1 /*-
2  * Copyright (c) 2016 Kai Wang
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  */
26 
27 #include <assert.h>
28 #include <errno.h>
29 
30 #include "_libpe.h"
31 
32 ELFTC_VCSID("$Id: pe_rich.c 3312 2016-01-10 09:23:51Z kaiwang27 $");
33 
34 PE_RichHdr *
35 pe_rich_header(PE *pe)
36 {
37 
38 	if (pe == NULL) {
39 		errno = EINVAL;
40 		return (NULL);
41 	}
42 
43 	if (pe->pe_rh == NULL && pe->pe_stub_ex > 0 &&
44 	    (pe->pe_flags & LIBPE_F_LOAD_DOS_STUB) == 0) {
45 		assert((pe->pe_flags & LIBPE_F_SPECIAL_FILE) == 0);
46 		(void) libpe_read_msdos_stub(pe);
47 	}
48 
49 	if (pe->pe_rh == NULL) {
50 		errno = ENOENT;
51 		return (NULL);
52 	}
53 
54 	return (pe->pe_rh);
55 }
56 
57 static uint32_t
58 rol32(uint32_t n, int c)
59 {
60 
61 	c &= 0x1f;
62 
63 	return ((n << c) | (n >> (0x20 - c)));
64 }
65 
66 int
67 pe_rich_header_validate(PE *pe)
68 {
69 	PE_RichHdr *rh;
70 	uint32_t cksum;
71 	char *p;
72 	int i, off;
73 
74 	if (pe_rich_header(pe) == NULL)
75 		return (-1);
76 
77 	assert(pe->pe_rh_start != NULL);
78 
79 	/*
80 	 * Initial value of the checksum is the offset to the begin of
81 	 * the Rich header.
82 	 */
83 	cksum = pe->pe_rh_start - pe->pe_stub;
84 
85 	/*
86 	 * Add the bytes before the Rich header to the checksum, rotated
87 	 * left by the offset.
88 	 */
89 	for (p = pe->pe_stub; p < pe->pe_rh_start; p++) {
90 		/* Skip dh_lfanew. */
91 		off = p - pe->pe_stub;
92 		if (off >= 0x3c && off < 0x40)
93 			continue;
94 		cksum += rol32((unsigned char) *p, off);
95 	}
96 
97 	/* Add each compid rotated left by its count to the checksum. */
98 	rh = pe->pe_rh;
99 	for (i = 0; (uint32_t) i < rh->rh_total; i++)
100 		cksum += rol32(rh->rh_compid[i], rh->rh_cnt[i]);
101 
102 	/* Validate the checksum with the XOR mask stored after "Rich". */
103 	if (cksum == rh->rh_xor)
104 		return (1);
105 
106 	return (0);
107 }
108