1 /*
2 * Copyright (C) 2021 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 #include "ramdisk_utils.h"
17
18 #include <android-base/file.h>
19 #include <android-base/result.h>
20 #include <bootimg.h>
21
22 #include "cpio.h"
23 #include "lz4_legacy.h"
24
25 using android::base::ErrnoError;
26 using android::base::Error;
27 using android::base::ReadFullyAtOffset;
28 using android::base::WriteStringToFd;
29
30 namespace android {
31
32 namespace {
33 // Extract ramdisk from boot image / partition at |boot_path|.
34 // Return a temporary file storing the ramdisk section.
ExtractRamdiskRaw(std::string_view boot_path)35 android::base::Result<std::unique_ptr<TemporaryFile>> ExtractRamdiskRaw(
36 std::string_view boot_path) {
37 android::base::unique_fd bootimg(
38 TEMP_FAILURE_RETRY(open(boot_path.data(), O_RDONLY)));
39 if (!bootimg.ok()) return ErrnoError() << "open(" << boot_path << ")";
40 boot_img_hdr_v3 hdr;
41 if (!ReadFullyAtOffset(bootimg.get(), &hdr, sizeof(hdr), 0))
42 return ErrnoError() << "read header";
43 if (0 != memcmp(hdr.magic, BOOT_MAGIC, BOOT_MAGIC_SIZE))
44 return Error() << "Boot magic mismatch";
45
46 if (hdr.header_version < 3)
47 return Error() << "Unsupported header version V" << hdr.header_version;
48
49 // See bootimg.h
50 auto kernel_size_bytes = (hdr.kernel_size + 4096 - 1) / 4096 * 4096;
51 auto ramdisk_offset = 4096 + kernel_size_bytes;
52
53 std::string ramdisk_content(hdr.ramdisk_size, '\0');
54 if (!ReadFullyAtOffset(bootimg.get(), ramdisk_content.data(),
55 hdr.ramdisk_size, ramdisk_offset))
56 return ErrnoError() << "read ramdisk section";
57
58 auto ramdisk_content_file = std::make_unique<TemporaryFile>();
59 if (!WriteStringToFd(ramdisk_content, ramdisk_content_file->fd))
60 return ErrnoError() << "write ramdisk section to file";
61
62 return ramdisk_content_file;
63 }
64
65 } // namespace
66
67 // From the boot image / partition, extract the ramdisk section, decompress it,
68 // and extract from the cpio archive.
ExtractRamdiskToDirectory(std::string_view boot_path)69 android::base::Result<std::unique_ptr<TemporaryDir>> ExtractRamdiskToDirectory(
70 std::string_view boot_path) {
71 auto raw_ramdisk_file = ExtractRamdiskRaw(boot_path);
72 if (!raw_ramdisk_file.ok()) return raw_ramdisk_file.error();
73
74 TemporaryFile decompressed;
75 auto decompress_res = android::Lz4DecompressLegacy((*raw_ramdisk_file)->path,
76 decompressed.path);
77 if (!decompress_res.ok()) return decompress_res.error();
78
79 return android::CpioExtract(decompressed.path);
80 }
81
82 } // namespace android
83