summaryrefslogtreecommitdiff
path: root/crypto/asymmetric_keys/verify_pefile.c
blob: 13f3b44b5046f2d9257087b48d80b4dd162d0a51 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
/* Parse a signed PE binary
 *
 * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#define pr_fmt(fmt) "PEFILE: "fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/pe.h>
#include <linux/asn1.h>
#include <crypto/pkcs7.h>
#include <crypto/hash.h>
#include "verify_pefile.h"

/*
 * Parse a PE binary.
 */
static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
			       struct pefile_context *ctx)
{
	const struct mz_hdr *mz = pebuf;
	const struct pe_hdr *pe;
	const struct pe32_opt_hdr *pe32;
	const struct pe32plus_opt_hdr *pe64;
	const struct data_directory *ddir;
	const struct data_dirent *dde;
	const struct section_header *secs, *sec;
	size_t cursor, datalen = pelen;

	kenter("");

#define chkaddr(base, x, s)						\
	do {								\
		if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
			return -ELIBBAD;				\
	} while (0)

	chkaddr(0, 0, sizeof(*mz));
	if (mz->magic != MZ_MAGIC)
		return -ELIBBAD;
	cursor = sizeof(*mz);

	chkaddr(cursor, mz->peaddr, sizeof(*pe));
	pe = pebuf + mz->peaddr;
	if (pe->magic != PE_MAGIC)
		return -ELIBBAD;
	cursor = mz->peaddr + sizeof(*pe);

	chkaddr(0, cursor, sizeof(pe32->magic));
	pe32 = pebuf + cursor;
	pe64 = pebuf + cursor;

	switch (pe32->magic) {
	case PE_OPT_MAGIC_PE32:
		chkaddr(0, cursor, sizeof(*pe32));
		ctx->image_checksum_offset =
			(unsigned long)&pe32->csum - (unsigned long)pebuf;
		ctx->header_size = pe32->header_size;
		cursor += sizeof(*pe32);
		ctx->n_data_dirents = pe32->data_dirs;
		break;

	case PE_OPT_MAGIC_PE32PLUS:
		chkaddr(0, cursor, sizeof(*pe64));
		ctx->image_checksum_offset =
			(unsigned long)&pe64->csum - (unsigned long)pebuf;
		ctx->header_size = pe64->header_size;
		cursor += sizeof(*pe64);
		ctx->n_data_dirents = pe64->data_dirs;
		break;

	default:
		pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic);
		return -ELIBBAD;
	}

	pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
	pr_debug("header size = %x\n", ctx->header_size);

	if (cursor >= ctx->header_size || ctx->header_size >= datalen)
		return -ELIBBAD;

	if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
		return -ELIBBAD;

	ddir = pebuf + cursor;
	cursor += sizeof(*dde) * ctx->n_data_dirents;

	ctx->cert_dirent_offset =
		(unsigned long)&ddir->certs - (unsigned long)pebuf;
	ctx->certs_size = ddir->certs.size;

	if (!ddir->certs.virtual_address || !ddir->certs.size) {
		pr_debug("Unsigned PE binary\n");
		return -EKEYREJECTED;
	}

	chkaddr(ctx->header_size, ddir->certs.virtual_address,
		ddir->certs.size);
	ctx->sig_offset = ddir->certs.virtual_address;
	ctx->sig_len = ddir->certs.size;
	pr_debug("cert = %x @%x [%*ph]\n",
		 ctx->sig_len, ctx->sig_offset,
		 ctx->sig_len, pebuf + ctx->sig_offset);

	ctx->n_sections = pe->sections;
	if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
		return -ELIBBAD;
	ctx->secs = secs = pebuf + cursor;

	return 0;
}

/*
 * Check and strip the PE wrapper from around the signature and check that the
 * remnant looks something like PKCS#7.
 */
static int pefile_strip_sig_wrapper(const void *pebuf,
				    struct pefile_context *ctx)
{
	struct win_certificate wrapper;
	const u8 *pkcs7;

	if (ctx->sig_len < sizeof(wrapper)) {
		pr_debug("Signature wrapper too short\n");
		return -ELIBBAD;
	}

	memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
	pr_debug("sig wrapper = { %x, %x, %x }\n",
		 wrapper.length, wrapper.revision, wrapper.cert_type);

	/* Both pesign and sbsign round up the length of certificate table
	 * (in optional header data directories) to 8 byte alignment.
	 */
	if (round_up(wrapper.length, 8) != ctx->sig_len) {
		pr_debug("Signature wrapper len wrong\n");
		return -ELIBBAD;
	}
	if (wrapper.revision != WIN_CERT_REVISION_2_0) {
		pr_debug("Signature is not revision 2.0\n");
		return -ENOTSUPP;
	}
	if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
		pr_debug("Signature certificate type is not PKCS\n");
		return -ENOTSUPP;
	}

	/* Looks like actual pkcs signature length is in wrapper->length.
	 * size obtained from data dir entries lists the total size of
	 * certificate table which is also aligned to octawrod boundary.
	 *
	 * So set signature length field appropriately.
	 */
	ctx->sig_len = wrapper.length;
	ctx->sig_offset += sizeof(wrapper);
	ctx->sig_len -= sizeof(wrapper);
	if (ctx->sig_len == 0) {
		pr_debug("Signature data missing\n");
		return -EKEYREJECTED;
	}

	/* What's left should a PKCS#7 cert */
	pkcs7 = pebuf + ctx->sig_offset;
	if (pkcs7[0] == (ASN1_CONS_BIT | ASN1_SEQ)) {
		if (pkcs7[1] == 0x82 &&
		    pkcs7[2] == (((ctx->sig_len - 4) >> 8) & 0xff) &&
		    pkcs7[3] ==  ((ctx->sig_len - 4)       & 0xff))
			return 0;
		if (pkcs7[1] == 0x80)
			return 0;
		if (pkcs7[1] > 0x82)
			return -EMSGSIZE;
	}

	pr_debug("Signature data not PKCS#7\n");
	return -ELIBBAD;
}

/**
 * verify_pefile_signature - Verify the signature on a PE binary image
 * @pebuf: Buffer containing the PE binary image
 * @pelen: Length of the binary image
 * @trust_keyring: Signing certificates to use as starting points
 * @_trusted: Set to true if trustworth, false otherwise
 *
 * Validate that the certificate chain inside the PKCS#7 message inside the PE
 * binary image intersects keys we already know and trust.
 *
 * Returns, in order of descending priority:
 *
 *  (*) -ELIBBAD if the image cannot be parsed, or:
 *
 *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
 *	key, or:
 *
 *  (*) 0 if at least one signature chain intersects with the keys in the trust
 *	keyring, or:
 *
 *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
 *	chain.
 *
 *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
 *	the message.
 *
 * May also return -ENOMEM.
 */
int verify_pefile_signature(const void *pebuf, unsigned pelen,
			    struct key *trusted_keyring, bool *_trusted)
{
	struct pkcs7_message *pkcs7;
	struct pefile_context ctx;
	const void *data;
	size_t datalen;
	int ret;

	kenter("");

	memset(&ctx, 0, sizeof(ctx));
	ret = pefile_parse_binary(pebuf, pelen, &ctx);
	if (ret < 0)
		return ret;

	ret = pefile_strip_sig_wrapper(pebuf, &ctx);
	if (ret < 0)
		return ret;

	pkcs7 = pkcs7_parse_message(pebuf + ctx.sig_offset, ctx.sig_len);
	if (IS_ERR(pkcs7))
		return PTR_ERR(pkcs7);
	ctx.pkcs7 = pkcs7;

	ret = pkcs7_get_content_data(ctx.pkcs7, &data, &datalen, false);
	if (ret < 0 || datalen == 0) {
		pr_devel("PKCS#7 message does not contain data\n");
		ret = -EBADMSG;
		goto error;
	}

	ret = -ENOANO; // Not yet complete

error:
	pkcs7_free_message(ctx.pkcs7);
	return ret;
}