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David Howells26d11642014-07-01 16:02:51 +01001/* Parse a signed PE binary
2 *
3 * Copyright (C) 2014 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
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.
10 */
11
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>
17#include <linux/pe.h>
David Howells09dacbb2014-07-01 16:02:51 +010018#include <linux/asn1.h>
David Howells26d11642014-07-01 16:02:51 +010019#include <crypto/pkcs7.h>
20#include <crypto/hash.h>
21#include "verify_pefile.h"
22
23/*
24 * Parse a PE binary.
25 */
26static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
27 struct pefile_context *ctx)
28{
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;
37
38 kenter("");
39
40#define chkaddr(base, x, s) \
41 do { \
42 if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
43 return -ELIBBAD; \
44 } while (0)
45
46 chkaddr(0, 0, sizeof(*mz));
47 if (mz->magic != MZ_MAGIC)
48 return -ELIBBAD;
49 cursor = sizeof(*mz);
50
51 chkaddr(cursor, mz->peaddr, sizeof(*pe));
52 pe = pebuf + mz->peaddr;
53 if (pe->magic != PE_MAGIC)
54 return -ELIBBAD;
55 cursor = mz->peaddr + sizeof(*pe);
56
57 chkaddr(0, cursor, sizeof(pe32->magic));
58 pe32 = pebuf + cursor;
59 pe64 = pebuf + cursor;
60
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;
69 break;
70
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;
78 break;
79
80 default:
81 pr_debug("Unknown PEOPT magic = %04hx\n", pe32->magic);
82 return -ELIBBAD;
83 }
84
85 pr_debug("checksum @ %x\n", ctx->image_checksum_offset);
86 pr_debug("header size = %x\n", ctx->header_size);
87
88 if (cursor >= ctx->header_size || ctx->header_size >= datalen)
89 return -ELIBBAD;
90
91 if (ctx->n_data_dirents > (ctx->header_size - cursor) / sizeof(*dde))
92 return -ELIBBAD;
93
94 ddir = pebuf + cursor;
95 cursor += sizeof(*dde) * ctx->n_data_dirents;
96
97 ctx->cert_dirent_offset =
98 (unsigned long)&ddir->certs - (unsigned long)pebuf;
99 ctx->certs_size = ddir->certs.size;
100
101 if (!ddir->certs.virtual_address || !ddir->certs.size) {
102 pr_debug("Unsigned PE binary\n");
103 return -EKEYREJECTED;
104 }
105
106 chkaddr(ctx->header_size, ddir->certs.virtual_address,
107 ddir->certs.size);
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);
113
114 ctx->n_sections = pe->sections;
115 if (ctx->n_sections > (ctx->header_size - cursor) / sizeof(*sec))
116 return -ELIBBAD;
117 ctx->secs = secs = pebuf + cursor;
118
119 return 0;
120}
121
David Howells09dacbb2014-07-01 16:02:51 +0100122/*
123 * Check and strip the PE wrapper from around the signature and check that the
124 * remnant looks something like PKCS#7.
125 */
126static int pefile_strip_sig_wrapper(const void *pebuf,
127 struct pefile_context *ctx)
128{
129 struct win_certificate wrapper;
130 const u8 *pkcs7;
131
132 if (ctx->sig_len < sizeof(wrapper)) {
133 pr_debug("Signature wrapper too short\n");
134 return -ELIBBAD;
135 }
136
137 memcpy(&wrapper, pebuf + ctx->sig_offset, sizeof(wrapper));
138 pr_debug("sig wrapper = { %x, %x, %x }\n",
139 wrapper.length, wrapper.revision, wrapper.cert_type);
140
141 /* Both pesign and sbsign round up the length of certificate table
142 * (in optional header data directories) to 8 byte alignment.
143 */
144 if (round_up(wrapper.length, 8) != ctx->sig_len) {
145 pr_debug("Signature wrapper len wrong\n");
146 return -ELIBBAD;
147 }
148 if (wrapper.revision != WIN_CERT_REVISION_2_0) {
149 pr_debug("Signature is not revision 2.0\n");
150 return -ENOTSUPP;
151 }
152 if (wrapper.cert_type != WIN_CERT_TYPE_PKCS_SIGNED_DATA) {
153 pr_debug("Signature certificate type is not PKCS\n");
154 return -ENOTSUPP;
155 }
156
157 /* Looks like actual pkcs signature length is in wrapper->length.
158 * size obtained from data dir entries lists the total size of
159 * certificate table which is also aligned to octawrod boundary.
160 *
161 * So set signature length field appropriately.
162 */
163 ctx->sig_len = wrapper.length;
164 ctx->sig_offset += sizeof(wrapper);
165 ctx->sig_len -= sizeof(wrapper);
166 if (ctx->sig_len == 0) {
167 pr_debug("Signature data missing\n");
168 return -EKEYREJECTED;
169 }
170
171 /* What's left should a PKCS#7 cert */
172 pkcs7 = pebuf + ctx->sig_offset;
173 if (pkcs7[0] == (ASN1_CONS_BIT | ASN1_SEQ)) {
174 if (pkcs7[1] == 0x82 &&
175 pkcs7[2] == (((ctx->sig_len - 4) >> 8) & 0xff) &&
176 pkcs7[3] == ((ctx->sig_len - 4) & 0xff))
177 return 0;
178 if (pkcs7[1] == 0x80)
179 return 0;
180 if (pkcs7[1] > 0x82)
181 return -EMSGSIZE;
182 }
183
184 pr_debug("Signature data not PKCS#7\n");
185 return -ELIBBAD;
186}
187
David Howells26d11642014-07-01 16:02:51 +0100188/**
189 * verify_pefile_signature - Verify the signature on a PE binary image
190 * @pebuf: Buffer containing the PE binary image
191 * @pelen: Length of the binary image
192 * @trust_keyring: Signing certificates to use as starting points
193 * @_trusted: Set to true if trustworth, false otherwise
194 *
195 * Validate that the certificate chain inside the PKCS#7 message inside the PE
196 * binary image intersects keys we already know and trust.
197 *
198 * Returns, in order of descending priority:
199 *
200 * (*) -ELIBBAD if the image cannot be parsed, or:
201 *
202 * (*) -EKEYREJECTED if a signature failed to match for which we have a valid
203 * key, or:
204 *
205 * (*) 0 if at least one signature chain intersects with the keys in the trust
206 * keyring, or:
207 *
208 * (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
209 * chain.
210 *
211 * (*) -ENOKEY if we couldn't find a match for any of the signature chains in
212 * the message.
213 *
214 * May also return -ENOMEM.
215 */
216int verify_pefile_signature(const void *pebuf, unsigned pelen,
217 struct key *trusted_keyring, bool *_trusted)
218{
219 struct pefile_context ctx;
220 int ret;
221
222 kenter("");
223
224 memset(&ctx, 0, sizeof(ctx));
225 ret = pefile_parse_binary(pebuf, pelen, &ctx);
226 if (ret < 0)
227 return ret;
228
David Howells09dacbb2014-07-01 16:02:51 +0100229 ret = pefile_strip_sig_wrapper(pebuf, &ctx);
230 if (ret < 0)
231 return ret;
232
David Howells26d11642014-07-01 16:02:51 +0100233 return -ENOANO; // Not yet complete
234}