {
 162                         warnx("file endianness must match host");
 163                         retval = 1;
 164                         goto fail;
 165                 }
 166
 167                 if (!editfeatures) {
 168                         if (!print_file_features(elf, ehdr.e_phnum, fd,
 169                             argv[0])) {
 170                                 retval = 1;
 171                                 goto fail;
 172                         }
 173                 } else if (!edit_file_features(elf, ehdr.e_phnum, fd,
 174                     features)) {
 175                         retval = 1;
 176                         goto fail;
 177                 }
 178 fail:
 179                 if (elf != NULL)
 180                         elf_end(elf);
 181
 182                 if (fd >= 0)
 183                         close(fd);
 184
 185                 argc--;
 186                 argv++;
 187         }
 188
 189         return (retval);
 190 }
 191
 192 #define USAGE_MESSAGE \
 193         "\
 194 Usage: %s [options] file...\n\
 195   Set or display the control features for an ELF object.\n\n\
 196   Supported options are:\n\
 197   -l                        List known control features.\n\
 198   -e [+-=]feature,list      Edit features from a comma separated list.\n\
 199   -h | --help               Print a usage message and exit.\n"
 200
 201 static void
 202 usage(void)
 203 {
 204
 205         fprintf(stderr, USAGE_MESSAGE, ELFTC_GETPROGNAME());
 206         exit(1);
 207 }
 208
 209 static bool
 210 convert_to_feature_val(char *feature_str, uint32_t *feature_val)
 211 {
 212         char *feature;
 213         int i, len;
 214         uint32_t input;
 215         char operation;
 216
 217         input = 0;
 218         operation = *feature_str;
 219         feature_str++;
 220         len = nitems(featurelist);
 221         while ((feature = strsep(&feature_str, ",")) != NULL) {
 222                 for (i = 0; i < len; ++i) {
 223                         if (strcmp(featurelist[i].alias, feature) == 0) {
 224                                 input |= featurelist[i].value;
 225                                 break;
 226                         }
 227                 }
 228                 if (i == len) {
 229                         warnx("%s is not a valid feature", feature);
 230                         return (false);
 231                 }
 232         }
 233
 234         if (operation == '+') {
 235                 *feature_val |= input;
 236         } else if (operation == '=') {
 237                 *feature_val = input;
 238         } else if (operation == '-') {
 239                 *feature_val &= ~input;
 240         } else {
 241                 warnx("'%c' not an operator - use '+', '-', '='",
 242                     feature_str[0]);
 243                 return (false);
 244         }
 245         return (true);
 246 }
 247
 248 static bool
 249 edit_file_features(Elf *elf, int phcount, int fd, char *val)
 250 {
 251         uint32_t features;
 252         uint64_t off;
 253
 254         if (!get_file_features(elf, phcount, fd, &features, &off)) {
 255                 warnx("NT_FREEBSD_FEATURE_CTL note not found");
 256                 return (false);
 257         }
 258
 259         if (!convert_to_feature_val(val, &features))
 260                 return (false);
 261
 262         if (lseek(fd, off, SEEK_SET) == -1 ||
 263             write(fd, &features, sizeof(features)) <
 264             (ssize_t)sizeof(features)) {
 265                 warnx("error writing feature value");
 266                 return (false);
 267         }
 268         return (true);
 269 }
 270
 271 static void
 272 print_features(void)
 273 {
 274         size_t i;
 275
 276         printf("Known features are:\n");
 277         for (i = 0; i < nitems(featurelist); ++i)
 278                 printf("%-16s%s\n", featurelist[i].alias,
 279                     featurelist[i].desc);
 280 }
 281
 282 static bool
 283 print_file_features(Elf *elf, int phcount, int fd, char *filename)
 284 {
 285         uint32_t features;
 286         unsigned long i;
 287
 288         if (!get_file_features(elf, phcount, fd, &features, NULL)) {
 289                 return (false);
 290         }
 291
 292         printf("File '%s' features:\n", filename);
 293         for (i = 0; i < nitems(featurelist); ++i) {
 294                 printf("%-16s'%s' is ", featurelist[i].alias,
 295                     featurelist[i].desc);
 296
 297                 if ((featurelist[i].value & features) == 0)
 298                         printf("un");
 299
 300                 printf("set.\n");
 301         }
 302         return (true);
 303 }
 304
 305 static bool
 306 get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
 307     uint64_t *off)
 308 {
 309         GElf_Phdr phdr;
 310         Elf_Note note;
 311         unsigned long read_total;
 312         int namesz, descsz, i;
 313         char *name;
 314
 315         /*
 316          * Go through each program header to find one that is of type PT_NOTE
 317          * and has a note for feature control.
 318          */
 319         for (i = 0; i < phcount; ++i) {
 320                 if (gelf_getphdr(elf, i, &phdr) == NULL) {
 321                         warnx("gelf_getphdr failed: %s", elf_errmsg(-1));
 322                         return (false);
 323                 }
 324
 325                 if (phdr.p_type != PT_NOTE)
 326                         continue;
 327
 328                 if (lseek(fd, phdr.p_offset, SEEK_SET) < 0) {
 329                         warn("lseek() failed:");
 330                         return (false);
 331                 }
 332
 333                 read_total = 0;
 334                 while (read_total < phdr.p_filesz) {
 335                         if (read(fd, &note, sizeof(note)) <
 336                             (ssize_t)sizeof(note)) {
 337                                 warnx("elf note header too short");
 338                                 return (false);
 339                         }
 340                         read_total += sizeof(note);
 341
 342                         /*
 343                          * XXX: Name and descriptor are 4 byte aligned, however,
 344                          *      the size given doesn't include the padding.
 345                          */
 346                         namesz = roundup2(note.n_namesz, 4);
 347                         name = malloc(namesz);
 348                         if (name == NULL) {
 349                                 warn("malloc() failed.");
 350                                 return (false);
 351                         }
 352                         descsz = roundup2(note.n_descsz, 4);
 353                         if (read(fd, name, namesz) < namesz) {
 354                                 warnx("elf note name too short");
 355                                 free(name);
 356                                 return (false);
 357                         }
 358                         read_total += namesz;
 359
 360                         if (note.n_namesz != 8 ||
 361                             strncmp("FreeBSD", name, 7) != 0 ||
 362                             note.n_type != NT_FREEBSD_FEATURE_CTL) {
 363                                 /* Not the right note. Skip the description */
 364                                 if (lseek(fd, descsz, SEEK_CUR) < 0) {
 365                                         warn("lseek() failed.");
 366                                         free(name);
 367                                         return (false);
 368                                 }
 369                                 read_total += descsz;
 370                                 free(name);
 371                                 continue;
 372                         }
 373
 374                         if (note.n_descsz < sizeof(uint32_t)) {
 375                                 warnx("Feature descriptor can't "
 376                                     "be less than 4 bytes");
 377                                 free(name);
 378                                 return (false);
 379                         }
 380
 381                         /*
 382                          * XXX: For now we look at only 4 bytes of the
 383                          *      descriptor. This should respect descsz.
 384                          */
 385                         if (note.n_descsz > sizeof(uint32_t))
 386                                 warnx("Feature note is bigger than expected");
 387                         if (read(fd, features, sizeof(uint32_t)) <
 388                             (ssize_t)sizeof(uint32_t)) {
 389                                 warnx("feature note data too short");
 390                                 free(name);
 391                                 return (false);
 392                         }
 393                         if (off != NULL)
 394                                 *off = phdr.p_offset + read_total;
 395                         free(name);
 396                         return (true);
 397                 }
 398         }
 399
 400         warnx("NT_FREEBSD_FEATURE_CTL note not found");
 401         return (false);
 402 }