2 * Copyright (C) 2016 The Android Open Source Project
4 * SPDX-License-Identifier: MIT
7 #if !defined(AVB_INSIDE_LIBAVB_H) && !defined(AVB_COMPILATION)
8 #error "Never include this file directly, include libavb.h instead."
11 #ifndef AVB_VBMETA_IMAGE_H_
12 #define AVB_VBMETA_IMAGE_H_
14 #include "avb_sysdeps.h"
20 #include "avb_crypto.h"
21 #include "avb_descriptor.h"
23 /* Size of the vbmeta image header. */
24 #define AVB_VBMETA_IMAGE_HEADER_SIZE 256
26 /* Magic for the vbmeta image header. */
27 #define AVB_MAGIC "AVB0"
28 #define AVB_MAGIC_LEN 4
30 /* Maximum size of the release string including the terminating NUL byte. */
31 #define AVB_RELEASE_STRING_SIZE 48
33 /* Flags for the vbmeta image.
35 * AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED: If this flag is set,
36 * hashtree image verification will be disabled.
38 * AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED: If this flag is set,
39 * verification will be disabled and descriptors will not be parsed.
42 AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED = (1 << 0),
43 AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED = (1 << 1)
44 } AvbVBMetaImageFlags;
46 /* Binary format for header of the vbmeta image.
48 * The vbmeta image consists of three blocks:
50 * +-----------------------------------------+
51 * | Header data - fixed size |
52 * +-----------------------------------------+
53 * | Authentication data - variable size |
54 * +-----------------------------------------+
55 * | Auxiliary data - variable size |
56 * +-----------------------------------------+
58 * The "Header data" block is described by this struct and is always
59 * |AVB_VBMETA_IMAGE_HEADER_SIZE| bytes long.
61 * The "Authentication data" block is |authentication_data_block_size|
62 * bytes long and contains the hash and signature used to authenticate
63 * the vbmeta image. The type of the hash and signature is defined by
64 * the |algorithm_type| field.
66 * The "Auxiliary data" is |auxiliary_data_block_size| bytes long and
67 * contains the auxiliary data including the public key used to make
68 * the signature and descriptors.
70 * The public key is at offset |public_key_offset| with size
71 * |public_key_size| in this block. The size of the public key data is
72 * defined by the |algorithm_type| field. The format of the public key
73 * data is described in the |AvbRSAPublicKeyHeader| struct.
75 * The descriptors starts at |descriptors_offset| from the beginning
76 * of the "Auxiliary Data" block and take up |descriptors_size|
77 * bytes. Each descriptor is stored as a |AvbDescriptor| with tag and
78 * number of bytes following. The number of descriptors can be
79 * determined by walking this data until |descriptors_size| is
82 * The size of each of the "Authentication data" and "Auxiliary data"
83 * blocks must be divisible by 64. This is to ensure proper alignment.
85 * Descriptors are free-form blocks stored in a part of the vbmeta
86 * image subject to the same integrity checks as the rest of the
87 * image. See the documentation for |AvbDescriptor| for well-known
88 * descriptors. See avb_descriptor_foreach() for a convenience
89 * function to iterate over descriptors.
91 * This struct is versioned, see the |required_libavb_version_major|
92 * and |required_libavb_version_minor| fields. This represents the
93 * minimum version of libavb required to verify the header and depends
94 * on the features (e.g. algorithms, descriptors) used. Note that this
95 * may be 1.0 even if generated by an avbtool from 1.4 but where no
96 * features introduced after 1.0 has been used. See the "Versioning
97 * and compatibility" section in the README.md file for more details.
99 * All fields are stored in network byte order when serialized. To
100 * generate a copy with fields swapped to native byte order, use the
101 * function avb_vbmeta_image_header_to_host_byte_order().
103 * Before reading and/or using any of this data, you MUST verify it
104 * using avb_vbmeta_image_verify() and reject it unless it's signed by
105 * a known good public key.
107 typedef struct AvbVBMetaImageHeader {
108 /* 0: Four bytes equal to "AVB0" (AVB_MAGIC). */
109 uint8_t magic[AVB_MAGIC_LEN];
111 /* 4: The major version of libavb required for this header. */
112 uint32_t required_libavb_version_major;
113 /* 8: The minor version of libavb required for this header. */
114 uint32_t required_libavb_version_minor;
116 /* 12: The size of the signature block. */
117 uint64_t authentication_data_block_size;
118 /* 20: The size of the auxiliary data block. */
119 uint64_t auxiliary_data_block_size;
121 /* 28: The verification algorithm used, see |AvbAlgorithmType| enum. */
122 uint32_t algorithm_type;
124 /* 32: Offset into the "Authentication data" block of hash data. */
125 uint64_t hash_offset;
126 /* 40: Length of the hash data. */
129 /* 48: Offset into the "Authentication data" block of signature data. */
130 uint64_t signature_offset;
131 /* 56: Length of the signature data. */
132 uint64_t signature_size;
134 /* 64: Offset into the "Auxiliary data" block of public key data. */
135 uint64_t public_key_offset;
136 /* 72: Length of the public key data. */
137 uint64_t public_key_size;
139 /* 80: Offset into the "Auxiliary data" block of public key metadata. */
140 uint64_t public_key_metadata_offset;
141 /* 88: Length of the public key metadata. Must be set to zero if there
142 * is no public key metadata.
144 uint64_t public_key_metadata_size;
146 /* 96: Offset into the "Auxiliary data" block of descriptor data. */
147 uint64_t descriptors_offset;
148 /* 104: Length of descriptor data. */
149 uint64_t descriptors_size;
151 /* 112: The rollback index which can be used to prevent rollback to
154 uint64_t rollback_index;
156 /* 120: Flags from the AvbVBMetaImageFlags enumeration. This must be
157 * set to zero if the vbmeta image is not a top-level image.
161 /* 124: Reserved to ensure |release_string| start on a 16-byte
162 * boundary. Must be set to zeroes.
164 uint8_t reserved0[4];
166 /* 128: The release string from avbtool, e.g. "avbtool 1.0.0" or
167 * "avbtool 1.0.0 xyz_board Git-234abde89". Is guaranteed to be NUL
168 * terminated. Applications must not make assumptions about how this
169 * string is formatted.
171 uint8_t release_string[AVB_RELEASE_STRING_SIZE];
173 /* 176: Padding to ensure struct is size AVB_VBMETA_IMAGE_HEADER_SIZE
174 * bytes. This must be set to zeroes.
176 uint8_t reserved[80];
177 } AVB_ATTR_PACKED AvbVBMetaImageHeader;
179 /* Copies |src| to |dest|, byte-swapping fields in the process.
181 * Make sure you've verified |src| using avb_vbmeta_image_verify()
182 * before accessing the data and/or using this function.
184 void avb_vbmeta_image_header_to_host_byte_order(const AvbVBMetaImageHeader* src,
185 AvbVBMetaImageHeader* dest);
187 /* Return codes used in avb_vbmeta_image_verify().
189 * AVB_VBMETA_VERIFY_RESULT_OK is returned if the vbmeta image header
190 * is valid, the hash is correct and the signature is correct. Keep in
191 * mind that you still need to check that you know the public key used
192 * to sign the image, see avb_vbmeta_image_verify() for details.
194 * AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED is returned if the vbmeta
195 * image header is valid but there is no signature or hash.
197 * AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER is returned if the
198 * header of the vbmeta image is invalid, for example, invalid magic
199 * or inconsistent data.
201 * AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION is returned if a) the
202 * vbmeta image requires a minimum version of libavb which exceeds the
203 * version of libavb used; or b) the vbmeta image major version
204 * differs from the major version of libavb in use.
206 * AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH is returned if the hash
207 * stored in the "Authentication data" block does not match the
210 * AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH is returned if the
211 * signature stored in the "Authentication data" block is invalid or
212 * doesn't match the public key stored in the vbmeta image.
215 AVB_VBMETA_VERIFY_RESULT_OK,
216 AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED,
217 AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER,
218 AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION,
219 AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH,
220 AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH,
221 } AvbVBMetaVerifyResult;
223 /* Get a textual representation of |result|. */
224 const char* avb_vbmeta_verify_result_to_string(AvbVBMetaVerifyResult result);
226 /* Checks that vbmeta image at |data| of size |length| is a valid
227 * vbmeta image. The complete contents of the vbmeta image must be
228 * passed in. It's fine if |length| is bigger than the actual image,
229 * typically callers of this function will load the entire contents of
230 * the 'vbmeta_a' or 'vbmeta_b' partition and pass in its length (for
233 * See the |AvbVBMetaImageHeader| struct for information about the
234 * three blocks (header, authentication, auxiliary) that make up a
237 * If the function returns |AVB_VBMETA_VERIFY_RESULT_OK| and
238 * |out_public_key_data| is non-NULL, it will be set to point inside
239 * |data| for where the serialized public key data is stored and
240 * |out_public_key_length|, if non-NULL, will be set to the length of
241 * the public key data. If there is no public key in the metadata then
242 * |out_public_key_data| is set to NULL.
244 * See the |AvbVBMetaVerifyResult| enum for possible return values.
248 * 1. Even if |AVB_VBMETA_VERIFY_RESULT_OK| is returned, you still
249 * need to check that the public key embedded in the image
250 * matches a known key! You can use 'avbtool extract_public_key'
251 * to extract the key (at build time, then store it along your
252 * code) and compare it to what is returned in
253 * |out_public_key_data|.
255 * 2. You need to check the |rollback_index| field against a stored
256 * value in NVRAM and reject the vbmeta image if the value in
257 * NVRAM is bigger than |rollback_index|. You must also update
258 * the value stored in NVRAM to the smallest value of
259 * |rollback_index| field from boot images in all bootable and
260 * authentic slots marked as GOOD.
262 * This is a low-level function to only verify the vbmeta data - you
263 * are likely looking for avb_slot_verify() instead for verifying
264 * integrity data for a whole set of partitions.
266 AvbVBMetaVerifyResult avb_vbmeta_image_verify(
269 const uint8_t** out_public_key_data,
270 size_t* out_public_key_length) AVB_ATTR_WARN_UNUSED_RESULT;
276 #endif /* AVB_VBMETA_IMAGE_H_ */