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David Howells26d11642014-07-01 16:02:51 +01001/* 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>
David Howells09dacbb2014-07-01 16:02:51 +010018#include <linux/asn1.h>
David Howellse68503b2016-04-06 16:14:24 +010019#include <linux/verification.h>
David Howells26d11642014-07-01 16:02:51 +010020#include <crypto/hash.h>
21#include "verify_pefile.h"
22
23/*
24 * Parse a PE binary.
25 */
26static 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
David Howells09dacbb2014-07-01 16:02:51 +0100122/*
123 * Check and strip the PE wrapper from around the signature and check that the
124 * remnant looks something like PKCS#7.
125 */
126static int pefile_strip_sig_wrapper(const void *pebuf,
127 struct pefile_context *ctx)
128{
129 struct win_certificate wrapper;
130 const u8 *pkcs7;
David Howells0aa04092014-09-02 13:52:28 +0100131 unsigned len;
David Howells09dacbb2014-07-01 16:02:51 +0100132
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
David Howells0aa04092014-09-02 13:52:28 +0100158 /* 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.
David Howells09dacbb2014-07-01 16:02:51 +0100162 */
163 ctx->sig_len = wrapper.length;
164 ctx->sig_offset += sizeof(wrapper);
165 ctx->sig_len -= sizeof(wrapper);
David Howells0aa04092014-09-02 13:52:28 +0100166 if (ctx->sig_len < 4) {
David Howells09dacbb2014-07-01 16:02:51 +0100167 pr_debug("Signature data missing\n");
168 return -EKEYREJECTED;
169 }
170
David Howells0aa04092014-09-02 13:52:28 +0100171 /* What's left should be a PKCS#7 cert */
David Howells09dacbb2014-07-01 16:02:51 +0100172 pkcs7 = pebuf + ctx->sig_offset;
David Howells0aa04092014-09-02 13:52:28 +0100173 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;
David Howells09dacbb2014-07-01 16:02:51 +0100192 }
193
David Howells0aa04092014-09-02 13:52:28 +0100194check_len:
195 if (len <= ctx->sig_len) {
196 /* There may be padding */
197 ctx->sig_len = len;
198 return 0;
199 }
200not_pkcs7:
David Howells09dacbb2014-07-01 16:02:51 +0100201 pr_debug("Signature data not PKCS#7\n");
202 return -ELIBBAD;
203}
204
David Howellsaf316fc2014-07-01 16:02:52 +0100205/*
206 * Compare two sections for canonicalisation.
207 */
208static 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 */
245static 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 */
322static 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
David Howells4e8ae722016-03-03 21:49:27 +0000331 kenter(",%s", ctx->digest_algo);
David Howellsaf316fc2014-07-01 16:02:52 +0100332
333 /* Allocate the hashing algorithm we're going to need and find out how
334 * big the hash operational data will be.
335 */
David Howells4e8ae722016-03-03 21:49:27 +0000336 tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0);
David Howellsaf316fc2014-07-01 16:02:52 +0100337 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
383error:
384 kfree(desc);
385error_no_desc:
386 crypto_free_shash(tfm);
387 kleave(" = %d", ret);
388 return ret;
389}
390
David Howells26d11642014-07-01 16:02:51 +0100391/**
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
David Howellse68503b2016-04-06 16:14:24 +0100395 * @trust_keys: Signing certificate(s) to use as starting points
David Howells99db4432015-08-05 15:22:27 +0100396 * @usage: The use to which the key is being put.
David Howells26d11642014-07-01 16:02:51 +0100397 *
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 */
419int verify_pefile_signature(const void *pebuf, unsigned pelen,
David Howellse68503b2016-04-06 16:14:24 +0100420 struct key *trusted_keys,
421 enum key_being_used_for usage)
David Howells26d11642014-07-01 16:02:51 +0100422{
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
David Howells09dacbb2014-07-01 16:02:51 +0100433 ret = pefile_strip_sig_wrapper(pebuf, &ctx);
434 if (ret < 0)
435 return ret;
436
David Howellse68503b2016-04-06 16:14:24 +0100437 ret = verify_pkcs7_signature(NULL, 0,
438 pebuf + ctx.sig_offset, ctx.sig_len,
David Howellsbda850c2016-04-06 16:14:24 +0100439 trusted_keys, usage,
David Howellse68503b2016-04-06 16:14:24 +0100440 mscode_parse, &ctx);
David Howells4c0b4b12014-07-01 16:02:52 +0100441 if (ret < 0)
442 goto error;
443
444 pr_debug("Digest: %u [%*ph]\n",
445 ctx.digest_len, ctx.digest_len, ctx.digest);
446
David Howellsaf316fc2014-07-01 16:02:52 +0100447 /* Generate the digest and check against the PKCS7 certificate
448 * contents.
449 */
450 ret = pefile_digest_pe(pebuf, pelen, &ctx);
David Howells39682802014-07-01 16:02:51 +0100451
452error:
David Howellse68503b2016-04-06 16:14:24 +0100453 kfree(ctx.digest);
David Howells39682802014-07-01 16:02:51 +0100454 return ret;
David Howells26d11642014-07-01 16:02:51 +0100455}