1 /* SPDX-License-Identifier: MIT */
3 * Copyright (C) 2016 The Android Open Source Project
6 #if !defined(AVB_INSIDE_LIBAVB_H) && !defined(AVB_COMPILATION)
7 #error "Never include this file directly, include libavb.h instead."
10 #ifndef AVB_VBMETA_IMAGE_H_
11 #define AVB_VBMETA_IMAGE_H_
13 #include "avb_sysdeps.h"
19 #include "avb_crypto.h"
20 #include "avb_descriptor.h"
22 /* Size of the vbmeta image header. */
23 #define AVB_VBMETA_IMAGE_HEADER_SIZE 256
25 /* Magic for the vbmeta image header. */
26 #define AVB_MAGIC "AVB0"
27 #define AVB_MAGIC_LEN 4
29 /* Maximum size of the release string including the terminating NUL byte. */
30 #define AVB_RELEASE_STRING_SIZE 48
32 /* Flags for the vbmeta image.
34 * AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED: If this flag is set,
35 * hashtree image verification will be disabled.
37 * AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED: If this flag is set,
38 * verification will be disabled and descriptors will not be parsed.
41 AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED = (1 << 0),
42 AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED = (1 << 1)
43 } AvbVBMetaImageFlags;
45 /* Binary format for header of the vbmeta image.
47 * The vbmeta image consists of three blocks:
49 * +-----------------------------------------+
50 * | Header data - fixed size |
51 * +-----------------------------------------+
52 * | Authentication data - variable size |
53 * +-----------------------------------------+
54 * | Auxiliary data - variable size |
55 * +-----------------------------------------+
57 * The "Header data" block is described by this struct and is always
58 * |AVB_VBMETA_IMAGE_HEADER_SIZE| bytes long.
60 * The "Authentication data" block is |authentication_data_block_size|
61 * bytes long and contains the hash and signature used to authenticate
62 * the vbmeta image. The type of the hash and signature is defined by
63 * the |algorithm_type| field.
65 * The "Auxiliary data" is |auxiliary_data_block_size| bytes long and
66 * contains the auxiliary data including the public key used to make
67 * the signature and descriptors.
69 * The public key is at offset |public_key_offset| with size
70 * |public_key_size| in this block. The size of the public key data is
71 * defined by the |algorithm_type| field. The format of the public key
72 * data is described in the |AvbRSAPublicKeyHeader| struct.
74 * The descriptors starts at |descriptors_offset| from the beginning
75 * of the "Auxiliary Data" block and take up |descriptors_size|
76 * bytes. Each descriptor is stored as a |AvbDescriptor| with tag and
77 * number of bytes following. The number of descriptors can be
78 * determined by walking this data until |descriptors_size| is
81 * The size of each of the "Authentication data" and "Auxiliary data"
82 * blocks must be divisible by 64. This is to ensure proper alignment.
84 * Descriptors are free-form blocks stored in a part of the vbmeta
85 * image subject to the same integrity checks as the rest of the
86 * image. See the documentation for |AvbDescriptor| for well-known
87 * descriptors. See avb_descriptor_foreach() for a convenience
88 * function to iterate over descriptors.
90 * This struct is versioned, see the |required_libavb_version_major|
91 * and |required_libavb_version_minor| fields. This represents the
92 * minimum version of libavb required to verify the header and depends
93 * on the features (e.g. algorithms, descriptors) used. Note that this
94 * may be 1.0 even if generated by an avbtool from 1.4 but where no
95 * features introduced after 1.0 has been used. See the "Versioning
96 * and compatibility" section in the README.md file for more details.
98 * All fields are stored in network byte order when serialized. To
99 * generate a copy with fields swapped to native byte order, use the
100 * function avb_vbmeta_image_header_to_host_byte_order().
102 * Before reading and/or using any of this data, you MUST verify it
103 * using avb_vbmeta_image_verify() and reject it unless it's signed by
104 * a known good public key.
106 typedef struct AvbVBMetaImageHeader {
107 /* 0: Four bytes equal to "AVB0" (AVB_MAGIC). */
108 uint8_t magic[AVB_MAGIC_LEN];
110 /* 4: The major version of libavb required for this header. */
111 uint32_t required_libavb_version_major;
112 /* 8: The minor version of libavb required for this header. */
113 uint32_t required_libavb_version_minor;
115 /* 12: The size of the signature block. */
116 uint64_t authentication_data_block_size;
117 /* 20: The size of the auxiliary data block. */
118 uint64_t auxiliary_data_block_size;
120 /* 28: The verification algorithm used, see |AvbAlgorithmType| enum. */
121 uint32_t algorithm_type;
123 /* 32: Offset into the "Authentication data" block of hash data. */
124 uint64_t hash_offset;
125 /* 40: Length of the hash data. */
128 /* 48: Offset into the "Authentication data" block of signature data. */
129 uint64_t signature_offset;
130 /* 56: Length of the signature data. */
131 uint64_t signature_size;
133 /* 64: Offset into the "Auxiliary data" block of public key data. */
134 uint64_t public_key_offset;
135 /* 72: Length of the public key data. */
136 uint64_t public_key_size;
138 /* 80: Offset into the "Auxiliary data" block of public key metadata. */
139 uint64_t public_key_metadata_offset;
140 /* 88: Length of the public key metadata. Must be set to zero if there
141 * is no public key metadata.
143 uint64_t public_key_metadata_size;
145 /* 96: Offset into the "Auxiliary data" block of descriptor data. */
146 uint64_t descriptors_offset;
147 /* 104: Length of descriptor data. */
148 uint64_t descriptors_size;
150 /* 112: The rollback index which can be used to prevent rollback to
153 uint64_t rollback_index;
155 /* 120: Flags from the AvbVBMetaImageFlags enumeration. This must be
156 * set to zero if the vbmeta image is not a top-level image.
160 /* 124: Reserved to ensure |release_string| start on a 16-byte
161 * boundary. Must be set to zeroes.
163 uint8_t reserved0[4];
165 /* 128: The release string from avbtool, e.g. "avbtool 1.0.0" or
166 * "avbtool 1.0.0 xyz_board Git-234abde89". Is guaranteed to be NUL
167 * terminated. Applications must not make assumptions about how this
168 * string is formatted.
170 uint8_t release_string[AVB_RELEASE_STRING_SIZE];
172 /* 176: Padding to ensure struct is size AVB_VBMETA_IMAGE_HEADER_SIZE
173 * bytes. This must be set to zeroes.
175 uint8_t reserved[80];
176 } AVB_ATTR_PACKED AvbVBMetaImageHeader;
178 /* Copies |src| to |dest|, byte-swapping fields in the process.
180 * Make sure you've verified |src| using avb_vbmeta_image_verify()
181 * before accessing the data and/or using this function.
183 void avb_vbmeta_image_header_to_host_byte_order(const AvbVBMetaImageHeader* src,
184 AvbVBMetaImageHeader* dest);
186 /* Return codes used in avb_vbmeta_image_verify().
188 * AVB_VBMETA_VERIFY_RESULT_OK is returned if the vbmeta image header
189 * is valid, the hash is correct and the signature is correct. Keep in
190 * mind that you still need to check that you know the public key used
191 * to sign the image, see avb_vbmeta_image_verify() for details.
193 * AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED is returned if the vbmeta
194 * image header is valid but there is no signature or hash.
196 * AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER is returned if the
197 * header of the vbmeta image is invalid, for example, invalid magic
198 * or inconsistent data.
200 * AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION is returned if a) the
201 * vbmeta image requires a minimum version of libavb which exceeds the
202 * version of libavb used; or b) the vbmeta image major version
203 * differs from the major version of libavb in use.
205 * AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH is returned if the hash
206 * stored in the "Authentication data" block does not match the
209 * AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH is returned if the
210 * signature stored in the "Authentication data" block is invalid or
211 * doesn't match the public key stored in the vbmeta image.
214 AVB_VBMETA_VERIFY_RESULT_OK,
215 AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED,
216 AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER,
217 AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION,
218 AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH,
219 AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH,
220 } AvbVBMetaVerifyResult;
222 /* Get a textual representation of |result|. */
223 const char* avb_vbmeta_verify_result_to_string(AvbVBMetaVerifyResult result);
225 /* Checks that vbmeta image at |data| of size |length| is a valid
226 * vbmeta image. The complete contents of the vbmeta image must be
227 * passed in. It's fine if |length| is bigger than the actual image,
228 * typically callers of this function will load the entire contents of
229 * the 'vbmeta_a' or 'vbmeta_b' partition and pass in its length (for
232 * See the |AvbVBMetaImageHeader| struct for information about the
233 * three blocks (header, authentication, auxiliary) that make up a
236 * If the function returns |AVB_VBMETA_VERIFY_RESULT_OK| and
237 * |out_public_key_data| is non-NULL, it will be set to point inside
238 * |data| for where the serialized public key data is stored and
239 * |out_public_key_length|, if non-NULL, will be set to the length of
240 * the public key data. If there is no public key in the metadata then
241 * |out_public_key_data| is set to NULL.
243 * See the |AvbVBMetaVerifyResult| enum for possible return values.
247 * 1. Even if |AVB_VBMETA_VERIFY_RESULT_OK| is returned, you still
248 * need to check that the public key embedded in the image
249 * matches a known key! You can use 'avbtool extract_public_key'
250 * to extract the key (at build time, then store it along your
251 * code) and compare it to what is returned in
252 * |out_public_key_data|.
254 * 2. You need to check the |rollback_index| field against a stored
255 * value in NVRAM and reject the vbmeta image if the value in
256 * NVRAM is bigger than |rollback_index|. You must also update
257 * the value stored in NVRAM to the smallest value of
258 * |rollback_index| field from boot images in all bootable and
259 * authentic slots marked as GOOD.
261 * This is a low-level function to only verify the vbmeta data - you
262 * are likely looking for avb_slot_verify() instead for verifying
263 * integrity data for a whole set of partitions.
265 AvbVBMetaVerifyResult avb_vbmeta_image_verify(
268 const uint8_t** out_public_key_data,
269 size_t* out_public_key_length) AVB_ATTR_WARN_UNUSED_RESULT;
275 #endif /* AVB_VBMETA_IMAGE_H_ */