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 <crypto/pkcs7.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
;
132 if (ctx
->sig_len
< sizeof(wrapper
)) {
133 pr_debug("Signature wrapper too short\n");
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
);
141 /* Both pesign and sbsign round up the length of certificate table
142 * (in optional header data directories) to 8 byte alignment.
144 if (round_up(wrapper
.length
, 8) != ctx
->sig_len
) {
145 pr_debug("Signature wrapper len wrong\n");
148 if (wrapper
.revision
!= WIN_CERT_REVISION_2_0
) {
149 pr_debug("Signature is not revision 2.0\n");
152 if (wrapper
.cert_type
!= WIN_CERT_TYPE_PKCS_SIGNED_DATA
) {
153 pr_debug("Signature certificate type is not PKCS\n");
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.
161 * So set signature length field appropriately.
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
;
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))
178 if (pkcs7
[1] == 0x80)
184 pr_debug("Signature data not PKCS#7\n");
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
195 * Validate that the certificate chain inside the PKCS#7 message inside the PE
196 * binary image intersects keys we already know and trust.
198 * Returns, in order of descending priority:
200 * (*) -ELIBBAD if the image cannot be parsed, or:
202 * (*) -EKEYREJECTED if a signature failed to match for which we have a valid
205 * (*) 0 if at least one signature chain intersects with the keys in the trust
208 * (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
211 * (*) -ENOKEY if we couldn't find a match for any of the signature chains in
214 * May also return -ENOMEM.
216 int verify_pefile_signature(const void *pebuf
, unsigned pelen
,
217 struct key
*trusted_keyring
, bool *_trusted
)
219 struct pefile_context ctx
;
224 memset(&ctx
, 0, sizeof(ctx
));
225 ret
= pefile_parse_binary(pebuf
, pelen
, &ctx
);
229 ret
= pefile_strip_sig_wrapper(pebuf
, &ctx
);
233 return -ENOANO
; // Not yet complete