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275 lines
10 KiB
C
275 lines
10 KiB
C
/* SPDX-License-Identifier: MIT */
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/*
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* Copyright (C) 2016 The Android Open Source Project
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*/
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#if !defined(AVB_INSIDE_LIBAVB_H) && !defined(AVB_COMPILATION)
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#error "Never include this file directly, include libavb.h instead."
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#endif
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#ifndef AVB_VBMETA_IMAGE_H_
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#define AVB_VBMETA_IMAGE_H_
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#include "avb_sysdeps.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include "avb_crypto.h"
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#include "avb_descriptor.h"
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/* Size of the vbmeta image header. */
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#define AVB_VBMETA_IMAGE_HEADER_SIZE 256
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/* Magic for the vbmeta image header. */
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#define AVB_MAGIC "AVB0"
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#define AVB_MAGIC_LEN 4
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/* Maximum size of the release string including the terminating NUL byte. */
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#define AVB_RELEASE_STRING_SIZE 48
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/* Flags for the vbmeta image.
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*
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* AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED: If this flag is set,
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* hashtree image verification will be disabled.
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*
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* AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED: If this flag is set,
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* verification will be disabled and descriptors will not be parsed.
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*/
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typedef enum {
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AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED = (1 << 0),
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AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED = (1 << 1)
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} AvbVBMetaImageFlags;
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/* Binary format for header of the vbmeta image.
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*
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* The vbmeta image consists of three blocks:
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*
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* +-----------------------------------------+
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* | Header data - fixed size |
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* +-----------------------------------------+
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* | Authentication data - variable size |
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* +-----------------------------------------+
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* | Auxiliary data - variable size |
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* +-----------------------------------------+
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*
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* The "Header data" block is described by this struct and is always
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* |AVB_VBMETA_IMAGE_HEADER_SIZE| bytes long.
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*
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* The "Authentication data" block is |authentication_data_block_size|
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* bytes long and contains the hash and signature used to authenticate
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* the vbmeta image. The type of the hash and signature is defined by
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* the |algorithm_type| field.
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*
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* The "Auxiliary data" is |auxiliary_data_block_size| bytes long and
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* contains the auxiliary data including the public key used to make
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* the signature and descriptors.
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*
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* The public key is at offset |public_key_offset| with size
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* |public_key_size| in this block. The size of the public key data is
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* defined by the |algorithm_type| field. The format of the public key
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* data is described in the |AvbRSAPublicKeyHeader| struct.
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*
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* The descriptors starts at |descriptors_offset| from the beginning
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* of the "Auxiliary Data" block and take up |descriptors_size|
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* bytes. Each descriptor is stored as a |AvbDescriptor| with tag and
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* number of bytes following. The number of descriptors can be
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* determined by walking this data until |descriptors_size| is
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* exhausted.
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*
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* The size of each of the "Authentication data" and "Auxiliary data"
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* blocks must be divisible by 64. This is to ensure proper alignment.
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*
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* Descriptors are free-form blocks stored in a part of the vbmeta
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* image subject to the same integrity checks as the rest of the
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* image. See the documentation for |AvbDescriptor| for well-known
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* descriptors. See avb_descriptor_foreach() for a convenience
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* function to iterate over descriptors.
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*
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* This struct is versioned, see the |required_libavb_version_major|
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* and |required_libavb_version_minor| fields. This represents the
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* minimum version of libavb required to verify the header and depends
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* on the features (e.g. algorithms, descriptors) used. Note that this
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* may be 1.0 even if generated by an avbtool from 1.4 but where no
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* features introduced after 1.0 has been used. See the "Versioning
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* and compatibility" section in the README.md file for more details.
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*
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* All fields are stored in network byte order when serialized. To
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* generate a copy with fields swapped to native byte order, use the
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* function avb_vbmeta_image_header_to_host_byte_order().
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*
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* Before reading and/or using any of this data, you MUST verify it
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* using avb_vbmeta_image_verify() and reject it unless it's signed by
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* a known good public key.
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*/
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typedef struct AvbVBMetaImageHeader {
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/* 0: Four bytes equal to "AVB0" (AVB_MAGIC). */
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uint8_t magic[AVB_MAGIC_LEN];
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/* 4: The major version of libavb required for this header. */
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uint32_t required_libavb_version_major;
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/* 8: The minor version of libavb required for this header. */
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uint32_t required_libavb_version_minor;
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/* 12: The size of the signature block. */
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uint64_t authentication_data_block_size;
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/* 20: The size of the auxiliary data block. */
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uint64_t auxiliary_data_block_size;
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/* 28: The verification algorithm used, see |AvbAlgorithmType| enum. */
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uint32_t algorithm_type;
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/* 32: Offset into the "Authentication data" block of hash data. */
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uint64_t hash_offset;
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/* 40: Length of the hash data. */
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uint64_t hash_size;
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/* 48: Offset into the "Authentication data" block of signature data. */
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uint64_t signature_offset;
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/* 56: Length of the signature data. */
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uint64_t signature_size;
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/* 64: Offset into the "Auxiliary data" block of public key data. */
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uint64_t public_key_offset;
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/* 72: Length of the public key data. */
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uint64_t public_key_size;
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/* 80: Offset into the "Auxiliary data" block of public key metadata. */
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uint64_t public_key_metadata_offset;
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/* 88: Length of the public key metadata. Must be set to zero if there
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* is no public key metadata.
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*/
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uint64_t public_key_metadata_size;
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/* 96: Offset into the "Auxiliary data" block of descriptor data. */
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uint64_t descriptors_offset;
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/* 104: Length of descriptor data. */
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uint64_t descriptors_size;
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/* 112: The rollback index which can be used to prevent rollback to
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* older versions.
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*/
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uint64_t rollback_index;
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/* 120: Flags from the AvbVBMetaImageFlags enumeration. This must be
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* set to zero if the vbmeta image is not a top-level image.
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*/
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uint32_t flags;
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/* 124: Reserved to ensure |release_string| start on a 16-byte
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* boundary. Must be set to zeroes.
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*/
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uint8_t reserved0[4];
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/* 128: The release string from avbtool, e.g. "avbtool 1.0.0" or
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* "avbtool 1.0.0 xyz_board Git-234abde89". Is guaranteed to be NUL
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* terminated. Applications must not make assumptions about how this
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* string is formatted.
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*/
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uint8_t release_string[AVB_RELEASE_STRING_SIZE];
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/* 176: Padding to ensure struct is size AVB_VBMETA_IMAGE_HEADER_SIZE
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* bytes. This must be set to zeroes.
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*/
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uint8_t reserved[80];
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} AVB_ATTR_PACKED AvbVBMetaImageHeader;
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/* Copies |src| to |dest|, byte-swapping fields in the process.
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*
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* Make sure you've verified |src| using avb_vbmeta_image_verify()
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* before accessing the data and/or using this function.
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*/
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void avb_vbmeta_image_header_to_host_byte_order(const AvbVBMetaImageHeader* src,
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AvbVBMetaImageHeader* dest);
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/* Return codes used in avb_vbmeta_image_verify().
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*
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* AVB_VBMETA_VERIFY_RESULT_OK is returned if the vbmeta image header
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* is valid, the hash is correct and the signature is correct. Keep in
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* mind that you still need to check that you know the public key used
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* to sign the image, see avb_vbmeta_image_verify() for details.
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*
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* AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED is returned if the vbmeta
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* image header is valid but there is no signature or hash.
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*
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* AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER is returned if the
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* header of the vbmeta image is invalid, for example, invalid magic
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* or inconsistent data.
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*
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* AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION is returned if a) the
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* vbmeta image requires a minimum version of libavb which exceeds the
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* version of libavb used; or b) the vbmeta image major version
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* differs from the major version of libavb in use.
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*
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* AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH is returned if the hash
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* stored in the "Authentication data" block does not match the
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* calculated hash.
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*
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* AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH is returned if the
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* signature stored in the "Authentication data" block is invalid or
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* doesn't match the public key stored in the vbmeta image.
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*/
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typedef enum {
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AVB_VBMETA_VERIFY_RESULT_OK,
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AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED,
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AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER,
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AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION,
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AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH,
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AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH,
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} AvbVBMetaVerifyResult;
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/* Get a textual representation of |result|. */
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const char* avb_vbmeta_verify_result_to_string(AvbVBMetaVerifyResult result);
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/* Checks that vbmeta image at |data| of size |length| is a valid
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* vbmeta image. The complete contents of the vbmeta image must be
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* passed in. It's fine if |length| is bigger than the actual image,
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* typically callers of this function will load the entire contents of
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* the 'vbmeta_a' or 'vbmeta_b' partition and pass in its length (for
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* example, 1 MiB).
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*
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* See the |AvbVBMetaImageHeader| struct for information about the
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* three blocks (header, authentication, auxiliary) that make up a
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* vbmeta image.
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*
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* If the function returns |AVB_VBMETA_VERIFY_RESULT_OK| and
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* |out_public_key_data| is non-NULL, it will be set to point inside
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* |data| for where the serialized public key data is stored and
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* |out_public_key_length|, if non-NULL, will be set to the length of
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* the public key data. If there is no public key in the metadata then
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* |out_public_key_data| is set to NULL.
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*
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* See the |AvbVBMetaVerifyResult| enum for possible return values.
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*
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* VERY IMPORTANT:
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*
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* 1. Even if |AVB_VBMETA_VERIFY_RESULT_OK| is returned, you still
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* need to check that the public key embedded in the image
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* matches a known key! You can use 'avbtool extract_public_key'
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* to extract the key (at build time, then store it along your
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* code) and compare it to what is returned in
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* |out_public_key_data|.
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*
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* 2. You need to check the |rollback_index| field against a stored
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* value in NVRAM and reject the vbmeta image if the value in
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* NVRAM is bigger than |rollback_index|. You must also update
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* the value stored in NVRAM to the smallest value of
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* |rollback_index| field from boot images in all bootable and
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* authentic slots marked as GOOD.
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*
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* This is a low-level function to only verify the vbmeta data - you
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* are likely looking for avb_slot_verify() instead for verifying
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* integrity data for a whole set of partitions.
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*/
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AvbVBMetaVerifyResult avb_vbmeta_image_verify(
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const uint8_t* data,
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size_t length,
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const uint8_t** out_public_key_data,
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size_t* out_public_key_length) AVB_ATTR_WARN_UNUSED_RESULT;
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#ifdef __cplusplus
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}
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#endif
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#endif /* AVB_VBMETA_IMAGE_H_ */
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