| // Copyright 2021, The Android Open Source Project |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| //! Provides routines to read/write on the instance disk. |
| //! |
| //! Instance disk is a disk where the identity of a VM instance is recorded. The identity usually |
| //! includes certificates of the VM payload that is trusted, but not limited to it. Instance disk |
| //! is empty when a VM is first booted. The identity data is filled in during the first boot, and |
| //! then encrypted and signed. Subsequent boots decrypts and authenticates the data and uses the |
| //! identity data to further verify the payload (e.g. against the certificate). |
| //! |
| //! Instance disk consists of a disk header and one or more partitions each of which consists of a |
| //! header and payload. Each header (both the disk header and a partition header) is 512 bytes |
| //! long. Payload is just next to the header and its size can be arbitrary. Headers are located at |
| //! 512 bytes boundaries. So, when the size of a payload is not multiple of 512, there exists a gap |
| //! between the end of the payload and the start of the next partition (if there is any). |
| //! |
| //! Each partition is identified by a UUID. A partition is created for a program loader that |
| //! participates in the boot chain of the VM. Each program loader is expected to locate the |
| //! partition that corresponds to the loader using the UUID that is assigned to the loader. |
| //! |
| //! The payload of a partition is encrypted/signed by a key that is unique to the loader and to the |
| //! VM as well. Failing to decrypt/authenticate a partition by a loader stops the boot process. |
| |
| use crate::ioutil; |
| |
| use anyhow::{anyhow, bail, Context, Result}; |
| use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt}; |
| use dice_driver::DiceDriver; |
| use openssl::symm::{decrypt_aead, encrypt_aead, Cipher}; |
| use serde::{Deserialize, Serialize}; |
| use std::fs::{File, OpenOptions}; |
| use std::io::{Read, Seek, SeekFrom, Write}; |
| use uuid::Uuid; |
| |
| /// Path to the instance disk inside the VM |
| const INSTANCE_IMAGE_PATH: &str = "/dev/block/by-name/vm-instance"; |
| |
| /// Identifier for the key used to seal the instance data. |
| const INSTANCE_KEY_IDENTIFIER: &[u8] = b"microdroid_manager_key"; |
| |
| /// Magic string in the instance disk header |
| const DISK_HEADER_MAGIC: &str = "Android-VM-instance"; |
| |
| /// Version of the instance disk format |
| const DISK_HEADER_VERSION: u16 = 1; |
| |
| /// Size of the headers in the instance disk |
| const DISK_HEADER_SIZE: u64 = 512; |
| const PARTITION_HEADER_SIZE: u64 = 512; |
| |
| /// UUID of the partition that microdroid manager uses |
| const MICRODROID_PARTITION_UUID: &str = "cf9afe9a-0662-11ec-a329-c32663a09d75"; |
| |
| /// Size of the AES256-GCM tag |
| const AES_256_GCM_TAG_LENGTH: usize = 16; |
| |
| /// Size of the AES256-GCM nonce |
| const AES_256_GCM_NONCE_LENGTH: usize = 12; |
| |
| /// Handle to the instance disk |
| pub struct InstanceDisk { |
| file: File, |
| } |
| |
| /// Information from a partition header |
| struct PartitionHeader { |
| uuid: Uuid, |
| payload_size: u64, // in bytes |
| } |
| |
| /// Offset of a partition in the instance disk |
| type PartitionOffset = u64; |
| |
| impl InstanceDisk { |
| /// Creates handle to instance disk |
| pub fn new() -> Result<Self> { |
| let mut file = OpenOptions::new() |
| .read(true) |
| .write(true) |
| .open(INSTANCE_IMAGE_PATH) |
| .with_context(|| format!("Failed to open {}", INSTANCE_IMAGE_PATH))?; |
| |
| // Check if this file is a valid instance disk by examining the header (the first block) |
| let mut magic = [0; DISK_HEADER_MAGIC.len()]; |
| file.read_exact(&mut magic)?; |
| if magic != DISK_HEADER_MAGIC.as_bytes() { |
| bail!("invalid magic: {:?}", magic); |
| } |
| |
| let version = file.read_u16::<LittleEndian>()?; |
| if version == 0 { |
| bail!("invalid version: {}", version); |
| } |
| if version > DISK_HEADER_VERSION { |
| bail!("unsupported version: {}", version); |
| } |
| |
| Ok(Self { file }) |
| } |
| |
| /// Reads the identity data that was written by microdroid manager. The returned data is |
| /// plaintext, although it is stored encrypted. In case when the partition for microdroid |
| /// manager doesn't exist, which can happen if it's the first boot, `Ok(None)` is returned. |
| pub fn read_microdroid_data(&mut self, dice: &DiceDriver) -> Result<Option<MicrodroidData>> { |
| let (header, offset) = self.locate_microdroid_header()?; |
| if header.is_none() { |
| return Ok(None); |
| } |
| let header = header.unwrap(); |
| let payload_offset = offset + PARTITION_HEADER_SIZE; |
| self.file.seek(SeekFrom::Start(payload_offset))?; |
| |
| // Read the nonce (unencrypted) |
| let mut nonce = [0; AES_256_GCM_NONCE_LENGTH]; |
| self.file.read_exact(&mut nonce)?; |
| |
| // Read the encrypted payload |
| let payload_size = |
| header.payload_size as usize - AES_256_GCM_NONCE_LENGTH - AES_256_GCM_TAG_LENGTH; |
| let mut data = vec![0; payload_size]; |
| self.file.read_exact(&mut data)?; |
| |
| // Read the tag |
| let mut tag = [0; AES_256_GCM_TAG_LENGTH]; |
| self.file.read_exact(&mut tag)?; |
| |
| // Read the header as well because it's part of the signed data (though not encrypted). |
| let mut header = [0; PARTITION_HEADER_SIZE as usize]; |
| self.file.seek(SeekFrom::Start(offset))?; |
| self.file.read_exact(&mut header)?; |
| |
| // Decrypt and authenticate the data (along with the header). |
| let cipher = Cipher::aes_256_gcm(); |
| let key = dice.get_sealing_key(INSTANCE_KEY_IDENTIFIER, cipher.key_len())?; |
| let plaintext = decrypt_aead(cipher, &key, Some(&nonce), &header, &data, &tag)?; |
| |
| let microdroid_data = serde_cbor::from_slice(plaintext.as_slice())?; |
| Ok(Some(microdroid_data)) |
| } |
| |
| /// Writes identity data to the partition for microdroid manager. The partition is appended |
| /// if it doesn't exist. The data is stored encrypted. |
| pub fn write_microdroid_data( |
| &mut self, |
| microdroid_data: &MicrodroidData, |
| dice: &DiceDriver, |
| ) -> Result<()> { |
| let (header, offset) = self.locate_microdroid_header()?; |
| |
| let data = serde_cbor::to_vec(microdroid_data)?; |
| |
| // By encrypting and signing the data, tag will be appended. The tag also becomes part of |
| // the encrypted payload which will be written. In addition, a nonce will be prepended |
| // (non-encrypted). |
| let payload_size = (AES_256_GCM_NONCE_LENGTH + data.len() + AES_256_GCM_TAG_LENGTH) as u64; |
| |
| // If the partition exists, make sure we don't change the partition size. If not (i.e. |
| // partition is not found), write the header at the empty place. |
| if let Some(header) = header { |
| if header.payload_size != payload_size { |
| bail!("Can't change payload size from {} to {}", header.payload_size, payload_size); |
| } |
| } else { |
| let uuid = Uuid::parse_str(MICRODROID_PARTITION_UUID)?; |
| self.write_header_at(offset, &uuid, payload_size)?; |
| } |
| |
| // Read the header as it is used as additionally authenticated data (AAD). |
| let mut header = [0; PARTITION_HEADER_SIZE as usize]; |
| self.file.seek(SeekFrom::Start(offset))?; |
| self.file.read_exact(&mut header)?; |
| |
| // Generate a nonce randomly and recorde it on the disk first. |
| let nonce = rand::random::<[u8; AES_256_GCM_NONCE_LENGTH]>(); |
| self.file.seek(SeekFrom::Start(offset + PARTITION_HEADER_SIZE))?; |
| self.file.write_all(nonce.as_ref())?; |
| |
| // Then encrypt and sign the data. |
| let cipher = Cipher::aes_256_gcm(); |
| let key = dice.get_sealing_key(INSTANCE_KEY_IDENTIFIER, cipher.key_len())?; |
| let mut tag = [0; AES_256_GCM_TAG_LENGTH]; |
| let ciphertext = encrypt_aead(cipher, &key, Some(&nonce), &header, &data, &mut tag)?; |
| |
| // Persist the encrypted payload data and the tag. |
| self.file.write_all(&ciphertext)?; |
| self.file.write_all(&tag)?; |
| ioutil::blkflsbuf(&mut self.file)?; |
| |
| Ok(()) |
| } |
| |
| /// Read header at `header_offset` and parse it into a `PartitionHeader`. |
| fn read_header_at(&mut self, header_offset: u64) -> Result<PartitionHeader> { |
| assert!( |
| header_offset % PARTITION_HEADER_SIZE == 0, |
| "header offset {} is not aligned to 512 bytes", |
| header_offset |
| ); |
| |
| let mut uuid = [0; 16]; |
| self.file.seek(SeekFrom::Start(header_offset))?; |
| self.file.read_exact(&mut uuid)?; |
| let uuid = Uuid::from_bytes(uuid); |
| let payload_size = self.file.read_u64::<LittleEndian>()?; |
| |
| Ok(PartitionHeader { uuid, payload_size }) |
| } |
| |
| /// Write header at `header_offset` |
| fn write_header_at( |
| &mut self, |
| header_offset: u64, |
| uuid: &Uuid, |
| payload_size: u64, |
| ) -> Result<()> { |
| self.file.seek(SeekFrom::Start(header_offset))?; |
| self.file.write_all(uuid.as_bytes())?; |
| self.file.write_u64::<LittleEndian>(payload_size)?; |
| Ok(()) |
| } |
| |
| /// Locate the header of the partition for microdroid manager. A pair of `PartitionHeader` and |
| /// the offset of the partition in the disk is returned. If the partition is not found, |
| /// `PartitionHeader` is `None` and the offset points to the empty partition that can be used |
| /// for the partition. |
| fn locate_microdroid_header(&mut self) -> Result<(Option<PartitionHeader>, PartitionOffset)> { |
| let microdroid_uuid = Uuid::parse_str(MICRODROID_PARTITION_UUID)?; |
| |
| // the first partition header is located just after the disk header |
| let mut header_offset = DISK_HEADER_SIZE; |
| loop { |
| let header = self.read_header_at(header_offset)?; |
| if header.uuid == microdroid_uuid { |
| // found a matching header |
| return Ok((Some(header), header_offset)); |
| } else if header.uuid == Uuid::nil() { |
| // found an empty space |
| return Ok((None, header_offset)); |
| } |
| // Move to the next partition. Be careful about overflow. |
| let payload_size = round_to_multiple(header.payload_size, PARTITION_HEADER_SIZE)?; |
| let part_size = payload_size |
| .checked_add(PARTITION_HEADER_SIZE) |
| .ok_or_else(|| anyhow!("partition too large"))?; |
| header_offset = header_offset |
| .checked_add(part_size) |
| .ok_or_else(|| anyhow!("next partition at invalid offset"))?; |
| } |
| } |
| } |
| |
| /// Round `n` up to the nearest multiple of `unit` |
| fn round_to_multiple(n: u64, unit: u64) -> Result<u64> { |
| assert!((unit & (unit - 1)) == 0, "{} is not power of two", unit); |
| let ret = (n + unit - 1) & !(unit - 1); |
| if ret < n { |
| bail!("overflow") |
| } |
| Ok(ret) |
| } |
| |
| #[derive(Debug, Serialize, Deserialize, PartialEq, Eq)] |
| pub struct MicrodroidData { |
| // `salt` is obsolete, it was used as a differentiator for non-protected VM instances running |
| // same payload. Instance-id (present in DT) is used for that now. |
| pub salt: Vec<u8>, // Should be [u8; 64] but that isn't serializable. |
| pub apk_data: ApkData, |
| pub extra_apks_data: Vec<ApkData>, |
| pub apex_data: Vec<ApexData>, |
| } |
| |
| impl MicrodroidData { |
| pub fn extra_apk_root_hash_eq(&self, i: usize, root_hash: &[u8]) -> bool { |
| self.extra_apks_data.get(i).map_or(false, |apk| apk.root_hash_eq(root_hash)) |
| } |
| } |
| |
| #[derive(Debug, Serialize, Deserialize, PartialEq, Eq)] |
| pub struct ApkData { |
| pub root_hash: Vec<u8>, |
| pub cert_hash: Vec<u8>, |
| pub package_name: String, |
| pub version_code: u64, |
| } |
| |
| impl ApkData { |
| pub fn root_hash_eq(&self, root_hash: &[u8]) -> bool { |
| self.root_hash == root_hash |
| } |
| } |
| |
| #[derive(Debug, Serialize, Deserialize, PartialEq, Eq)] |
| pub struct ApexData { |
| pub name: String, |
| pub manifest_name: Option<String>, |
| pub manifest_version: Option<i64>, |
| pub public_key: Vec<u8>, |
| pub root_digest: Vec<u8>, |
| pub last_update_seconds: u64, |
| pub is_factory: bool, |
| } |