1 /* SPDX-License-Identifier: MIT */ 2 /* 3 * Copyright (C) 2016 The Android Open Source Project 4 */ 5 6 #if !defined(AVB_INSIDE_LIBAVB_H) && !defined(AVB_COMPILATION) 7 #error "Never include this file directly, include libavb.h instead." 8 #endif 9 10 #ifndef AVB_VBMETA_IMAGE_H_ 11 #define AVB_VBMETA_IMAGE_H_ 12 13 #include "avb_sysdeps.h" 14 15 #ifdef __cplusplus 16 extern "C" { 17 #endif 18 19 #include "avb_crypto.h" 20 #include "avb_descriptor.h" 21 22 /* Size of the vbmeta image header. */ 23 #define AVB_VBMETA_IMAGE_HEADER_SIZE 256 24 25 /* Magic for the vbmeta image header. */ 26 #define AVB_MAGIC "AVB0" 27 #define AVB_MAGIC_LEN 4 28 29 /* Maximum size of the release string including the terminating NUL byte. */ 30 #define AVB_RELEASE_STRING_SIZE 48 31 32 /* Flags for the vbmeta image. 33 * 34 * AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED: If this flag is set, 35 * hashtree image verification will be disabled. 36 * 37 * AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED: If this flag is set, 38 * verification will be disabled and descriptors will not be parsed. 39 */ 40 typedef enum { 41 AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED = (1 << 0), 42 AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED = (1 << 1) 43 } AvbVBMetaImageFlags; 44 45 /* Binary format for header of the vbmeta image. 46 * 47 * The vbmeta image consists of three blocks: 48 * 49 * +-----------------------------------------+ 50 * | Header data - fixed size | 51 * +-----------------------------------------+ 52 * | Authentication data - variable size | 53 * +-----------------------------------------+ 54 * | Auxiliary data - variable size | 55 * +-----------------------------------------+ 56 * 57 * The "Header data" block is described by this struct and is always 58 * |AVB_VBMETA_IMAGE_HEADER_SIZE| bytes long. 59 * 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. 64 * 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. 68 * 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. 73 * 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 79 * exhausted. 80 * 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. 83 * 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. 89 * 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. 97 * 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(). 101 * 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. 105 */ 106 typedef struct AvbVBMetaImageHeader { 107 /* 0: Four bytes equal to "AVB0" (AVB_MAGIC). */ 108 uint8_t magic[AVB_MAGIC_LEN]; 109 110 /* 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; 114 115 /* 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; 119 120 /* 28: The verification algorithm used, see |AvbAlgorithmType| enum. */ 121 uint32_t algorithm_type; 122 123 /* 32: Offset into the "Authentication data" block of hash data. */ 124 uint64_t hash_offset; 125 /* 40: Length of the hash data. */ 126 uint64_t hash_size; 127 128 /* 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; 132 133 /* 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; 137 138 /* 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. 142 */ 143 uint64_t public_key_metadata_size; 144 145 /* 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; 149 150 /* 112: The rollback index which can be used to prevent rollback to 151 * older versions. 152 */ 153 uint64_t rollback_index; 154 155 /* 120: Flags from the AvbVBMetaImageFlags enumeration. This must be 156 * set to zero if the vbmeta image is not a top-level image. 157 */ 158 uint32_t flags; 159 160 /* 124: Reserved to ensure |release_string| start on a 16-byte 161 * boundary. Must be set to zeroes. 162 */ 163 uint8_t reserved0[4]; 164 165 /* 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. 169 */ 170 uint8_t release_string[AVB_RELEASE_STRING_SIZE]; 171 172 /* 176: Padding to ensure struct is size AVB_VBMETA_IMAGE_HEADER_SIZE 173 * bytes. This must be set to zeroes. 174 */ 175 uint8_t reserved[80]; 176 } AVB_ATTR_PACKED AvbVBMetaImageHeader; 177 178 /* Copies |src| to |dest|, byte-swapping fields in the process. 179 * 180 * Make sure you've verified |src| using avb_vbmeta_image_verify() 181 * before accessing the data and/or using this function. 182 */ 183 void avb_vbmeta_image_header_to_host_byte_order(const AvbVBMetaImageHeader* src, 184 AvbVBMetaImageHeader* dest); 185 186 /* Return codes used in avb_vbmeta_image_verify(). 187 * 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. 192 * 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. 195 * 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. 199 * 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. 204 * 205 * AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH is returned if the hash 206 * stored in the "Authentication data" block does not match the 207 * calculated hash. 208 * 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. 212 */ 213 typedef enum { 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; 221 222 /* Get a textual representation of |result|. */ 223 const char* avb_vbmeta_verify_result_to_string(AvbVBMetaVerifyResult result); 224 225 /* 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 230 * example, 1 MiB). 231 * 232 * See the |AvbVBMetaImageHeader| struct for information about the 233 * three blocks (header, authentication, auxiliary) that make up a 234 * vbmeta image. 235 * 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. 242 * 243 * See the |AvbVBMetaVerifyResult| enum for possible return values. 244 * 245 * VERY IMPORTANT: 246 * 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|. 253 * 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. 260 * 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. 264 */ 265 AvbVBMetaVerifyResult avb_vbmeta_image_verify( 266 const uint8_t* data, 267 size_t length, 268 const uint8_t** out_public_key_data, 269 size_t* out_public_key_length) AVB_ATTR_WARN_UNUSED_RESULT; 270 271 #ifdef __cplusplus 272 } 273 #endif 274 275 #endif /* AVB_VBMETA_IMAGE_H_ */ 276
