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