1 /*
2  * Copyright (C) 2017 The Android Open Source Project
3  *
4  * Permission is hereby granted, free of charge, to any person
5  * obtaining a copy of this software and associated documentation
6  * files (the "Software"), to deal in the Software without
7  * restriction, including without limitation the rights to use, copy,
8  * modify, merge, publish, distribute, sublicense, and/or sell copies
9  * of the Software, and to permit persons to whom the Software is
10  * furnished to do so, subject to the following conditions:
11  *
12  * The above copyright notice and this permission notice shall be
13  * included in all copies or substantial portions of the Software.
14  *
15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22  * SOFTWARE.
23  */
24 
25 #include "avb_user_verification.h"
26 
27 /* Maximum allow length (in bytes) of a partition name, including
28  * ab_suffix.
29  */
30 #define AVB_PART_NAME_MAX_SIZE 32
31 
32 /* Loads the toplevel AvbVBMetaImageHeader from the slot denoted by
33  * |ab_suffix| into |vbmeta_image|. No validation, verification, or
34  * byteswapping is performed.
35  *
36  * If successful, |true| is returned and the partition it was loaded
37  * from is returned in |out_partition_name| and the offset on said
38  * partition is returned in |out_vbmeta_offset|.
39  */
load_top_level_vbmeta_header(AvbOps * ops,const char * ab_suffix,uint8_t vbmeta_image[AVB_VBMETA_IMAGE_HEADER_SIZE],char out_partition_name[AVB_PART_NAME_MAX_SIZE],uint64_t * out_vbmeta_offset)40 static bool load_top_level_vbmeta_header(
41     AvbOps* ops,
42     const char* ab_suffix,
43     uint8_t vbmeta_image[AVB_VBMETA_IMAGE_HEADER_SIZE],
44     char out_partition_name[AVB_PART_NAME_MAX_SIZE],
45     uint64_t* out_vbmeta_offset) {
46   uint64_t vbmeta_offset = 0;
47   size_t num_read;
48   bool ret = false;
49   AvbIOResult io_res;
50 
51   /* Construct full partition name. */
52   if (!avb_str_concat(out_partition_name,
53                       AVB_PART_NAME_MAX_SIZE,
54                       "vbmeta",
55                       6,
56                       ab_suffix,
57                       avb_strlen(ab_suffix))) {
58     avb_error("Partition name and suffix does not fit.\n");
59     goto out;
60   }
61 
62   /* Only read the header, not the entire struct. */
63   io_res = ops->read_from_partition(ops,
64                                     out_partition_name,
65                                     vbmeta_offset,
66                                     AVB_VBMETA_IMAGE_HEADER_SIZE,
67                                     vbmeta_image,
68                                     &num_read);
69   if (io_res == AVB_IO_RESULT_ERROR_NO_SUCH_PARTITION) {
70     AvbFooter footer;
71 
72     /* Try looking for the vbmeta struct in 'boot' via the footer. */
73     if (!avb_str_concat(out_partition_name,
74                         AVB_PART_NAME_MAX_SIZE,
75                         "boot",
76                         4,
77                         ab_suffix,
78                         avb_strlen(ab_suffix))) {
79       avb_error("Partition name and suffix does not fit.\n");
80       goto out;
81     }
82     io_res = ops->read_from_partition(ops,
83                                       out_partition_name,
84                                       -AVB_FOOTER_SIZE,
85                                       AVB_FOOTER_SIZE,
86                                       &footer,
87                                       &num_read);
88     if (io_res != AVB_IO_RESULT_OK) {
89       avb_errorv("Error loading footer from partition '",
90                  out_partition_name,
91                  "'\n",
92                  NULL);
93       goto out;
94     }
95 
96     if (avb_memcmp(footer.magic, AVB_FOOTER_MAGIC, AVB_FOOTER_MAGIC_LEN) != 0) {
97       avb_errorv("Data from '",
98                  out_partition_name,
99                  "' does not look like a vbmeta footer.\n",
100                  NULL);
101       goto out;
102     }
103 
104     vbmeta_offset = avb_be64toh(footer.vbmeta_offset);
105     io_res = ops->read_from_partition(ops,
106                                       out_partition_name,
107                                       vbmeta_offset,
108                                       AVB_VBMETA_IMAGE_HEADER_SIZE,
109                                       vbmeta_image,
110                                       &num_read);
111   }
112 
113   if (io_res != AVB_IO_RESULT_OK) {
114     avb_errorv(
115         "Error loading from partition '", out_partition_name, "'\n", NULL);
116     goto out;
117   }
118 
119   if (out_vbmeta_offset != NULL) {
120     *out_vbmeta_offset = vbmeta_offset;
121   }
122 
123   ret = true;
124 
125 out:
126   return ret;
127 }
128 
avb_user_verification_get(AvbOps * ops,const char * ab_suffix,bool * out_verification_enabled)129 bool avb_user_verification_get(AvbOps* ops,
130                                const char* ab_suffix,
131                                bool* out_verification_enabled) {
132   uint8_t vbmeta_image[AVB_VBMETA_IMAGE_HEADER_SIZE]; /* 256 bytes. */
133   char partition_name[AVB_PART_NAME_MAX_SIZE];        /* 32 bytes. */
134   AvbVBMetaImageHeader* header;
135   uint32_t flags;
136   bool ret = false;
137 
138   if (!load_top_level_vbmeta_header(
139           ops, ab_suffix, vbmeta_image, partition_name, NULL)) {
140     goto out;
141   }
142 
143   if (avb_memcmp(vbmeta_image, AVB_MAGIC, AVB_MAGIC_LEN) != 0) {
144     avb_errorv("Data from '",
145                partition_name,
146                "' does not look like a vbmeta header.\n",
147                NULL);
148     goto out;
149   }
150 
151   /* Set/clear the VERIFICATION_DISABLED bit, as requested. */
152   header = (AvbVBMetaImageHeader*)vbmeta_image;
153   flags = avb_be32toh(header->flags);
154 
155   if (out_verification_enabled != NULL) {
156     *out_verification_enabled =
157         !(flags & AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED);
158   }
159 
160   ret = true;
161 
162 out:
163   return ret;
164 }
165 
avb_user_verification_set(AvbOps * ops,const char * ab_suffix,bool enable_verification)166 bool avb_user_verification_set(AvbOps* ops,
167                                const char* ab_suffix,
168                                bool enable_verification) {
169   uint8_t vbmeta_image[AVB_VBMETA_IMAGE_HEADER_SIZE]; /* 256 bytes. */
170   char partition_name[AVB_PART_NAME_MAX_SIZE];        /* 32 bytes. */
171   uint64_t vbmeta_offset;
172   AvbIOResult io_res;
173   AvbVBMetaImageHeader* header;
174   uint32_t flags;
175   bool ret = false;
176 
177   if (!load_top_level_vbmeta_header(
178           ops, ab_suffix, vbmeta_image, partition_name, &vbmeta_offset)) {
179     goto out;
180   }
181 
182   if (avb_memcmp(vbmeta_image, AVB_MAGIC, AVB_MAGIC_LEN) != 0) {
183     avb_errorv("Data from '",
184                partition_name,
185                "' does not look like a vbmeta header.\n",
186                NULL);
187     goto out;
188   }
189 
190   /* Set/clear the VERIFICATION_DISABLED bit, as requested. */
191   header = (AvbVBMetaImageHeader*)vbmeta_image;
192   flags = avb_be32toh(header->flags);
193   flags &= ~AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED;
194   if (!enable_verification) {
195     flags |= AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED;
196   }
197   header->flags = avb_htobe32(flags);
198 
199   /* Write the header. */
200   io_res = ops->write_to_partition(ops,
201                                    partition_name,
202                                    vbmeta_offset,
203                                    AVB_VBMETA_IMAGE_HEADER_SIZE,
204                                    vbmeta_image);
205   if (io_res != AVB_IO_RESULT_OK) {
206     avb_errorv("Error writing to partition '", partition_name, "'\n", NULL);
207     goto out;
208   }
209 
210   ret = true;
211 
212 out:
213   return ret;
214 }
215