Commit | Line | Data |
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b4d0d230 | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
26d1164b DH |
2 | /* Parse a signed PE binary |
3 | * | |
4 | * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved. | |
5 | * Written by David Howells (dhowells@redhat.com) | |
26d1164b DH |
6 | */ |
7 | ||
8 | #define pr_fmt(fmt) "PEFILE: "fmt | |
9 | #include <linux/module.h> | |
10 | #include <linux/kernel.h> | |
11 | #include <linux/slab.h> | |
12 | #include <linux/err.h> | |
13 | #include <linux/pe.h> | |
09dacbbd | 14 | #include <linux/asn1.h> |
e68503bd | 15 | #include <linux/verification.h> |
26d1164b DH |
16 | #include <crypto/hash.h> |
17 | #include "verify_pefile.h" | |
18 | ||
19 | /* | |
20 | * Parse a PE binary. | |
21 | */ | |
22 | static int pefile_parse_binary(const void *pebuf, unsigned int pelen, | |
23 | struct pefile_context *ctx) | |
24 | { | |
25 | const struct mz_hdr *mz = pebuf; | |
26 | const struct pe_hdr *pe; | |
27 | const struct pe32_opt_hdr *pe32; | |
28 | const struct pe32plus_opt_hdr *pe64; | |
29 | const struct data_directory *ddir; | |
30 | const struct data_dirent *dde; | |
31 | const struct section_header *secs, *sec; | |
32 | size_t cursor, datalen = pelen; | |
33 | ||
34 | kenter(""); | |
35 | ||
36 | #define chkaddr(base, x, s) \ | |
37 | do { \ | |
38 | if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \ | |
39 | return -ELIBBAD; \ | |
40 | } while (0) | |
41 | ||
42 | chkaddr(0, 0, sizeof(*mz)); | |
43 | if (mz->magic != MZ_MAGIC) | |
44 | return -ELIBBAD; | |
45 | cursor = sizeof(*mz); | |
46 | ||
47 | chkaddr(cursor, mz->peaddr, sizeof(*pe)); | |
48 | pe = pebuf + mz->peaddr; | |
49 | if (pe->magic != PE_MAGIC) | |
50 | return -ELIBBAD; | |
51 | cursor = mz->peaddr + sizeof(*pe); | |
52 | ||
53 | chkaddr(0, cursor, sizeof(pe32->magic)); | |
54 | pe32 = pebuf + cursor; | |
55 | pe64 = pebuf + cursor; | |
56 | ||
57 | switch (pe32->magic) { | |
58 | case PE_OPT_MAGIC_PE32: | |
59 | chkaddr(0, cursor, sizeof(*pe32)); | |
60 | ctx->image_checksum_offset = | |
61 | (unsigned long)&pe32->csum - (unsigned long)pebuf; | |
62 | ctx->header_size = pe32->header_size; | |
63 | cursor += sizeof(*pe32); | |
64 | ctx->n_data_dirents = pe32->data_dirs; | |
65 | break; | |
66 | ||
67 | case PE_OPT_MAGIC_PE32PLUS: | |
68 | chkaddr(0, cursor, sizeof(*pe64)); | |
69 | ctx->image_checksum_offset = | |
70 | (unsigned long)&pe64->csum - (unsigned long)pebuf; | |
71 | ctx->header_size = pe64->header_size; | |
72 | cursor += sizeof(*pe64); | |
73 | ctx->n_data_dirents = pe64->data_dirs; | |
74 | break; | |
75 | ||
76 | default: | |
77 | pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic); | |
78 | return -ELIBBAD; | |
79 | } | |
80 | ||
81 | pr_debug("checksum @ %x\n", ctx->image_checksum_offset); | |
82 | pr_debug("header size = %x\n", ctx->header_size); | |
83 | ||
84 | if (cursor >= ctx->header_size || ctx->header_size >= datalen) | |
85 | return -ELIBBAD; | |
86 | ||
87 | if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde)) | |
88 | return -ELIBBAD; | |
89 | ||
90 | ddir = pebuf + cursor; | |
91 | cursor += sizeof(*dde) * ctx->n_data_dirents; | |
92 | ||
93 | ctx->cert_dirent_offset = | |
94 | (unsigned long)&ddir->certs - (unsigned long)pebuf; | |
95 | ctx->certs_size = ddir->certs.size; | |
96 | ||
97 | if (!ddir->certs.virtual_address || !ddir->certs.size) { | |
98 | pr_debug("Unsigned PE binary\n"); | |
99d5cadf | 99 | return -ENODATA; |
26d1164b DH |
100 | } |
101 | ||
102 | chkaddr(ctx->header_size, ddir->certs.virtual_address, | |
103 | ddir->certs.size); | |
104 | ctx->sig_offset = ddir->certs.virtual_address; | |
105 | ctx->sig_len = ddir->certs.size; | |
106 | pr_debug("cert = %x @%x [%*ph]\n", | |
107 | ctx->sig_len, ctx->sig_offset, | |
108 | ctx->sig_len, pebuf + ctx->sig_offset); | |
109 | ||
110 | ctx->n_sections = pe->sections; | |
111 | if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec)) | |
112 | return -ELIBBAD; | |
113 | ctx->secs = secs = pebuf + cursor; | |
114 | ||
115 | return 0; | |
116 | } | |
117 | ||
09dacbbd DH |
118 | /* |
119 | * Check and strip the PE wrapper from around the signature and check that the | |
120 | * remnant looks something like PKCS#7. | |
121 | */ | |
122 | static int pefile_strip_sig_wrapper(const void *pebuf, | |
123 | struct pefile_context *ctx) | |
124 | { | |
125 | struct win_certificate wrapper; | |
126 | const u8 *pkcs7; | |
0aa04094 | 127 | unsigned len; |
09dacbbd DH |
128 | |
129 | if (ctx->sig_len < sizeof(wrapper)) { | |
130 | pr_debug("Signature wrapper too short\n"); | |
131 | return -ELIBBAD; | |
132 | } | |
133 | ||
134 | memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper)); | |
135 | pr_debug("sig wrapper = { %x, %x, %x }\n", | |
136 | wrapper.length, wrapper.revision, wrapper.cert_type); | |
137 | ||
138 | /* Both pesign and sbsign round up the length of certificate table | |
139 | * (in optional header data directories) to 8 byte alignment. | |
140 | */ | |
141 | if (round_up(wrapper.length, 8) != ctx->sig_len) { | |
142 | pr_debug("Signature wrapper len wrong\n"); | |
143 | return -ELIBBAD; | |
144 | } | |
145 | if (wrapper.revision != WIN_CERT_REVISION_2_0) { | |
146 | pr_debug("Signature is not revision 2.0\n"); | |
147 | return -ENOTSUPP; | |
148 | } | |
149 | if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) { | |
150 | pr_debug("Signature certificate type is not PKCS\n"); | |
151 | return -ENOTSUPP; | |
152 | } | |
153 | ||
0aa04094 DH |
154 | /* It looks like the pkcs signature length in wrapper->length and the |
155 | * size obtained from the data dir entries, which lists the total size | |
156 | * of certificate table, are both aligned to an octaword boundary, so | |
157 | * we may have to deal with some padding. | |
09dacbbd DH |
158 | */ |
159 | ctx->sig_len = wrapper.length; | |
160 | ctx->sig_offset += sizeof(wrapper); | |
161 | ctx->sig_len -= sizeof(wrapper); | |
0aa04094 | 162 | if (ctx->sig_len < 4) { |
09dacbbd DH |
163 | pr_debug("Signature data missing\n"); |
164 | return -EKEYREJECTED; | |
165 | } | |
166 | ||
0aa04094 | 167 | /* What's left should be a PKCS#7 cert */ |
09dacbbd | 168 | pkcs7 = pebuf + ctx->sig_offset; |
0aa04094 DH |
169 | if (pkcs7[0] != (ASN1_CONS_BIT | ASN1_SEQ)) |
170 | goto not_pkcs7; | |
171 | ||
172 | switch (pkcs7[1]) { | |
173 | case 0 ... 0x7f: | |
174 | len = pkcs7[1] + 2; | |
175 | goto check_len; | |
176 | case ASN1_INDEFINITE_LENGTH: | |
177 | return 0; | |
178 | case 0x81: | |
179 | len = pkcs7[2] + 3; | |
180 | goto check_len; | |
181 | case 0x82: | |
182 | len = ((pkcs7[2] << 8) | pkcs7[3]) + 4; | |
183 | goto check_len; | |
184 | case 0x83 ... 0xff: | |
185 | return -EMSGSIZE; | |
186 | default: | |
187 | goto not_pkcs7; | |
09dacbbd DH |
188 | } |
189 | ||
0aa04094 DH |
190 | check_len: |
191 | if (len <= ctx->sig_len) { | |
192 | /* There may be padding */ | |
193 | ctx->sig_len = len; | |
194 | return 0; | |
195 | } | |
196 | not_pkcs7: | |
09dacbbd DH |
197 | pr_debug("Signature data not PKCS#7\n"); |
198 | return -ELIBBAD; | |
199 | } | |
200 | ||
af316fc4 DH |
201 | /* |
202 | * Compare two sections for canonicalisation. | |
203 | */ | |
204 | static int pefile_compare_shdrs(const void *a, const void *b) | |
205 | { | |
206 | const struct section_header *shdra = a; | |
207 | const struct section_header *shdrb = b; | |
208 | int rc; | |
209 | ||
210 | if (shdra->data_addr > shdrb->data_addr) | |
211 | return 1; | |
212 | if (shdrb->data_addr > shdra->data_addr) | |
213 | return -1; | |
214 | ||
215 | if (shdra->virtual_address > shdrb->virtual_address) | |
216 | return 1; | |
217 | if (shdrb->virtual_address > shdra->virtual_address) | |
218 | return -1; | |
219 | ||
220 | rc = strcmp(shdra->name, shdrb->name); | |
221 | if (rc != 0) | |
222 | return rc; | |
223 | ||
224 | if (shdra->virtual_size > shdrb->virtual_size) | |
225 | return 1; | |
226 | if (shdrb->virtual_size > shdra->virtual_size) | |
227 | return -1; | |
228 | ||
229 | if (shdra->raw_data_size > shdrb->raw_data_size) | |
230 | return 1; | |
231 | if (shdrb->raw_data_size > shdra->raw_data_size) | |
232 | return -1; | |
233 | ||
234 | return 0; | |
235 | } | |
236 | ||
237 | /* | |
238 | * Load the contents of the PE binary into the digest, leaving out the image | |
239 | * checksum and the certificate data block. | |
240 | */ | |
241 | static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen, | |
242 | struct pefile_context *ctx, | |
243 | struct shash_desc *desc) | |
244 | { | |
245 | unsigned *canon, tmp, loop, i, hashed_bytes; | |
246 | int ret; | |
247 | ||
248 | /* Digest the header and data directory, but leave out the image | |
249 | * checksum and the data dirent for the signature. | |
250 | */ | |
251 | ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset); | |
252 | if (ret < 0) | |
253 | return ret; | |
254 | ||
255 | tmp = ctx->image_checksum_offset + sizeof(uint32_t); | |
256 | ret = crypto_shash_update(desc, pebuf + tmp, | |
257 | ctx->cert_dirent_offset - tmp); | |
258 | if (ret < 0) | |
259 | return ret; | |
260 | ||
261 | tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent); | |
262 | ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp); | |
263 | if (ret < 0) | |
264 | return ret; | |
265 | ||
266 | canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL); | |
267 | if (!canon) | |
268 | return -ENOMEM; | |
269 | ||
270 | /* We have to canonicalise the section table, so we perform an | |
271 | * insertion sort. | |
272 | */ | |
273 | canon[0] = 0; | |
274 | for (loop = 1; loop < ctx->n_sections; loop++) { | |
275 | for (i = 0; i < loop; i++) { | |
276 | if (pefile_compare_shdrs(&ctx->secs[canon[i]], | |
277 | &ctx->secs[loop]) > 0) { | |
278 | memmove(&canon[i + 1], &canon[i], | |
279 | (loop - i) * sizeof(canon[0])); | |
280 | break; | |
281 | } | |
282 | } | |
283 | canon[i] = loop; | |
284 | } | |
285 | ||
286 | hashed_bytes = ctx->header_size; | |
287 | for (loop = 0; loop < ctx->n_sections; loop++) { | |
288 | i = canon[loop]; | |
289 | if (ctx->secs[i].raw_data_size == 0) | |
290 | continue; | |
291 | ret = crypto_shash_update(desc, | |
292 | pebuf + ctx->secs[i].data_addr, | |
293 | ctx->secs[i].raw_data_size); | |
294 | if (ret < 0) { | |
295 | kfree(canon); | |
296 | return ret; | |
297 | } | |
298 | hashed_bytes += ctx->secs[i].raw_data_size; | |
299 | } | |
300 | kfree(canon); | |
301 | ||
302 | if (pelen > hashed_bytes) { | |
303 | tmp = hashed_bytes + ctx->certs_size; | |
304 | ret = crypto_shash_update(desc, | |
305 | pebuf + hashed_bytes, | |
306 | pelen - tmp); | |
307 | if (ret < 0) | |
308 | return ret; | |
309 | } | |
310 | ||
311 | return 0; | |
312 | } | |
313 | ||
314 | /* | |
315 | * Digest the contents of the PE binary, leaving out the image checksum and the | |
316 | * certificate data block. | |
317 | */ | |
318 | static int pefile_digest_pe(const void *pebuf, unsigned int pelen, | |
319 | struct pefile_context *ctx) | |
320 | { | |
321 | struct crypto_shash *tfm; | |
322 | struct shash_desc *desc; | |
323 | size_t digest_size, desc_size; | |
324 | void *digest; | |
325 | int ret; | |
326 | ||
4e8ae72a | 327 | kenter(",%s", ctx->digest_algo); |
af316fc4 DH |
328 | |
329 | /* Allocate the hashing algorithm we're going to need and find out how | |
330 | * big the hash operational data will be. | |
331 | */ | |
4e8ae72a | 332 | tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0); |
af316fc4 DH |
333 | if (IS_ERR(tfm)) |
334 | return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm); | |
335 | ||
336 | desc_size = crypto_shash_descsize(tfm) + sizeof(*desc); | |
337 | digest_size = crypto_shash_digestsize(tfm); | |
338 | ||
339 | if (digest_size != ctx->digest_len) { | |
340 | pr_debug("Digest size mismatch (%zx != %x)\n", | |
341 | digest_size, ctx->digest_len); | |
342 | ret = -EBADMSG; | |
343 | goto error_no_desc; | |
344 | } | |
345 | pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size); | |
346 | ||
347 | ret = -ENOMEM; | |
348 | desc = kzalloc(desc_size + digest_size, GFP_KERNEL); | |
349 | if (!desc) | |
350 | goto error_no_desc; | |
351 | ||
352 | desc->tfm = tfm; | |
af316fc4 DH |
353 | ret = crypto_shash_init(desc); |
354 | if (ret < 0) | |
355 | goto error; | |
356 | ||
357 | ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc); | |
358 | if (ret < 0) | |
359 | goto error; | |
360 | ||
361 | digest = (void *)desc + desc_size; | |
362 | ret = crypto_shash_final(desc, digest); | |
363 | if (ret < 0) | |
364 | goto error; | |
365 | ||
366 | pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest); | |
367 | ||
368 | /* Check that the PE file digest matches that in the MSCODE part of the | |
369 | * PKCS#7 certificate. | |
370 | */ | |
371 | if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) { | |
372 | pr_debug("Digest mismatch\n"); | |
373 | ret = -EKEYREJECTED; | |
374 | } else { | |
375 | pr_debug("The digests match!\n"); | |
376 | } | |
377 | ||
378 | error: | |
453431a5 | 379 | kfree_sensitive(desc); |
af316fc4 DH |
380 | error_no_desc: |
381 | crypto_free_shash(tfm); | |
382 | kleave(" = %d", ret); | |
383 | return ret; | |
384 | } | |
385 | ||
26d1164b DH |
386 | /** |
387 | * verify_pefile_signature - Verify the signature on a PE binary image | |
388 | * @pebuf: Buffer containing the PE binary image | |
389 | * @pelen: Length of the binary image | |
e68503bd | 390 | * @trust_keys: Signing certificate(s) to use as starting points |
99db4435 | 391 | * @usage: The use to which the key is being put. |
26d1164b DH |
392 | * |
393 | * Validate that the certificate chain inside the PKCS#7 message inside the PE | |
394 | * binary image intersects keys we already know and trust. | |
395 | * | |
396 | * Returns, in order of descending priority: | |
397 | * | |
398 | * (*) -ELIBBAD if the image cannot be parsed, or: | |
399 | * | |
400 | * (*) -EKEYREJECTED if a signature failed to match for which we have a valid | |
401 | * key, or: | |
402 | * | |
403 | * (*) 0 if at least one signature chain intersects with the keys in the trust | |
404 | * keyring, or: | |
405 | * | |
99d5cadf JB |
406 | * (*) -ENODATA if there is no signature present. |
407 | * | |
26d1164b DH |
408 | * (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a |
409 | * chain. | |
410 | * | |
411 | * (*) -ENOKEY if we couldn't find a match for any of the signature chains in | |
412 | * the message. | |
413 | * | |
414 | * May also return -ENOMEM. | |
415 | */ | |
416 | int verify_pefile_signature(const void *pebuf, unsigned pelen, | |
e68503bd DH |
417 | struct key *trusted_keys, |
418 | enum key_being_used_for usage) | |
26d1164b DH |
419 | { |
420 | struct pefile_context ctx; | |
421 | int ret; | |
422 | ||
423 | kenter(""); | |
424 | ||
425 | memset(&ctx, 0, sizeof(ctx)); | |
426 | ret = pefile_parse_binary(pebuf, pelen, &ctx); | |
427 | if (ret < 0) | |
428 | return ret; | |
429 | ||
09dacbbd DH |
430 | ret = pefile_strip_sig_wrapper(pebuf, &ctx); |
431 | if (ret < 0) | |
432 | return ret; | |
433 | ||
e68503bd DH |
434 | ret = verify_pkcs7_signature(NULL, 0, |
435 | pebuf + ctx.sig_offset, ctx.sig_len, | |
bda850cd | 436 | trusted_keys, usage, |
e68503bd | 437 | mscode_parse, &ctx); |
4c0b4b1d DH |
438 | if (ret < 0) |
439 | goto error; | |
440 | ||
441 | pr_debug("Digest: %u [%*ph]\n", | |
442 | ctx.digest_len, ctx.digest_len, ctx.digest); | |
443 | ||
af316fc4 DH |
444 | /* Generate the digest and check against the PKCS7 certificate |
445 | * contents. | |
446 | */ | |
447 | ret = pefile_digest_pe(pebuf, pelen, &ctx); | |
3968280c DH |
448 | |
449 | error: | |
453431a5 | 450 | kfree_sensitive(ctx.digest); |
3968280c | 451 | return ret; |
26d1164b | 452 | } |