1 /* Parse a signed PE binary
3 * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
12 #define pr_fmt(fmt) "PEFILE: "fmt
13 #include <linux/module.h>
14 #include <linux/kernel.h>
15 #include <linux/slab.h>
16 #include <linux/err.h>
18 #include <linux/asn1.h>
19 #include <linux/verification.h>
20 #include <crypto/hash.h>
21 #include "verify_pefile.h"
26 static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
27 struct pefile_context *ctx)
29 const struct mz_hdr *mz = pebuf;
30 const struct pe_hdr *pe;
31 const struct pe32_opt_hdr *pe32;
32 const struct pe32plus_opt_hdr *pe64;
33 const struct data_directory *ddir;
34 const struct data_dirent *dde;
35 const struct section_header *secs, *sec;
36 size_t cursor, datalen = pelen;
40 #define chkaddr(base, x, s) \
42 if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
46 chkaddr(0, 0, sizeof(*mz));
47 if (mz->magic != MZ_MAGIC)
51 chkaddr(cursor, mz->peaddr, sizeof(*pe));
52 pe = pebuf + mz->peaddr;
53 if (pe->magic != PE_MAGIC)
55 cursor = mz->peaddr + sizeof(*pe);
57 chkaddr(0, cursor, sizeof(pe32->magic));
58 pe32 = pebuf + cursor;
59 pe64 = pebuf + cursor;
61 switch (pe32->magic) {
62 case PE_OPT_MAGIC_PE32:
63 chkaddr(0, cursor, sizeof(*pe32));
64 ctx->image_checksum_offset =
65 (unsigned long)&pe32->csum - (unsigned long)pebuf;
66 ctx->header_size = pe32->header_size;
67 cursor += sizeof(*pe32);
68 ctx->n_data_dirents = pe32->data_dirs;
71 case PE_OPT_MAGIC_PE32PLUS:
72 chkaddr(0, cursor, sizeof(*pe64));
73 ctx->image_checksum_offset =
74 (unsigned long)&pe64->csum - (unsigned long)pebuf;
75 ctx->header_size = pe64->header_size;
76 cursor += sizeof(*pe64);
77 ctx->n_data_dirents = pe64->data_dirs;
81 pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic);
85 pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
86 pr_debug("header size = %x\n", ctx->header_size);
88 if (cursor >= ctx->header_size || ctx->header_size >= datalen)
91 if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
94 ddir = pebuf + cursor;
95 cursor += sizeof(*dde) * ctx->n_data_dirents;
97 ctx->cert_dirent_offset =
98 (unsigned long)&ddir->certs - (unsigned long)pebuf;
99 ctx->certs_size = ddir->certs.size;
101 if (!ddir->certs.virtual_address || !ddir->certs.size) {
102 pr_debug("Unsigned PE binary\n");
103 return -EKEYREJECTED;
106 chkaddr(ctx->header_size, ddir->certs.virtual_address,
108 ctx->sig_offset = ddir->certs.virtual_address;
109 ctx->sig_len = ddir->certs.size;
110 pr_debug("cert = %x @%x [%*ph]\n",
111 ctx->sig_len, ctx->sig_offset,
112 ctx->sig_len, pebuf + ctx->sig_offset);
114 ctx->n_sections = pe->sections;
115 if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
117 ctx->secs = secs = pebuf + cursor;
123 * Check and strip the PE wrapper from around the signature and check that the
124 * remnant looks something like PKCS#7.
126 static int pefile_strip_sig_wrapper(const void *pebuf,
127 struct pefile_context *ctx)
129 struct win_certificate wrapper;
133 if (ctx->sig_len < sizeof(wrapper)) {
134 pr_debug("Signature wrapper too short\n");
138 memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
139 pr_debug("sig wrapper = { %x, %x, %x }\n",
140 wrapper.length, wrapper.revision, wrapper.cert_type);
142 /* Both pesign and sbsign round up the length of certificate table
143 * (in optional header data directories) to 8 byte alignment.
145 if (round_up(wrapper.length, 8) != ctx->sig_len) {
146 pr_debug("Signature wrapper len wrong\n");
149 if (wrapper.revision != WIN_CERT_REVISION_2_0) {
150 pr_debug("Signature is not revision 2.0\n");
153 if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
154 pr_debug("Signature certificate type is not PKCS\n");
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.
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_debug("Signature data missing\n");
168 return -EKEYREJECTED;
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))
180 case ASN1_INDEFINITE_LENGTH:
186 len = ((pkcs7[2] << 8) | pkcs7[3]) + 4;
195 if (len <= ctx->sig_len) {
196 /* There may be padding */
201 pr_debug("Signature data not PKCS#7\n");
206 * Compare two sections for canonicalisation.
208 static int pefile_compare_shdrs(const void *a, const void *b)
210 const struct section_header *shdra = a;
211 const struct section_header *shdrb = b;
214 if (shdra->data_addr > shdrb->data_addr)
216 if (shdrb->data_addr > shdra->data_addr)
219 if (shdra->virtual_address > shdrb->virtual_address)
221 if (shdrb->virtual_address > shdra->virtual_address)
224 rc = strcmp(shdra->name, shdrb->name);
228 if (shdra->virtual_size > shdrb->virtual_size)
230 if (shdrb->virtual_size > shdra->virtual_size)
233 if (shdra->raw_data_size > shdrb->raw_data_size)
235 if (shdrb->raw_data_size > shdra->raw_data_size)
242 * Load the contents of the PE binary into the digest, leaving out the image
243 * checksum and the certificate data block.
245 static int pefile_digest_pe_contents(const void *pebuf, unsigned int pelen,
246 struct pefile_context *ctx,
247 struct shash_desc *desc)
249 unsigned *canon, tmp, loop, i, hashed_bytes;
252 /* Digest the header and data directory, but leave out the image
253 * checksum and the data dirent for the signature.
255 ret = crypto_shash_update(desc, pebuf, ctx->image_checksum_offset);
259 tmp = ctx->image_checksum_offset + sizeof(uint32_t);
260 ret = crypto_shash_update(desc, pebuf + tmp,
261 ctx->cert_dirent_offset - tmp);
265 tmp = ctx->cert_dirent_offset + sizeof(struct data_dirent);
266 ret = crypto_shash_update(desc, pebuf + tmp, ctx->header_size - tmp);
270 canon = kcalloc(ctx->n_sections, sizeof(unsigned), GFP_KERNEL);
274 /* We have to canonicalise the section table, so we perform an
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]));
290 hashed_bytes = ctx->header_size;
291 for (loop = 0; loop < ctx->n_sections; loop++) {
293 if (ctx->secs[i].raw_data_size == 0)
295 ret = crypto_shash_update(desc,
296 pebuf + ctx->secs[i].data_addr,
297 ctx->secs[i].raw_data_size);
302 hashed_bytes += ctx->secs[i].raw_data_size;
306 if (pelen > hashed_bytes) {
307 tmp = hashed_bytes + ctx->certs_size;
308 ret = crypto_shash_update(desc,
309 pebuf + hashed_bytes,
319 * Digest the contents of the PE binary, leaving out the image checksum and the
320 * certificate data block.
322 static int pefile_digest_pe(const void *pebuf, unsigned int pelen,
323 struct pefile_context *ctx)
325 struct crypto_shash *tfm;
326 struct shash_desc *desc;
327 size_t digest_size, desc_size;
331 kenter(",%s", ctx->digest_algo);
333 /* Allocate the hashing algorithm we're going to need and find out how
334 * big the hash operational data will be.
336 tfm = crypto_alloc_shash(ctx->digest_algo, 0, 0);
338 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
340 desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
341 digest_size = crypto_shash_digestsize(tfm);
343 if (digest_size != ctx->digest_len) {
344 pr_debug("Digest size mismatch (%zx != %x)\n",
345 digest_size, ctx->digest_len);
349 pr_debug("Digest: desc=%zu size=%zu\n", desc_size, digest_size);
352 desc = kzalloc(desc_size + digest_size, GFP_KERNEL);
357 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
358 ret = crypto_shash_init(desc);
362 ret = pefile_digest_pe_contents(pebuf, pelen, ctx, desc);
366 digest = (void *)desc + desc_size;
367 ret = crypto_shash_final(desc, digest);
371 pr_debug("Digest calc = [%*ph]\n", ctx->digest_len, digest);
373 /* Check that the PE file digest matches that in the MSCODE part of the
374 * PKCS#7 certificate.
376 if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) {
377 pr_debug("Digest mismatch\n");
380 pr_debug("The digests match!\n");
386 crypto_free_shash(tfm);
387 kleave(" = %d", ret);
392 * verify_pefile_signature - Verify the signature on a PE binary image
393 * @pebuf: Buffer containing the PE binary image
394 * @pelen: Length of the binary image
395 * @trust_keys: Signing certificate(s) to use as starting points
396 * @usage: The use to which the key is being put.
398 * Validate that the certificate chain inside the PKCS#7 message inside the PE
399 * binary image intersects keys we already know and trust.
401 * Returns, in order of descending priority:
403 * (*) -ELIBBAD if the image cannot be parsed, or:
405 * (*) -EKEYREJECTED if a signature failed to match for which we have a valid
408 * (*) 0 if at least one signature chain intersects with the keys in the trust
411 * (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
414 * (*) -ENOKEY if we couldn't find a match for any of the signature chains in
417 * May also return -ENOMEM.
419 int verify_pefile_signature(const void *pebuf, unsigned pelen,
420 struct key *trusted_keys,
421 enum key_being_used_for usage)
423 struct pefile_context ctx;
428 memset(&ctx, 0, sizeof(ctx));
429 ret = pefile_parse_binary(pebuf, pelen, &ctx);
433 ret = pefile_strip_sig_wrapper(pebuf, &ctx);
437 ret = verify_pkcs7_signature(NULL, 0,
438 pebuf + ctx.sig_offset, ctx.sig_len,
444 pr_debug("Digest: %u [%*ph]\n",
445 ctx.digest_len, ctx.digest_len, ctx.digest);
447 /* Generate the digest and check against the PKCS7 certificate
450 ret = pefile_digest_pe(pebuf, pelen, &ctx);