crypto/asymmetric_keys/verify_pefile.c

   1 /* Parse a signed PE binary
   2  *
   3  * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #define pr_fmt(fmt) "PEFILE: "fmt
  13 #include <linux/module.h>
  14 #include <linux/kernel.h>
  15 #include <linux/slab.h>
  16 #include <linux/err.h>
  17 #include <linux/pe.h>
  18 #include <linux/asn1.h>
  19 #include <crypto/pkcs7.h>
  20 #include <crypto/hash.h>
  21 #include "verify_pefile.h"
  22
  23 /*
  24  * Parse a PE binary.
  25  */
  26 static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
  27                                struct pefile_context *ctx)
  28 {
  29         const struct mz_hdr *mz = pebuf;
  30         const struct pe_hdr *pe;
  31         const struct pe32_opt_hdr *pe32;
  32         const struct pe32plus_opt_hdr *pe64;
  33         const struct data_directory *ddir;
  34         const struct data_dirent *dde;
  35         const struct section_header *secs, *sec;
  36         size_t cursor, datalen = pelen;
  37
  38         kenter("");
  39
  40 #define chkaddr(base, x, s)                                             \
  41         do {                                                            \
  42                 if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
  43                         return -ELIBBAD;                                \
  44         } while (0)
  45
  46         chkaddr(0, 0, sizeof(*mz));
  47         if (mz->magic != MZ_MAGIC)
  48                 return -ELIBBAD;
  49         cursor = sizeof(*mz);
  50
  51         chkaddr(cursor, mz->peaddr, sizeof(*pe));
  52         pe = pebuf + mz->peaddr;
  53         if (pe->magic != PE_MAGIC)
  54                 return -ELIBBAD;
  55         cursor = mz->peaddr + sizeof(*pe);
  56
  57         chkaddr(0, cursor, sizeof(pe32->magic));
  58         pe32 = pebuf + cursor;
  59         pe64 = pebuf + cursor;
  60
  61         switch (pe32->magic) {
  62         case PE_OPT_MAGIC_PE32:
  63                 chkaddr(0, cursor, sizeof(*pe32));
  64                 ctx->image_checksum_offset =
  65                         (unsigned long)&pe32->csum - (unsigned long)pebuf;
  66                 ctx->header_size = pe32->header_size;
  67                 cursor += sizeof(*pe32);
  68                 ctx->n_data_dirents = pe32->data_dirs;
  69                 break;
  70
  71         case PE_OPT_MAGIC_PE32PLUS:
  72                 chkaddr(0, cursor, sizeof(*pe64));
  73                 ctx->image_checksum_offset =
  74                         (unsigned long)&pe64->csum - (unsigned long)pebuf;
  75                 ctx->header_size = pe64->header_size;
  76                 cursor += sizeof(*pe64);
  77                 ctx->n_data_dirents = pe64->data_dirs;
  78                 break;
  79
  80         default:
  81                 pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic);
  82                 return -ELIBBAD;
  83         }
  84
  85         pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
  86         pr_debug("header size = %x\n", ctx->header_size);
  87
  88         if (cursor >= ctx->header_size || ctx->header_size >= datalen)
  89                 return -ELIBBAD;
  90
  91         if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
  92                 return -ELIBBAD;
  93
  94         ddir = pebuf + cursor;
  95         cursor += sizeof(*dde) * ctx->n_data_dirents;
  96
  97         ctx->cert_dirent_offset =
  98                 (unsigned long)&ddir->certs - (unsigned long)pebuf;
  99         ctx->certs_size = ddir->certs.size;
 100
 101         if (!ddir->certs.virtual_address || !ddir->certs.size) {
 102                 pr_debug("Unsigned PE binary\n");
 103                 return -EKEYREJECTED;
 104         }
 105
 106         chkaddr(ctx->header_size, ddir->certs.virtual_address,
 107                 ddir->certs.size);
 108         ctx->sig_offset = ddir->certs.virtual_address;
 109         ctx->sig_len = ddir->certs.size;
 110         pr_debug("cert = %x @%x [%*ph]\n",
 111                  ctx->sig_len, ctx->sig_offset,
 112                  ctx->sig_len, pebuf + ctx->sig_offset);
 113
 114         ctx->n_sections = pe->sections;
 115         if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
 116                 return -ELIBBAD;
 117         ctx->secs = secs = pebuf + cursor;
 118
 119         return 0;
 120 }
 121
 122 /*
 123  * Check and strip the PE wrapper from around the signature and check that the
 124  * remnant looks something like PKCS#7.
 125  */
 126 static int pefile_strip_sig_wrapper(const void *pebuf,
 127                                     struct pefile_context *ctx)
 128 {
 129         struct win_certificate wrapper;
 130         const u8 *pkcs7;
 131
 132         if (ctx->sig_len < sizeof(wrapper)) {
 133                 pr_debug("Signature wrapper too short\n");
 134                 return -ELIBBAD;
 135         }
 136
 137         memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
 138         pr_debug("sig wrapper = { %x, %x, %x }\n",
 139                  wrapper.length, wrapper.revision, wrapper.cert_type);
 140
 141         /* Both pesign and sbsign round up the length of certificate table
 142          * (in optional header data directories) to 8 byte alignment.
 143          */
 144         if (round_up(wrapper.length, 8) != ctx->sig_len) {
 145                 pr_debug("Signature wrapper len wrong\n");
 146                 return -ELIBBAD;
 147         }
 148         if (wrapper.revision != WIN_CERT_REVISION_2_0) {
 149                 pr_debug("Signature is not revision 2.0\n");
 150                 return -ENOTSUPP;
 151         }
 152         if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
 153                 pr_debug("Signature certificate type is not PKCS\n");
 154                 return -ENOTSUPP;
 155         }
 156
 157         /* Looks like actual pkcs signature length is in wrapper->length.
 158          * size obtained from data dir entries lists the total size of
 159          * certificate table which is also aligned to octawrod boundary.
 160          *
 161          * So set signature length field appropriately.
 162          */
 163         ctx->sig_len = wrapper.length;
 164         ctx->sig_offset += sizeof(wrapper);
 165         ctx->sig_len -= sizeof(wrapper);
 166         if (ctx->sig_len == 0) {
 167                 pr_debug("Signature data missing\n");
 168                 return -EKEYREJECTED;
 169         }
 170
 171         /* What's left should a PKCS#7 cert */
 172         pkcs7 = pebuf + ctx->sig_offset;
 173         if (pkcs7[0] == (ASN1_CONS_BIT | ASN1_SEQ)) {
 174                 if (pkcs7[1] == 0x82 &&
 175                     pkcs7[2] == (((ctx->sig_len - 4) >> 8) & 0xff) &&
 176                     pkcs7[3] ==  ((ctx->sig_len - 4)       & 0xff))
 177                         return 0;
 178                 if (pkcs7[1] == 0x80)
 179                         return 0;
 180                 if (pkcs7[1] > 0x82)
 181                         return -EMSGSIZE;
 182         }
 183
 184         pr_debug("Signature data not PKCS#7\n");
 185         return -ELIBBAD;
 186 }
 187
 188 /*
 189  * Compare two sections for canonicalisation.
 190  */
 191 static int pefile_compare_shdrs(const void *a, const void *b)
 192 {
 193         const struct section_header *shdra = a;
 194         const struct section_header *shdrb = b;
 195         int rc;
 196
 197         if (shdra->data_addr > shdrb->data_addr)
 198                 return 1;
 199         if (shdrb->data_addr > shdra->data_addr)
 200                 return -1;
 201
 202         if (shdra->virtual_address > shdrb->virtual_address)
 203                 return 1;
 204         if (shdrb->virtual_address > shdra->virtual_address)
 205                 return -1;
 206
 207         rc = strcmp(shdra->name, shdrb->name);
 208         if (rc != 0)
 209                 return rc;
 210
 211         if (shdra->virtual_size > shdrb->virtual_size)
 212                 return 1;
 213         if (shdrb->virtual_size > shdra->virtual_size)
 214                 return -1;
 215
 216         if (shdra->raw_data_size > shdrb->raw_data_size)
 217                 return 1;
 218         if (shdrb->raw_data_size > shdra->raw_data_size)
 219                 return -1;
 220
 221         return 0;
 222 }
 223
 224 /*
 225  * Load the contents of the PE binary into the digest, leaving out the image
 226  * checksum and the certificate data block.
 227  */
 228 static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen,
 229                                      struct pefile_context *ctx,
 230                                      struct shash_desc *desc)
 231 {
 232         unsigned *canon, tmp, loop, i, hashed_bytes;
 233         int ret;
 234
 235         /* Digest the header and data directory, but leave out the image
 236          * checksum and the data dirent for the signature.
 237          */
 238         ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset);
 239         if (ret < 0)
 240                 return ret;
 241
 242         tmp = ctx->image_checksum_offset + sizeof(uint32_t);
 243         ret = crypto_shash_update(desc, pebuf + tmp,
 244                                   ctx->cert_dirent_offset - tmp);
 245         if (ret < 0)
 246                 return ret;
 247
 248         tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent);
 249         ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp);
 250         if (ret < 0)
 251                 return ret;
 252
 253         canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL);
 254         if (!canon)
 255                 return -ENOMEM;
 256
 257         /* We have to canonicalise the section table, so we perform an
 258          * insertion sort.
 259          */
 260         canon[0] = 0;
 261         for (loop = 1; loop < ctx->n_sections; loop++) {
 262                 for (i = 0; i < loop; i++) {
 263                         if (pefile_compare_shdrs(&ctx->secs[canon[i]],
 264                                                  &ctx->secs[loop]) > 0) {
 265                                 memmove(&canon[i + 1], &canon[i],
 266                                         (loop - i) * sizeof(canon[0]));
 267                                 break;
 268                         }
 269                 }
 270                 canon[i] = loop;
 271         }
 272
 273         hashed_bytes = ctx->header_size;
 274         for (loop = 0; loop < ctx->n_sections; loop++) {
 275                 i = canon[loop];
 276                 if (ctx->secs[i].raw_data_size == 0)
 277                         continue;
 278                 ret = crypto_shash_update(desc,
 279                                           pebuf + ctx->secs[i].data_addr,
 280                                           ctx->secs[i].raw_data_size);
 281                 if (ret < 0) {
 282                         kfree(canon);
 283                         return ret;
 284                 }
 285                 hashed_bytes += ctx->secs[i].raw_data_size;
 286         }
 287         kfree(canon);
 288
 289         if (pelen > hashed_bytes) {
 290                 tmp = hashed_bytes + ctx->certs_size;
 291                 ret = crypto_shash_update(desc,
 292                                           pebuf + hashed_bytes,
 293                                           pelen - tmp);
 294                 if (ret < 0)
 295                         return ret;
 296         }
 297
 298         return 0;
 299 }
 300
 301 /*
 302  * Digest the contents of the PE binary, leaving out the image checksum and the
 303  * certificate data block.
 304  */
 305 static int pefile_digest_pe(const void *pebuf, unsigned int pelen,
 306                             struct pefile_context *ctx)
 307 {
 308         struct crypto_shash *tfm;
 309         struct shash_desc *desc;
 310         size_t digest_size, desc_size;
 311         void *digest;
 312         int ret;
 313
 314         kenter(",%u", ctx->digest_algo);
 315
 316         /* Allocate the hashing algorithm we're going to need and find out how
 317          * big the hash operational data will be.
 318          */
 319         tfm = crypto_alloc_shash(hash_algo_name[ctx->digest_algo], 0, 0);
 320         if (IS_ERR(tfm))
 321                 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
 322
 323         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
 324         digest_size = crypto_shash_digestsize(tfm);
 325
 326         if (digest_size != ctx->digest_len) {
 327                 pr_debug("Digest size mismatch (%zx != %x)\n",
 328                          digest_size, ctx->digest_len);
 329                 ret = -EBADMSG;
 330                 goto error_no_desc;
 331         }
 332         pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size);
 333
 334         ret = -ENOMEM;
 335         desc = kzalloc(desc_size + digest_size, GFP_KERNEL);
 336         if (!desc)
 337                 goto error_no_desc;
 338
 339         desc->tfm   = tfm;
 340         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 341         ret = crypto_shash_init(desc);
 342         if (ret < 0)
 343                 goto error;
 344
 345         ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc);
 346         if (ret < 0)
 347                 goto error;
 348
 349         digest = (void *)desc + desc_size;
 350         ret = crypto_shash_final(desc, digest);
 351         if (ret < 0)
 352                 goto error;
 353
 354         pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest);
 355
 356         /* Check that the PE file digest matches that in the MSCODE part of the
 357          * PKCS#7 certificate.
 358          */
 359         if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) {
 360                 pr_debug("Digest mismatch\n");
 361                 ret = -EKEYREJECTED;
 362         } else {
 363                 pr_debug("The digests match!\n");
 364         }
 365
 366 error:
 367         kfree(desc);
 368 error_no_desc:
 369         crypto_free_shash(tfm);
 370         kleave(" = %d", ret);
 371         return ret;
 372 }
 373
 374 /**
 375  * verify_pefile_signature - Verify the signature on a PE binary image
 376  * @pebuf: Buffer containing the PE binary image
 377  * @pelen: Length of the binary image
 378  * @trust_keyring: Signing certificates to use as starting points
 379  * @_trusted: Set to true if trustworth, false otherwise
 380  *
 381  * Validate that the certificate chain inside the PKCS#7 message inside the PE
 382  * binary image intersects keys we already know and trust.
 383  *
 384  * Returns, in order of descending priority:
 385  *
 386  *  (*) -ELIBBAD if the image cannot be parsed, or:
 387  *
 388  *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
 389  *      key, or:
 390  *
 391  *  (*) 0 if at least one signature chain intersects with the keys in the trust
 392  *      keyring, or:
 393  *
 394  *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
 395  *      chain.
 396  *
 397  *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
 398  *      the message.
 399  *
 400  * May also return -ENOMEM.
 401  */
 402 int verify_pefile_signature(const void *pebuf, unsigned pelen,
 403                             struct key *trusted_keyring, bool *_trusted)
 404 {
 405         struct pkcs7_message *pkcs7;
 406         struct pefile_context ctx;
 407         const void *data;
 408         size_t datalen;
 409         int ret;
 410
 411         kenter("");
 412
 413         memset(&ctx, 0, sizeof(ctx));
 414         ret = pefile_parse_binary(pebuf, pelen, &ctx);
 415         if (ret < 0)
 416                 return ret;
 417
 418         ret = pefile_strip_sig_wrapper(pebuf, &ctx);
 419         if (ret < 0)
 420                 return ret;
 421
 422         pkcs7 = pkcs7_parse_message(pebuf + ctx.sig_offset, ctx.sig_len);
 423         if (IS_ERR(pkcs7))
 424                 return PTR_ERR(pkcs7);
 425         ctx.pkcs7 = pkcs7;
 426
 427         ret = pkcs7_get_content_data(ctx.pkcs7, &data, &datalen, false);
 428         if (ret < 0 || datalen == 0) {
 429                 pr_devel("PKCS#7 message does not contain data\n");
 430                 ret = -EBADMSG;
 431                 goto error;
 432         }
 433
 434         ret = mscode_parse(&ctx);
 435         if (ret < 0)
 436                 goto error;
 437
 438         pr_debug("Digest: %u [%*ph]\n",
 439                  ctx.digest_len, ctx.digest_len, ctx.digest);
 440
 441         /* Generate the digest and check against the PKCS7 certificate
 442          * contents.
 443          */
 444         ret = pefile_digest_pe(pebuf, pelen, &ctx);
 445         if (ret < 0)
 446                 goto error;
 447
 448         ret = pkcs7_verify(pkcs7);
 449         if (ret < 0)
 450                 goto error;
 451
 452         ret = pkcs7_validate_trust(pkcs7, trusted_keyring, _trusted);
 453
 454 error:
 455         pkcs7_free_message(ctx.pkcs7);
 456         return ret;
 457 }