1 /*
2  * Copyright (C) 2020 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #include "avb_utils.h"
18 
19 #include <android-base/strings.h>
20 #include <libavb/libavb.h>
21 
22 #include "fec_private.h"
23 
24 int parse_vbmeta_from_footer(fec_handle *f, std::vector<uint8_t> *vbmeta) {
25     if (f->size <= AVB_FOOTER_SIZE) {
26         debug("file size not large enough to be avb images:" PRIu64, f->size);
27         return -1;
28     }
29 
30     AvbFooter footer_read;
31     if (!raw_pread(f->fd, &footer_read, AVB_FOOTER_SIZE,
32                    f->size - AVB_FOOTER_SIZE)) {
33         error("failed to read footer: %s", strerror(errno));
34         return -1;
35     }
36 
37     AvbFooter footer;
38     if (!avb_footer_validate_and_byteswap(&footer_read, &footer)) {
39         debug("invalid avb footer");
40         return -1;
41     }
42     uint64_t vbmeta_offset = footer.vbmeta_offset;
43     uint64_t vbmeta_size = footer.vbmeta_size;
44     check(vbmeta_offset <= f->size - sizeof(footer) - vbmeta_size);
45 
46     std::vector<uint8_t> vbmeta_data(vbmeta_size, 0);
47     // TODO(xunchang) handle the sparse image with libsparse.
48     if (!raw_pread(f->fd, vbmeta_data.data(), vbmeta_data.size(),
49                    vbmeta_offset)) {
50         error("failed to read avb vbmeta: %s", strerror(errno));
51         return -1;
52     }
53 
54     if (auto status = avb_vbmeta_image_verify(
55             vbmeta_data.data(), vbmeta_data.size(), nullptr, nullptr);
56         status != AVB_VBMETA_VERIFY_RESULT_OK &&
57         status != AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED) {
58         error("failed to verify avb vbmeta, status: %d", status);
59         return -1;
60     }
61     *vbmeta = std::move(vbmeta_data);
62     return 0;
63 }
64 
65 int parse_avb_image(fec_handle *f, const std::vector<uint8_t> &vbmeta) {
66     // TODO(xunchang) check if avb verification or hashtree is disabled.
67 
68     // Look for the hashtree descriptor, we expect exactly one descriptor in
69     // vbmeta.
70     // TODO(xunchang) handle the image with AvbHashDescriptor.
71     auto parse_descriptor = [](const AvbDescriptor *descriptor,
72                                void *user_data) {
73         if (descriptor &&
74             avb_be64toh(descriptor->tag) == AVB_DESCRIPTOR_TAG_HASHTREE) {
75             auto desp = static_cast<const AvbDescriptor **>(user_data);
76             *desp = descriptor;
77             return false;
78         }
79         return true;
80     };
81 
82     const AvbHashtreeDescriptor *hashtree_descriptor_ptr = nullptr;
83     avb_descriptor_foreach(vbmeta.data(), vbmeta.size(), parse_descriptor,
84                            &hashtree_descriptor_ptr);
85     if (!hashtree_descriptor_ptr) {
86         error("failed to find avb hashtree descriptor");
87         return -1;
88     }
89 
90     AvbHashtreeDescriptor hashtree_descriptor;
91     if (!avb_hashtree_descriptor_validate_and_byteswap(hashtree_descriptor_ptr,
92                                                        &hashtree_descriptor)) {
93         error("failed to verify avb hashtree descriptor");
94         return -1;
95     }
96 
97     // The partition name, salt, root append right after the hashtree
98     // descriptor.
99     auto read_ptr = reinterpret_cast<const uint8_t *>(hashtree_descriptor_ptr);
100     // Calculate the offset with respect to the vbmeta; and check both the
101     // salt & root are within the range.
102     uint32_t salt_offset =
103         sizeof(AvbHashtreeDescriptor) + hashtree_descriptor.partition_name_len;
104     uint32_t root_offset = salt_offset + hashtree_descriptor.salt_len;
105     check(hashtree_descriptor.salt_len < vbmeta.size());
106     check(salt_offset < vbmeta.size() - hashtree_descriptor.salt_len);
107     check(hashtree_descriptor.root_digest_len < vbmeta.size());
108     check(root_offset < vbmeta.size() - hashtree_descriptor.root_digest_len);
109     std::vector<uint8_t> salt(
110         read_ptr + salt_offset,
111         read_ptr + salt_offset + hashtree_descriptor.salt_len);
112     std::vector<uint8_t> root_hash(
113         read_ptr + root_offset,
114         read_ptr + root_offset + hashtree_descriptor.root_digest_len);
115 
116     // Expect the AVB image has the format:
117     // 1. hashtree
118     // 2. ecc data
119     // 3. vbmeta
120     // 4. avb footer
121     check(hashtree_descriptor.fec_offset ==
122           hashtree_descriptor.tree_offset + hashtree_descriptor.tree_size);
123     check(hashtree_descriptor.fec_offset <=
124           f->size - hashtree_descriptor.fec_size);
125 
126     f->data_size = hashtree_descriptor.fec_offset;
127 
128     f->ecc.blocks = fec_div_round_up(f->data_size, FEC_BLOCKSIZE);
129     f->ecc.rounds = fec_div_round_up(f->ecc.blocks, f->ecc.rsn);
130     f->ecc.size = hashtree_descriptor.fec_size;
131     f->ecc.start = hashtree_descriptor.fec_offset;
132     // TODO(xunchang) verify the integrity of the ecc data.
133     f->ecc.valid = true;
134 
135     std::string hash_algorithm =
136         reinterpret_cast<char *>(hashtree_descriptor.hash_algorithm);
137     int nid = -1;
138     if (android::base::EqualsIgnoreCase(hash_algorithm, "sha1")) {
139         nid = NID_sha1;
140     } else if (android::base::EqualsIgnoreCase(hash_algorithm, "sha256")) {
141         nid = NID_sha256;
142     } else {
143         error("unsupported hash algorithm %s", hash_algorithm.c_str());
144     }
145 
146     hashtree_info hashtree;
147     hashtree.initialize(hashtree_descriptor.tree_offset,
148                         hashtree_descriptor.tree_offset / FEC_BLOCKSIZE, salt,
149                         nid);
150     if (hashtree.verify_tree(f, root_hash.data()) != 0) {
151         error("failed to verify hashtree");
152         return -1;
153     }
154 
155     // We have validate the hashtree,
156     f->data_size = hashtree.hash_start;
157     f->avb = {
158         .valid = true,
159         .vbmeta = vbmeta,
160         .hashtree = std::move(hashtree),
161     };
162 
163     return 0;
164 }
165