1// SPDX-License-Identifier: GPL-2.0-or-later
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)
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>
14#include <linux/asn1.h>
15#include <linux/verification.h>
16#include <crypto/hash.h>
17#include "verify_pefile.h"
18
19/*
20 * Parse a PE binary.
21 */
22static 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 *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_warn("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_warn("Unsigned PE binary\n");
99		return -ENODATA;
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 = pebuf + cursor;
114
115	return 0;
116}
117
118/*
119 * Check and strip the PE wrapper from around the signature and check that the
120 * remnant looks something like PKCS#7.
121 */
122static int pefile_strip_sig_wrapper(const void *pebuf,
123				    struct pefile_context *ctx)
124{
125	struct win_certificate wrapper;
126	const u8 *pkcs7;
127	unsigned len;
128
129	if (ctx->sig_len < sizeof(wrapper)) {
130		pr_warn("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	/* sbsign rounds up the length of certificate table (in optional
139	 * header data directories) to 8 byte alignment.  However, the PE
140	 * specification states that while entries are 8-byte aligned, this is
141	 * not included in their length, and as a result, pesign has not
142	 * rounded up since 0.110.
143	 */
144	if (wrapper.length > ctx->sig_len) {
145		pr_warn("Signature wrapper bigger than sig len (%x > %x)\n",
146			ctx->sig_len, wrapper.length);
147		return -ELIBBAD;
148	}
149	if (wrapper.revision != WIN_CERT_REVISION_2_0) {
150		pr_warn("Signature is not revision 2.0\n");
151		return -ENOTSUPP;
152	}
153	if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
154		pr_warn("Signature certificate type is not PKCS\n");
155		return -ENOTSUPP;
156	}
157
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.
162	 */
163	ctx->sig_len = wrapper.length;
164	ctx->sig_offset += sizeof(wrapper);
165	ctx->sig_len -= sizeof(wrapper);
166	if (ctx->sig_len < 4) {
167		pr_warn("Signature data missing\n");
168		return -EKEYREJECTED;
169	}
170
171	/* What's left should be a PKCS#7 cert */
172	pkcs7 = pebuf + ctx->sig_offset;
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;
192	}
193
194check_len:
195	if (len <= ctx->sig_len) {
196		/* There may be padding */
197		ctx->sig_len = len;
198		return 0;
199	}
200not_pkcs7:
201	pr_warn("Signature data not PKCS#7\n");
202	return -ELIBBAD;
203}
204
205/*
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
331	kenter(",%s", ctx->digest_algo);
332
333	/* Allocate the hashing algorithm we're going to need and find out how
334	 * big the hash operational data will be.
335	 */
336	tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0);
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_warn("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	ret = crypto_shash_init(desc);
358	if (ret < 0)
359		goto error;
360
361	ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc);
362	if (ret < 0)
363		goto error;
364
365	digest = (void *)desc + desc_size;
366	ret = crypto_shash_final(desc, digest);
367	if (ret < 0)
368		goto error;
369
370	pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest);
371
372	/* Check that the PE file digest matches that in the MSCODE part of the
373	 * PKCS#7 certificate.
374	 */
375	if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) {
376		pr_warn("Digest mismatch\n");
377		ret = -EKEYREJECTED;
378	} else {
379		pr_debug("The digests match!\n");
380	}
381
382error:
383	kfree_sensitive(desc);
384error_no_desc:
385	crypto_free_shash(tfm);
386	kleave(" = %d", ret);
387	return ret;
388}
389
390/**
391 * verify_pefile_signature - Verify the signature on a PE binary image
392 * @pebuf: Buffer containing the PE binary image
393 * @pelen: Length of the binary image
394 * @trusted_keys: Signing certificate(s) to use as starting points
395 * @usage: The use to which the key is being put.
396 *
397 * Validate that the certificate chain inside the PKCS#7 message inside the PE
398 * binary image intersects keys we already know and trust.
399 *
400 * Returns, in order of descending priority:
401 *
402 *  (*) -ELIBBAD if the image cannot be parsed, or:
403 *
404 *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
405 *	key, or:
406 *
407 *  (*) 0 if at least one signature chain intersects with the keys in the trust
408 *	keyring, or:
409 *
410 *  (*) -ENODATA if there is no signature present.
411 *
412 *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
413 *	chain.
414 *
415 *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
416 *	the message.
417 *
418 * May also return -ENOMEM.
419 */
420int verify_pefile_signature(const void *pebuf, unsigned pelen,
421			    struct key *trusted_keys,
422			    enum key_being_used_for usage)
423{
424	struct pefile_context ctx;
425	int ret;
426
427	kenter("");
428
429	memset(&ctx, 0, sizeof(ctx));
430	ret = pefile_parse_binary(pebuf, pelen, &ctx);
431	if (ret < 0)
432		return ret;
433
434	ret = pefile_strip_sig_wrapper(pebuf, &ctx);
435	if (ret < 0)
436		return ret;
437
438	ret = verify_pkcs7_signature(NULL, 0,
439				     pebuf + ctx.sig_offset, ctx.sig_len,
440				     trusted_keys, usage,
441				     mscode_parse, &ctx);
442	if (ret < 0)
443		goto error;
444
445	pr_debug("Digest: %u [%*ph]\n",
446		 ctx.digest_len, ctx.digest_len, ctx.digest);
447
448	/* Generate the digest and check against the PKCS7 certificate
449	 * contents.
450	 */
451	ret = pefile_digest_pe(pebuf, pelen, &ctx);
452
453error:
454	kfree_sensitive(ctx.digest);
455	return ret;
456}
457