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v6.2
  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 *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");
 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 = 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_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
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.
158	 */
159	ctx->sig_len = wrapper.length;
160	ctx->sig_offset += sizeof(wrapper);
161	ctx->sig_len -= sizeof(wrapper);
162	if (ctx->sig_len < 4) {
163		pr_debug("Signature data missing\n");
164		return -EKEYREJECTED;
165	}
166
167	/* What's left should be a PKCS#7 cert */
168	pkcs7 = pebuf + ctx->sig_offset;
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;
188	}
189
190check_len:
191	if (len <= ctx->sig_len) {
192		/* There may be padding */
193		ctx->sig_len = len;
194		return 0;
195	}
196not_pkcs7:
197	pr_debug("Signature data not PKCS#7\n");
198	return -ELIBBAD;
199}
200
201/*
202 * Compare two sections for canonicalisation.
203 */
204static 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 */
241static 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 */
318static 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
327	kenter(",%s", ctx->digest_algo);
328
329	/* Allocate the hashing algorithm we're going to need and find out how
330	 * big the hash operational data will be.
331	 */
332	tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0);
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;
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
378error:
379	kfree_sensitive(desc);
380error_no_desc:
381	crypto_free_shash(tfm);
382	kleave(" = %d", ret);
383	return ret;
384}
385
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
390 * @trust_keys: Signing certificate(s) to use as starting points
391 * @usage: The use to which the key is being put.
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 *
406 *  (*) -ENODATA if there is no signature present.
407 *
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 */
416int verify_pefile_signature(const void *pebuf, unsigned pelen,
417			    struct key *trusted_keys,
418			    enum key_being_used_for usage)
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
430	ret = pefile_strip_sig_wrapper(pebuf, &ctx);
431	if (ret < 0)
432		return ret;
433
434	ret = verify_pkcs7_signature(NULL, 0,
435				     pebuf + ctx.sig_offset, ctx.sig_len,
436				     trusted_keys, usage,
437				     mscode_parse, &ctx);
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
444	/* Generate the digest and check against the PKCS7 certificate
445	 * contents.
446	 */
447	ret = pefile_digest_pe(pebuf, pelen, &ctx);
448
449error:
450	kfree_sensitive(ctx.digest);
451	return ret;
452}
v5.9
  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 *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");
 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 = 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_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
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.
158	 */
159	ctx->sig_len = wrapper.length;
160	ctx->sig_offset += sizeof(wrapper);
161	ctx->sig_len -= sizeof(wrapper);
162	if (ctx->sig_len < 4) {
163		pr_debug("Signature data missing\n");
164		return -EKEYREJECTED;
165	}
166
167	/* What's left should be a PKCS#7 cert */
168	pkcs7 = pebuf + ctx->sig_offset;
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;
188	}
189
190check_len:
191	if (len <= ctx->sig_len) {
192		/* There may be padding */
193		ctx->sig_len = len;
194		return 0;
195	}
196not_pkcs7:
197	pr_debug("Signature data not PKCS#7\n");
198	return -ELIBBAD;
199}
200
201/*
202 * Compare two sections for canonicalisation.
203 */
204static 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 */
241static 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 */
318static 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
327	kenter(",%s", ctx->digest_algo);
328
329	/* Allocate the hashing algorithm we're going to need and find out how
330	 * big the hash operational data will be.
331	 */
332	tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0);
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;
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
378error:
379	kfree_sensitive(desc);
380error_no_desc:
381	crypto_free_shash(tfm);
382	kleave(" = %d", ret);
383	return ret;
384}
385
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
390 * @trust_keys: Signing certificate(s) to use as starting points
391 * @usage: The use to which the key is being put.
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 *
406 *  (*) -ENODATA if there is no signature present.
407 *
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 */
416int verify_pefile_signature(const void *pebuf, unsigned pelen,
417			    struct key *trusted_keys,
418			    enum key_being_used_for usage)
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
430	ret = pefile_strip_sig_wrapper(pebuf, &ctx);
431	if (ret < 0)
432		return ret;
433
434	ret = verify_pkcs7_signature(NULL, 0,
435				     pebuf + ctx.sig_offset, ctx.sig_len,
436				     trusted_keys, usage,
437				     mscode_parse, &ctx);
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
444	/* Generate the digest and check against the PKCS7 certificate
445	 * contents.
446	 */
447	ret = pefile_digest_pe(pebuf, pelen, &ctx);
448
449error:
450	kfree_sensitive(ctx.digest);
451	return ret;
452}