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