summaryrefslogtreecommitdiffstats
path: root/crypto/asymmetric_keys/verify_pefile.c
blob: 2863984b67005080f5913410da7fc7ee1d287736 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
// SPDX-License-Identifier: GPL-2.0-or-later
/* Parse a signed PE binary
 *
 * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#define pr_fmt(fmt) "PEFILE: "fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/pe.h>
#include <linux/asn1.h>
#include <linux/verification.h>
#include <crypto/hash.h>
#include "verify_pefile.h"

/*
 * Parse a PE binary.
 */
static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
			       struct pefile_context *ctx)
{
	const struct mz_hdr *mz = pebuf;
	const struct pe_hdr *pe;
	const struct pe32_opt_hdr *pe32;
	const struct pe32plus_opt_hdr *pe64;
	const struct data_directory *ddir;
	const struct data_dirent *dde;
	const struct section_header *sec;
	size_t cursor, datalen = pelen;

	kenter("");

#define chkaddr(base, x, s)						\
	do {								\
		if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
			return -ELIBBAD;				\
	} while (0)

	chkaddr(0, 0, sizeof(*mz));
	if (mz->magic != MZ_MAGIC)
		return -ELIBBAD;
	cursor = sizeof(*mz);

	chkaddr(cursor, mz->peaddr, sizeof(*pe));
	pe = pebuf + mz->peaddr;
	if (pe->magic != PE_MAGIC)
		return -ELIBBAD;
	cursor = mz->peaddr + sizeof(*pe);

	chkaddr(0, cursor, sizeof(pe32->magic));
	pe32 = pebuf + cursor;
	pe64 = pebuf + cursor;

	switch (pe32->magic) {
	case PE_OPT_MAGIC_PE32:
		chkaddr(0, cursor, sizeof(*pe32));
		ctx->image_checksum_offset =
			(unsigned long)&pe32->csum - (unsigned long)pebuf;
		ctx->header_size = pe32->header_size;
		cursor += sizeof(*pe32);
		ctx->n_data_dirents = pe32->data_dirs;
		break;

	case PE_OPT_MAGIC_PE32PLUS:
		chkaddr(0, cursor, sizeof(*pe64));
		ctx->image_checksum_offset =
			(unsigned long)&pe64->csum - (unsigned long)pebuf;
		ctx->header_size = pe64->header_size;
		cursor += sizeof(*pe64);
		ctx->n_data_dirents = pe64->data_dirs;
		break;

	default:
		pr_warn("Unknown PEOPT magic = %04hx\n", pe32->magic);
		return -ELIBBAD;
	}

	pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
	pr_debug("header size = %x\n", ctx->header_size);

	if (cursor >= ctx->header_size || ctx->header_size >= datalen)
		return -ELIBBAD;

	if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
		return -ELIBBAD;

	ddir = pebuf + cursor;
	cursor += sizeof(*dde) * ctx->n_data_dirents;

	ctx->cert_dirent_offset =
		(unsigned long)&ddir->certs - (unsigned long)pebuf;
	ctx->certs_size = ddir->certs.size;

	if (!ddir->certs.virtual_address || !ddir->certs.size) {
		pr_warn("Unsigned PE binary\n");
		return -ENODATA;
	}

	chkaddr(ctx->header_size, ddir->certs.virtual_address,
		ddir->certs.size);
	ctx->sig_offset = ddir->certs.virtual_address;
	ctx->sig_len = ddir->certs.size;
	pr_debug("cert = %x @%x [%*ph]\n",
		 ctx->sig_len, ctx->sig_offset,
		 ctx->sig_len, pebuf + ctx->sig_offset);

	ctx->n_sections = pe->sections;
	if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
		return -ELIBBAD;
	ctx->secs = pebuf + cursor;

	return 0;
}

/*
 * Check and strip the PE wrapper from around the signature and check that the
 * remnant looks something like PKCS#7.
 */
static int pefile_strip_sig_wrapper(const void *pebuf,
				    struct pefile_context *ctx)
{
	struct win_certificate wrapper;
	const u8 *pkcs7;
	unsigned len;

	if (ctx->sig_len < sizeof(wrapper)) {
		pr_warn("Signature wrapper too short\n");
		return -ELIBBAD;
	}

	memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
	pr_debug("sig wrapper = { %x, %x, %x }\n",
		 wrapper.length, wrapper.revision, wrapper.cert_type);

	/* sbsign rounds up the length of certificate table (in optional
	 * header data directories) to 8 byte alignment.  However, the PE
	 * specification states that while entries are 8-byte aligned, this is
	 * not included in their length, and as a result, pesign has not
	 * rounded up since 0.110.
	 */
	if (wrapper.length > ctx->sig_len) {
		pr_warn("Signature wrapper bigger than sig len (%x > %x)\n",
			ctx->sig_len, wrapper.length);
		return -ELIBBAD;
	}
	if (wrapper.revision != WIN_CERT_REVISION_2_0) {
		pr_warn("Signature is not revision 2.0\n");
		return -ENOTSUPP;
	}
	if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
		pr_warn("Signature certificate type is not PKCS\n");
		return -ENOTSUPP;
	}

	/* It looks like the pkcs signature length in wrapper->length and the
	 * size obtained from the data dir entries, which lists the total size
	 * of certificate table, are both aligned to an octaword boundary, so
	 * we may have to deal with some padding.
	 */
	ctx->sig_len = wrapper.length;
	ctx->sig_offset += sizeof(wrapper);
	ctx->sig_len -= sizeof(wrapper);
	if (ctx->sig_len < 4) {
		pr_warn("Signature data missing\n");
		return -EKEYREJECTED;
	}

	/* What's left should be a PKCS#7 cert */
	pkcs7 = pebuf + ctx->sig_offset;
	if (pkcs7[0] != (ASN1_CONS_BIT | ASN1_SEQ))
		goto not_pkcs7;

	switch (pkcs7[1]) {
	case 0 ... 0x7f:
		len = pkcs7[1] + 2;
		goto check_len;
	case ASN1_INDEFINITE_LENGTH:
		return 0;
	case 0x81:
		len = pkcs7[2] + 3;
		goto check_len;
	case 0x82:
		len = ((pkcs7[2] << 8) | pkcs7[3]) + 4;
		goto check_len;
	case 0x83 ... 0xff:
		return -EMSGSIZE;
	default:
		goto not_pkcs7;
	}

check_len:
	if (len <= ctx->sig_len) {
		/* There may be padding */
		ctx->sig_len = len;
		return 0;
	}
not_pkcs7:
	pr_warn("Signature data not PKCS#7\n");
	return -ELIBBAD;
}

/*
 * Compare two sections for canonicalisation.
 */
static int pefile_compare_shdrs(const void *a, const void *b)
{
	const struct section_header *shdra = a;
	const struct section_header *shdrb = b;
	int rc;

	if (shdra->data_addr > shdrb->data_addr)
		return 1;
	if (shdrb->data_addr > shdra->data_addr)
		return -1;

	if (shdra->virtual_address > shdrb->virtual_address)
		return 1;
	if (shdrb->virtual_address > shdra->virtual_address)
		return -1;

	rc = strcmp(shdra->name, shdrb->name);
	if (rc != 0)
		return rc;

	if (shdra->virtual_size > shdrb->virtual_size)
		return 1;
	if (shdrb->virtual_size > shdra->virtual_size)
		return -1;

	if (shdra->raw_data_size > shdrb->raw_data_size)
		return 1;
	if (shdrb->raw_data_size > shdra->raw_data_size)
		return -1;

	return 0;
}

/*
 * Load the contents of the PE binary into the digest, leaving out the image
 * checksum and the certificate data block.
 */
static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen,
				     struct pefile_context *ctx,
				     struct shash_desc *desc)
{
	unsigned *canon, tmp, loop, i, hashed_bytes;
	int ret;

	/* Digest the header and data directory, but leave out the image
	 * checksum and the data dirent for the signature.
	 */
	ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset);
	if (ret < 0)
		return ret;

	tmp = ctx->image_checksum_offset + sizeof(uint32_t);
	ret = crypto_shash_update(desc, pebuf + tmp,
				  ctx->cert_dirent_offset - tmp);
	if (ret < 0)
		return ret;

	tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent);
	ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp);
	if (ret < 0)
		return ret;

	canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL);
	if (!canon)
		return -ENOMEM;

	/* We have to canonicalise the section table, so we perform an
	 * insertion sort.
	 */
	canon[0] = 0;
	for (loop = 1; loop < ctx->n_sections; loop++) {
		for (i = 0; i < loop; i++) {
			if (pefile_compare_shdrs(&ctx->secs[canon[i]],
						 &ctx->secs[loop]) > 0) {
				memmove(&canon[i + 1], &canon[i],
					(loop - i) * sizeof(canon[0]));
				break;
			}
		}
		canon[i] = loop;
	}

	hashed_bytes = ctx->header_size;
	for (loop = 0; loop < ctx->n_sections; loop++) {
		i = canon[loop];
		if (ctx->secs[i].raw_data_size == 0)
			continue;
		ret = crypto_shash_update(desc,
					  pebuf + ctx->secs[i].data_addr,
					  ctx->secs[i].raw_data_size);
		if (ret < 0) {
			kfree(canon);
			return ret;
		}
		hashed_bytes += ctx->secs[i].raw_data_size;
	}
	kfree(canon);

	if (pelen > hashed_bytes) {
		tmp = hashed_bytes + ctx->certs_size;
		ret = crypto_shash_update(desc,
					  pebuf + hashed_bytes,
					  pelen - tmp);
		if (ret < 0)
			return ret;
	}

	return 0;
}

/*
 * Digest the contents of the PE binary, leaving out the image checksum and the
 * certificate data block.
 */
static int pefile_digest_pe(const void *pebuf, unsigned int pelen,
			    struct pefile_context *ctx)
{
	struct crypto_shash *tfm;
	struct shash_desc *desc;
	size_t digest_size, desc_size;
	void *digest;
	int ret;

	kenter(",%s", ctx->digest_algo);

	/* Allocate the hashing algorithm we're going to need and find out how
	 * big the hash operational data will be.
	 */
	tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0);
	if (IS_ERR(tfm))
		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);

	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
	digest_size = crypto_shash_digestsize(tfm);

	if (digest_size != ctx->digest_len) {
		pr_warn("Digest size mismatch (%zx != %x)\n",
			digest_size, ctx->digest_len);
		ret = -EBADMSG;
		goto error_no_desc;
	}
	pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size);

	ret = -ENOMEM;
	desc = kzalloc(desc_size + digest_size, GFP_KERNEL);
	if (!desc)
		goto error_no_desc;

	desc->tfm   = tfm;
	ret = crypto_shash_init(desc);
	if (ret < 0)
		goto error;

	ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc);
	if (ret < 0)
		goto error;

	digest = (void *)desc + desc_size;
	ret = crypto_shash_final(desc, digest);
	if (ret < 0)
		goto error;

	pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest);

	/* Check that the PE file digest matches that in the MSCODE part of the
	 * PKCS#7 certificate.
	 */
	if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) {
		pr_warn("Digest mismatch\n");
		ret = -EKEYREJECTED;
	} else {
		pr_debug("The digests match!\n");
	}

error:
	kfree_sensitive(desc);
error_no_desc:
	crypto_free_shash(tfm);
	kleave(" = %d", ret);
	return ret;
}

/**
 * verify_pefile_signature - Verify the signature on a PE binary image
 * @pebuf: Buffer containing the PE binary image
 * @pelen: Length of the binary image
 * @trusted_keys: Signing certificate(s) to use as starting points
 * @usage: The use to which the key is being put.
 *
 * Validate that the certificate chain inside the PKCS#7 message inside the PE
 * binary image intersects keys we already know and trust.
 *
 * Returns, in order of descending priority:
 *
 *  (*) -ELIBBAD if the image cannot be parsed, or:
 *
 *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
 *	key, or:
 *
 *  (*) 0 if at least one signature chain intersects with the keys in the trust
 *	keyring, or:
 *
 *  (*) -ENODATA if there is no signature present.
 *
 *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
 *	chain.
 *
 *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
 *	the message.
 *
 * May also return -ENOMEM.
 */
int verify_pefile_signature(const void *pebuf, unsigned pelen,
			    struct key *trusted_keys,
			    enum key_being_used_for usage)
{
	struct pefile_context ctx;
	int ret;

	kenter("");

	memset(&ctx, 0, sizeof(ctx));
	ret = pefile_parse_binary(pebuf, pelen, &ctx);
	if (ret < 0)
		return ret;

	ret = pefile_strip_sig_wrapper(pebuf, &ctx);
	if (ret < 0)
		return ret;

	ret = verify_pkcs7_signature(NULL, 0,
				     pebuf + ctx.sig_offset, ctx.sig_len,
				     trusted_keys, usage,
				     mscode_parse, &ctx);
	if (ret < 0)
		goto error;

	pr_debug("Digest: %u [%*ph]\n",
		 ctx.digest_len, ctx.digest_len, ctx.digest);

	/* Generate the digest and check against the PKCS7 certificate
	 * contents.
	 */
	ret = pefile_digest_pe(pebuf, pelen, &ctx);

error:
	kfree_sensitive(ctx.digest);
	return ret;
}