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26d1164b DH |
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> | |
09dacbbd | 18 | #include <linux/asn1.h> |
e68503bd | 19 | #include <linux/verification.h> |
26d1164b DH |
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 | ||
09dacbbd DH |
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; | |
0aa04094 | 131 | unsigned len; |
09dacbbd DH |
132 | |
133 | if (ctx->sig_len < sizeof(wrapper)) { | |
134 | pr_debug("Signature wrapper too short\n"); | |
135 | return -ELIBBAD; | |
136 | } | |
137 | ||
138 | memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper)); | |
139 | pr_debug("sig wrapper = { %x, %x, %x }\n", | |
140 | wrapper.length, wrapper.revision, wrapper.cert_type); | |
141 | ||
142 | /* Both pesign and sbsign round up the length of certificate table | |
143 | * (in optional header data directories) to 8 byte alignment. | |
144 | */ | |
145 | if (round_up(wrapper.length, 8) != ctx->sig_len) { | |
146 | pr_debug("Signature wrapper len wrong\n"); | |
147 | return -ELIBBAD; | |
148 | } | |
149 | if (wrapper.revision != WIN_CERT_REVISION_2_0) { | |
150 | pr_debug("Signature is not revision 2.0\n"); | |
151 | return -ENOTSUPP; | |
152 | } | |
153 | if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) { | |
154 | pr_debug("Signature certificate type is not PKCS\n"); | |
155 | return -ENOTSUPP; | |
156 | } | |
157 | ||
0aa04094 DH |
158 | /* It looks like the pkcs signature length in wrapper->length and the |
159 | * size obtained from the data dir entries, which lists the total size | |
160 | * of certificate table, are both aligned to an octaword boundary, so | |
161 | * we may have to deal with some padding. | |
09dacbbd DH |
162 | */ |
163 | ctx->sig_len = wrapper.length; | |
164 | ctx->sig_offset += sizeof(wrapper); | |
165 | ctx->sig_len -= sizeof(wrapper); | |
0aa04094 | 166 | if (ctx->sig_len < 4) { |
09dacbbd DH |
167 | pr_debug("Signature data missing\n"); |
168 | return -EKEYREJECTED; | |
169 | } | |
170 | ||
0aa04094 | 171 | /* What's left should be a PKCS#7 cert */ |
09dacbbd | 172 | pkcs7 = pebuf + ctx->sig_offset; |
0aa04094 DH |
173 | if (pkcs7[0] != (ASN1_CONS_BIT | ASN1_SEQ)) |
174 | goto not_pkcs7; | |
175 | ||
176 | switch (pkcs7[1]) { | |
177 | case 0 ... 0x7f: | |
178 | len = pkcs7[1] + 2; | |
179 | goto check_len; | |
180 | case ASN1_INDEFINITE_LENGTH: | |
181 | return 0; | |
182 | case 0x81: | |
183 | len = pkcs7[2] + 3; | |
184 | goto check_len; | |
185 | case 0x82: | |
186 | len = ((pkcs7[2] << 8) | pkcs7[3]) + 4; | |
187 | goto check_len; | |
188 | case 0x83 ... 0xff: | |
189 | return -EMSGSIZE; | |
190 | default: | |
191 | goto not_pkcs7; | |
09dacbbd DH |
192 | } |
193 | ||
0aa04094 DH |
194 | check_len: |
195 | if (len <= ctx->sig_len) { | |
196 | /* There may be padding */ | |
197 | ctx->sig_len = len; | |
198 | return 0; | |
199 | } | |
200 | not_pkcs7: | |
09dacbbd DH |
201 | pr_debug("Signature data not PKCS#7\n"); |
202 | return -ELIBBAD; | |
203 | } | |
204 | ||
af316fc4 DH |
205 | /* |
206 | * Compare two sections for canonicalisation. | |
207 | */ | |
208 | static int pefile_compare_shdrs(const void *a, const void *b) | |
209 | { | |
210 | const struct section_header *shdra = a; | |
211 | const struct section_header *shdrb = b; | |
212 | int rc; | |
213 | ||
214 | if (shdra->data_addr > shdrb->data_addr) | |
215 | return 1; | |
216 | if (shdrb->data_addr > shdra->data_addr) | |
217 | return -1; | |
218 | ||
219 | if (shdra->virtual_address > shdrb->virtual_address) | |
220 | return 1; | |
221 | if (shdrb->virtual_address > shdra->virtual_address) | |
222 | return -1; | |
223 | ||
224 | rc = strcmp(shdra->name, shdrb->name); | |
225 | if (rc != 0) | |
226 | return rc; | |
227 | ||
228 | if (shdra->virtual_size > shdrb->virtual_size) | |
229 | return 1; | |
230 | if (shdrb->virtual_size > shdra->virtual_size) | |
231 | return -1; | |
232 | ||
233 | if (shdra->raw_data_size > shdrb->raw_data_size) | |
234 | return 1; | |
235 | if (shdrb->raw_data_size > shdra->raw_data_size) | |
236 | return -1; | |
237 | ||
238 | return 0; | |
239 | } | |
240 | ||
241 | /* | |
242 | * Load the contents of the PE binary into the digest, leaving out the image | |
243 | * checksum and the certificate data block. | |
244 | */ | |
245 | static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen, | |
246 | struct pefile_context *ctx, | |
247 | struct shash_desc *desc) | |
248 | { | |
249 | unsigned *canon, tmp, loop, i, hashed_bytes; | |
250 | int ret; | |
251 | ||
252 | /* Digest the header and data directory, but leave out the image | |
253 | * checksum and the data dirent for the signature. | |
254 | */ | |
255 | ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset); | |
256 | if (ret < 0) | |
257 | return ret; | |
258 | ||
259 | tmp = ctx->image_checksum_offset + sizeof(uint32_t); | |
260 | ret = crypto_shash_update(desc, pebuf + tmp, | |
261 | ctx->cert_dirent_offset - tmp); | |
262 | if (ret < 0) | |
263 | return ret; | |
264 | ||
265 | tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent); | |
266 | ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp); | |
267 | if (ret < 0) | |
268 | return ret; | |
269 | ||
270 | canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL); | |
271 | if (!canon) | |
272 | return -ENOMEM; | |
273 | ||
274 | /* We have to canonicalise the section table, so we perform an | |
275 | * insertion sort. | |
276 | */ | |
277 | canon[0] = 0; | |
278 | for (loop = 1; loop < ctx->n_sections; loop++) { | |
279 | for (i = 0; i < loop; i++) { | |
280 | if (pefile_compare_shdrs(&ctx->secs[canon[i]], | |
281 | &ctx->secs[loop]) > 0) { | |
282 | memmove(&canon[i + 1], &canon[i], | |
283 | (loop - i) * sizeof(canon[0])); | |
284 | break; | |
285 | } | |
286 | } | |
287 | canon[i] = loop; | |
288 | } | |
289 | ||
290 | hashed_bytes = ctx->header_size; | |
291 | for (loop = 0; loop < ctx->n_sections; loop++) { | |
292 | i = canon[loop]; | |
293 | if (ctx->secs[i].raw_data_size == 0) | |
294 | continue; | |
295 | ret = crypto_shash_update(desc, | |
296 | pebuf + ctx->secs[i].data_addr, | |
297 | ctx->secs[i].raw_data_size); | |
298 | if (ret < 0) { | |
299 | kfree(canon); | |
300 | return ret; | |
301 | } | |
302 | hashed_bytes += ctx->secs[i].raw_data_size; | |
303 | } | |
304 | kfree(canon); | |
305 | ||
306 | if (pelen > hashed_bytes) { | |
307 | tmp = hashed_bytes + ctx->certs_size; | |
308 | ret = crypto_shash_update(desc, | |
309 | pebuf + hashed_bytes, | |
310 | pelen - tmp); | |
311 | if (ret < 0) | |
312 | return ret; | |
313 | } | |
314 | ||
315 | return 0; | |
316 | } | |
317 | ||
318 | /* | |
319 | * Digest the contents of the PE binary, leaving out the image checksum and the | |
320 | * certificate data block. | |
321 | */ | |
322 | static int pefile_digest_pe(const void *pebuf, unsigned int pelen, | |
323 | struct pefile_context *ctx) | |
324 | { | |
325 | struct crypto_shash *tfm; | |
326 | struct shash_desc *desc; | |
327 | size_t digest_size, desc_size; | |
328 | void *digest; | |
329 | int ret; | |
330 | ||
4e8ae72a | 331 | kenter(",%s", ctx->digest_algo); |
af316fc4 DH |
332 | |
333 | /* Allocate the hashing algorithm we're going to need and find out how | |
334 | * big the hash operational data will be. | |
335 | */ | |
4e8ae72a | 336 | tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0); |
af316fc4 DH |
337 | if (IS_ERR(tfm)) |
338 | return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm); | |
339 | ||
340 | desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); | |
341 | digest_size = crypto_shash_digestsize(tfm); | |
342 | ||
343 | if (digest_size != ctx->digest_len) { | |
344 | pr_debug("Digest size mismatch (%zx != %x)\n", | |
345 | digest_size, ctx->digest_len); | |
346 | ret = -EBADMSG; | |
347 | goto error_no_desc; | |
348 | } | |
349 | pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size); | |
350 | ||
351 | ret = -ENOMEM; | |
352 | desc = kzalloc(desc_size + digest_size, GFP_KERNEL); | |
353 | if (!desc) | |
354 | goto error_no_desc; | |
355 | ||
356 | desc->tfm = tfm; | |
357 | desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; | |
358 | ret = crypto_shash_init(desc); | |
359 | if (ret < 0) | |
360 | goto error; | |
361 | ||
362 | ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc); | |
363 | if (ret < 0) | |
364 | goto error; | |
365 | ||
366 | digest = (void *)desc + desc_size; | |
367 | ret = crypto_shash_final(desc, digest); | |
368 | if (ret < 0) | |
369 | goto error; | |
370 | ||
371 | pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest); | |
372 | ||
373 | /* Check that the PE file digest matches that in the MSCODE part of the | |
374 | * PKCS#7 certificate. | |
375 | */ | |
376 | if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) { | |
377 | pr_debug("Digest mismatch\n"); | |
378 | ret = -EKEYREJECTED; | |
379 | } else { | |
380 | pr_debug("The digests match!\n"); | |
381 | } | |
382 | ||
383 | error: | |
da7798a7 | 384 | kzfree(desc); |
af316fc4 DH |
385 | error_no_desc: |
386 | crypto_free_shash(tfm); | |
387 | kleave(" = %d", ret); | |
388 | return ret; | |
389 | } | |
390 | ||
26d1164b DH |
391 | /** |
392 | * verify_pefile_signature - Verify the signature on a PE binary image | |
393 | * @pebuf: Buffer containing the PE binary image | |
394 | * @pelen: Length of the binary image | |
e68503bd | 395 | * @trust_keys: Signing certificate(s) to use as starting points |
99db4435 | 396 | * @usage: The use to which the key is being put. |
26d1164b DH |
397 | * |
398 | * Validate that the certificate chain inside the PKCS#7 message inside the PE | |
399 | * binary image intersects keys we already know and trust. | |
400 | * | |
401 | * Returns, in order of descending priority: | |
402 | * | |
403 | * (*) -ELIBBAD if the image cannot be parsed, or: | |
404 | * | |
405 | * (*) -EKEYREJECTED if a signature failed to match for which we have a valid | |
406 | * key, or: | |
407 | * | |
408 | * (*) 0 if at least one signature chain intersects with the keys in the trust | |
409 | * keyring, or: | |
410 | * | |
411 | * (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a | |
412 | * chain. | |
413 | * | |
414 | * (*) -ENOKEY if we couldn't find a match for any of the signature chains in | |
415 | * the message. | |
416 | * | |
417 | * May also return -ENOMEM. | |
418 | */ | |
419 | int verify_pefile_signature(const void *pebuf, unsigned pelen, | |
e68503bd DH |
420 | struct key *trusted_keys, |
421 | enum key_being_used_for usage) | |
26d1164b DH |
422 | { |
423 | struct pefile_context ctx; | |
424 | int ret; | |
425 | ||
426 | kenter(""); | |
427 | ||
428 | memset(&ctx, 0, sizeof(ctx)); | |
429 | ret = pefile_parse_binary(pebuf, pelen, &ctx); | |
430 | if (ret < 0) | |
431 | return ret; | |
432 | ||
09dacbbd DH |
433 | ret = pefile_strip_sig_wrapper(pebuf, &ctx); |
434 | if (ret < 0) | |
435 | return ret; | |
436 | ||
e68503bd DH |
437 | ret = verify_pkcs7_signature(NULL, 0, |
438 | pebuf + ctx.sig_offset, ctx.sig_len, | |
bda850cd | 439 | trusted_keys, usage, |
e68503bd | 440 | mscode_parse, &ctx); |
4c0b4b1d DH |
441 | if (ret < 0) |
442 | goto error; | |
443 | ||
444 | pr_debug("Digest: %u [%*ph]\n", | |
445 | ctx.digest_len, ctx.digest_len, ctx.digest); | |
446 | ||
af316fc4 DH |
447 | /* Generate the digest and check against the PKCS7 certificate |
448 | * contents. | |
449 | */ | |
450 | ret = pefile_digest_pe(pebuf, pelen, &ctx); | |
3968280c DH |
451 | |
452 | error: | |
da7798a7 | 453 | kzfree(ctx.digest); |
3968280c | 454 | return ret; |
26d1164b | 455 | } |