The tool avbtool (from AOSP) manipulates vbmeta images.
vbmeta (Verified Boot Metadata) is a critical data structure used in Android's Verified Boot (AVB) system. It cryptographically anchors the chain of trust from the bootloader to the operating system. The vbmeta partition (or image) stores integrity hashes and digital signatures for other partitions (e.g., boot , system , vendor ), ensuring that no unauthorized code or data has been tampered with before execution. vbmeta
| Field | Size (bytes) | Description | |-------|--------------|-------------| | magic | 4 | Constant AVB_MAGIC = "AVB0" | | version_major | 4 | AVB format major version (e.g., 1) | | version_minor | 4 | Minor version (e.g., 0) | | authentication_data_block_size | 8 | Size of signature + public key (if embedded) | | auxiliary_data_block_size | 8 | Size of descriptors, rollback index, etc. | | algorithm_type | 4 | Signing algorithm (e.g., SHA256_RSA2048) | | hash_tree_offset | 8 | Offset to hash tree (if used) | | rollback_index | 8 | Anti-rollback counter | | flags | 4 | e.g., AVB_FLAGS_VERIFICATION_DISABLED | | public_key (variable) | – | Embedded public key (optional) | | signature (variable) | – | Signature of the header + auxiliary data | The tool avbtool (from AOSP) manipulates vbmeta images
For those looking to install a custom ROM or root their device , vbmeta often becomes a hurdle. Because any modification to the system triggers a verification failure, users must often "disable" or "patch" vbmeta. Common Fastboot Commands The vbmeta partition (or image) stores integrity hashes
Device storage ├── bootloader (pre-verified by hardware) ├── vbmeta → Signs/hashes: boot, dtbo, (optionally system, vendor) ├── boot → Kernel + ramdisk ├── dtbo → Device tree overlay ├── vbmeta_system → Signs system partition ├── system → System image (hash tree) ├── vbmeta_vendor → Signs vendor partition └── vendor → Vendor image (hash tree)
fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img
When flashing a device using fastboot , developers use specific flags to bypass these checks: fastboot flash vbmeta vbmeta.img
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