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_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 = 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_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
194 check_len:
195 if (len <= ctx->sig_len) {
196 /* There may be padding */
197 ctx->sig_len = len;
198 return 0;
199 }
200 not_pkcs7:
201 pr_warn("Signature data not PKCS#7\n");
202 return -ELIBBAD;
203 }
204
205 /*
206 * Compare two sections for canonicalisation.
207 */
pefile_compare_shdrs(const void * a,const void * b)208 static 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 */
pefile_digest_pe_contents(const void * pebuf,unsigned int pelen,struct pefile_context * ctx,struct shash_desc * desc)245 static 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 */
pefile_digest_pe(const void * pebuf,unsigned int pelen,struct pefile_context * ctx)322 static 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
382 error:
383 kfree_sensitive(desc);
384 error_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 */
verify_pefile_signature(const void * pebuf,unsigned pelen,struct key * trusted_keys,enum key_being_used_for usage)420 int 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
453 error:
454 kfree_sensitive(ctx.digest);
455 return ret;
456 }
457