1 /* ----------------------------------------------------------------------- *
2 *
3 * Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
4 * Copyright 2010 Intel Corporation; author: H. Peter Anvin
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, Inc., 53 Temple Place Ste 330,
9 * Boston MA 02111-1307, USA; either version 2 of the License, or
10 * (at your option) any later version; incorporated herein by reference.
11 *
12 * ----------------------------------------------------------------------- */
13
14 /*
15 * setadv.c
16 *
17 * (Over)write a data item in the auxilliary data vector. To
18 * delete an item, set its length to zero.
19 *
20 * Return 0 on success, -1 on error, and set errno.
21 *
22 */
23 #define _GNU_SOURCE
24
25 #include <stdio.h>
26 #include <stdlib.h>
27 #include <stddef.h>
28 #include <stdint.h>
29 #include <string.h>
30 #include <errno.h>
31 #include "syslxint.h"
32 #include "syslxcom.h"
33 #include "syslxfs.h"
34
35 unsigned char syslinux_adv[2 * ADV_SIZE];
36
37 #define ADV_MAGIC1 0x5a2d2fa5 /* Head signature */
38 #define ADV_MAGIC2 0xa3041767 /* Total checksum */
39 #define ADV_MAGIC3 0xdd28bf64 /* Tail signature */
40
cleanup_adv(unsigned char * advbuf)41 static void cleanup_adv(unsigned char *advbuf)
42 {
43 int i;
44 uint32_t csum;
45
46 /* Make sure both copies agree, and update the checksum */
47 set_32((uint32_t *) advbuf, ADV_MAGIC1);
48
49 csum = ADV_MAGIC2;
50 for (i = 8; i < ADV_SIZE - 4; i += 4)
51 csum -= get_32((uint32_t *) (advbuf + i));
52
53 set_32((uint32_t *) (advbuf + 4), csum);
54 set_32((uint32_t *) (advbuf + ADV_SIZE - 4), ADV_MAGIC3);
55
56 memcpy(advbuf + ADV_SIZE, advbuf, ADV_SIZE);
57 }
58
syslinux_setadv(int tag,size_t size,const void * data)59 int syslinux_setadv(int tag, size_t size, const void *data)
60 {
61 uint8_t *p;
62 size_t left;
63 uint8_t advtmp[ADV_SIZE];
64
65 if ((unsigned)tag - 1 > 254) {
66 errno = EINVAL;
67 return -1; /* Impossible tag value */
68 }
69
70 if (size > 255) {
71 errno = ENOSPC; /* Max 255 bytes for a data item */
72 return -1;
73 }
74
75 left = ADV_LEN;
76 p = advtmp;
77 memcpy(p, syslinux_adv + 2 * 4, left); /* Make working copy */
78
79 while (left >= 2) {
80 uint8_t ptag = p[0];
81 size_t plen = p[1] + 2;
82
83 if (ptag == ADV_END)
84 break;
85
86 if (ptag == tag) {
87 /* Found our tag. Delete it. */
88
89 if (plen >= left) {
90 /* Entire remainder is our tag */
91 break;
92 }
93 memmove(p, p + plen, left - plen);
94 } else {
95 /* Not our tag */
96 if (plen > left)
97 break; /* Corrupt tag (overrun) - overwrite it */
98
99 left -= plen;
100 p += plen;
101 }
102 }
103
104 /* Now (p, left) reflects the position to write in and how much space
105 we have for our data. */
106
107 if (size) {
108 if (left < size + 2) {
109 errno = ENOSPC; /* Not enough space for data */
110 return -1;
111 }
112
113 *p++ = tag;
114 *p++ = size;
115 memcpy(p, data, size);
116 p += size;
117 left -= size + 2;
118 }
119
120 memset(p, 0, left);
121
122 /* If we got here, everything went OK, commit the write */
123 memcpy(syslinux_adv + 2 * 4, advtmp, ADV_LEN);
124 cleanup_adv(syslinux_adv);
125
126 return 0;
127 }
128
syslinux_reset_adv(unsigned char * advbuf)129 void syslinux_reset_adv(unsigned char *advbuf)
130 {
131 /* Create an all-zero ADV */
132 memset(advbuf + 2 * 4, 0, ADV_LEN);
133 cleanup_adv(advbuf);
134 }
135
adv_consistent(const unsigned char * p)136 static int adv_consistent(const unsigned char *p)
137 {
138 int i;
139 uint32_t csum;
140
141 if (get_32((uint32_t *) p) != ADV_MAGIC1 ||
142 get_32((uint32_t *) (p + ADV_SIZE - 4)) != ADV_MAGIC3)
143 return 0;
144
145 csum = 0;
146 for (i = 4; i < ADV_SIZE - 4; i += 4)
147 csum += get_32((uint32_t *) (p + i));
148
149 return csum == ADV_MAGIC2;
150 }
151
152 /*
153 * Verify that an in-memory ADV is consistent, making the copies consistent.
154 * If neither copy is OK, return -1 and call syslinux_reset_adv().
155 */
syslinux_validate_adv(unsigned char * advbuf)156 int syslinux_validate_adv(unsigned char *advbuf)
157 {
158 if (adv_consistent(advbuf + 0 * ADV_SIZE)) {
159 memcpy(advbuf + ADV_SIZE, advbuf, ADV_SIZE);
160 return 0;
161 } else if (adv_consistent(advbuf + 1 * ADV_SIZE)) {
162 memcpy(advbuf, advbuf + ADV_SIZE, ADV_SIZE);
163 return 0;
164 } else {
165 syslinux_reset_adv(advbuf);
166 return -1;
167 }
168 }
169