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 */
pefile_parse_binary(const void * pebuf,unsigned int pelen,struct pefile_context * ctx)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");
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 */
pefile_strip_sig_wrapper(const void * pebuf,struct pefile_context * ctx)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;
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
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:
197 pr_debug("Signature data not PKCS#7\n");
198 return -ELIBBAD;
199 }
200
201 /*
202 * Compare two sections for canonicalisation.
203 */
pefile_compare_shdrs(const void * a,const void * b)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 */
pefile_digest_pe_contents(const void * pebuf,unsigned int pelen,struct pefile_context * ctx,struct shash_desc * desc)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 */
pefile_digest_pe(const void * pebuf,unsigned int pelen,struct pefile_context * ctx)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
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
378 error:
379 kfree_sensitive(desc);
380 error_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 */
verify_pefile_signature(const void * pebuf,unsigned pelen,struct key * trusted_keys,enum key_being_used_for usage)416 int 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
449 error:
450 kfree_sensitive(ctx.digest);
451 return ret;
452 }
453