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