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 };
  70
  71 static struct option long_opts[] = {
  72         { "help",       no_argument,    NULL,   'h' },
  73         { NULL,         0,              NULL,   0 }
  74 };
  75
  76 #if BYTE_ORDER == LITTLE_ENDIAN
  77 #define SUPPORTED_ENDIAN ELFDATA2LSB
  78 #else
  79 #define SUPPORTED_ENDIAN ELFDATA2MSB
  80 #endif
  81
  82 int
  83 main(int argc, char **argv)
  84 {
  85         GElf_Ehdr ehdr;
  86         Elf *elf;
  87         Elf_Kind kind;
  88         int ch, fd, retval;
  89         char *features;
  90         bool editfeatures, lflag;
  91
  92         lflag = 0;
  93         editfeatures = false;
  94         retval = 0;
  95         features = NULL;
  96
  97         if (elf_version(EV_CURRENT) == EV_NONE)
  98                 errx(EXIT_FAILURE, "elf_version error");
  99
 100         while ((ch = getopt_long(argc, argv, "hle:", long_opts, NULL)) != -1) {
 101                 switch (ch) {
 102                 case 'l':
 103                         print_features();
 104                         lflag = true;
 105                         break;
 106                 case 'e':
 107                         features = optarg;
 108                         editfeatures = true;
 109                         break;
 110                 case 'h':
 111                 default:
 112                         usage();
 113                 }
 114         }
 115         argc -= optind;
 116         argv += optind;
 117         if (argc == 0) {
 118                 if (lflag)
 119                         exit(0);
 120                 else {
 121                         warnx("no file(s) specified");
 122                         usage();
 123                 }
 124         }
 125
 126         while (argc) {
 127                 elf = NULL;
 128
 129                 if ((fd = open(argv[0],
 130                     editfeatures ? O_RDWR : O_RDONLY, 0)) < 0) {
 131                         warn("error opening file %s", argv[0]);
 132                         retval = 1;
 133                         goto fail;
 134                 }
 135
 136                 if ((elf = elf_begin(fd, ELF_C_READ, NULL)) == NULL) {
 137                         warnx("elf_begin failed: %s", elf_errmsg(-1));
 138                         retval = 1;
 139                         goto fail;
 140                 }
 141
 142                 if ((kind = elf_kind(elf)) != ELF_K_ELF) {
 143                         if (kind == ELF_K_AR)
 144                                 warnx("file '%s' is an archive", argv[0]);
 145                         else
 146                                 warnx("file '%s' is not an ELF file", argv[0]);
 147                         retval = 1;
 148                         goto fail;
 149                 }
 150
 151                 if (gelf_getehdr(elf, &ehdr) == NULL) {
 152                         warnx("gelf_getehdr: %s", elf_errmsg(-1));
 153                         retval = 1;
 154                         goto fail;
 155                 }
 156                 /*
 157                  * XXX need to support cross-endian operation, but for now
 158                  * exit on error rather than misbehaving.
 159                  */
 160                 if (ehdr.e_ident[EI_DATA] != SUPPORTED_ENDIAN) {
 161                         warnx("file endianness must match host");
 162                         retval = 1;
 163                         goto fail;
 164                 }
 165
 166                 if (!editfeatures) {
 167                         if (!print_file_features(elf, ehdr.e_phnum, fd,
 168                             argv[0])) {
 169                                 retval = 1;
 170                                 goto fail;
 171                         }
 172                 } else if (!edit_file_features(elf, ehdr.e_phnum, fd,
 173                     features)) {
 174                         retval = 1;
 175                         goto fail;
 176                 }
 177 fail:
 178                 if (elf != NULL)
 179                         elf_end(elf);
 180
 181                 if (fd >= 0)
 182                         close(fd);
 183
 184                 argc--;
 185                 argv++;
 186         }
 187
 188         return (retval);
 189 }
 190
 191 #define USAGE_MESSAGE \
 192         "\
 193 Usage: %s [options] file...\n\
 194   Set or display the control features for an ELF object.\n\n\
 195   Supported options are:\n\
 196   -l                        List known control features.\n\
 197   -e [+-=]feature,list      Edit features from a comma separated list.\n\
 198   -h | --help               Print a usage message and exit.\n"
 199
 200 static void
 201 usage(void)
 202 {
 203
 204         fprintf(stderr, USAGE_MESSAGE, ELFTC_GETPROGNAME());
 205         exit(1);
 206 }
 207
 208 static bool
 209 convert_to_feature_val(char *feature_str, uint32_t *feature_val)
 210 {
 211         char *feature;
 212         int i, len;
 213         uint32_t input;
 214         char operation;
 215
 216         input = 0;
 217         operation = *feature_str;
 218         feature_str++;
 219         len = nitems(featurelist);
 220         while ((feature = strsep(&feature_str, ",")) != NULL) {
 221                 for (i = 0; i < len; ++i) {
 222                         if (strcmp(featurelist[i].alias, feature) == 0) {
 223                                 input |= featurelist[i].value;
 224                                 break;
 225                         }
 226                 }
 227                 if (i == len) {
 228                         warnx("%s is not a valid feature", feature);
 229                         return (false);
 230                 }
 231         }
 232
 233         if (operation == '+') {
 234                 *feature_val |= input;
 235         } else if (operation == '=') {
 236                 *feature_val = input;
 237         } else if (operation == '-') {
 238                 *feature_val &= ~input;
 239         } else {
 240                 warnx("'%c' not an operator - use '+', '-', '='",
 241                     feature_str[0]);
 242                 return (false);
 243         }
 244         return (true);
 245 }
 246
 247 static bool
 248 edit_file_features(Elf *elf, int phcount, int fd, char *val)
 249 {
 250         uint32_t features;
 251         uint64_t off;
 252
 253         if (!get_file_features(elf, phcount, fd, &features, &off)) {
 254                 warnx("NT_FREEBSD_FEATURE_CTL note not found");
 255                 return (false);
 256         }
 257
 258         if (!convert_to_feature_val(val, &features))
 259                 return (false);
 260
 261         if (lseek(fd, off, SEEK_SET) == -1 ||
 262             write(fd, &features, sizeof(features)) <
 263             (ssize_t)sizeof(features)) {
 264                 warnx("error writing feature value");
 265                 return (false);
 266         }
 267         return (true);
 268 }
 269
 270 static void
 271 print_features(void)
 272 {
 273         size_t i;
 274
 275         printf("Known features are:\n");
 276         for (i = 0; i < nitems(featurelist); ++i)
 277                 printf("%-16s%s\n", featurelist[i].alias,
 278                     featurelist[i].desc);
 279 }
 280
 281 static bool
 282 print_file_features(Elf *elf, int phcount, int fd, char *filename)
 283 {
 284         uint32_t features;
 285         unsigned long i;
 286
 287         if (!get_file_features(elf, phcount, fd, &features, NULL)) {
 288                 return (false);
 289         }
 290
 291         printf("File '%s' features:\n", filename);
 292         for (i = 0; i < nitems(featurelist); ++i) {
 293                 printf("%-16s'%s' is ", featurelist[i].alias,
 294                     featurelist[i].desc);
 295
 296                 if ((featurelist[i].value & features) == 0)
 297                         printf("un");
 298
 299                 printf("set.\n");
 300         }
 301         return (true);
 302 }
 303
 304 static bool
 305 get_file_features(Elf *elf, int phcount, int fd, uint32_t *features,
 306     uint64_t *off)
 307 {
 308         GElf_Phdr phdr;
 309         Elf_Note note;
 310         unsigned long read_total;
 311         int namesz, descsz, i;
 312         char *name;
 313         ssize_t size;
 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                         size = read(fd, &note, sizeof(note));
 336                         if (size < (ssize_t)sizeof(note)) {
 337                                 warn("read() failed:");
 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                         size = read(fd, name, namesz);
 354                         read_total += namesz;
 355
 356                         if (note.n_namesz != 8 ||
 357                             strncmp("FreeBSD", name, 7) != 0 ||
 358                             note.n_type != NT_FREEBSD_FEATURE_CTL) {
 359                                 /* Not the right note. Skip the description */
 360                                 if (lseek(fd, descsz, SEEK_CUR) < 0) {
 361                                         warn("lseek() failed.");
 362                                         free(name);
 363                                         return (false);
 364                                 }
 365                                 read_total += descsz;
 366                                 free(name);
 367                                 continue;
 368                         }
 369
 370                         if (note.n_descsz < sizeof(uint32_t)) {
 371                                 warnx("Feature descriptor can't "
 372                                     "be less than 4 bytes");
 373                                 free(name);
 374                                 return (false);
 375                         }
 376
 377                         /*
 378                          * XXX: For now we look at only 4 bytes of the
 379                          *      descriptor. This should respect descsz.
 380                          */
 381                         if (note.n_descsz > sizeof(uint32_t))
 382                                 warnx("Feature note is bigger than expected");
 383                         read(fd, features, sizeof(uint32_t));
 384                         if (off != NULL)
 385                                 *off = phdr.p_offset + read_total;
 386                         free(name);
 387                         return (true);
 388                 }
 389         }
 390
 391         warnx("NT_FREEBSD_FEATURE_CTL note not found");
 392         return (false);
 393 }