Microdroid: Map a dm-crypt dev on (virtio-blk)disk
1. microdroid_manager, on seeing a (named) block device dedicated for
storage, will run encryptedstore binary.
2. The key derived for the encryption will be derived from the dice
using the CDIs of *payload* as hashes.
3. encryptedstore binary will create the dm-crypt device using the
libdm_rust library.
Note: The salt used for the key is deterministic but I randomly got from
/dev/urandom. This ensures the key & payload secret are different.
Test: Run bin/vm run-app using --storage & --storage-size flag
Test: Write into the crypt device & check persistence by running another
VM with same instance image.
Bug: 241541860
Change-Id: I11d00343a040935dd90a232fe7c5ab4e06b6d145
diff --git a/encryptedstore/Android.bp b/encryptedstore/Android.bp
new file mode 100644
index 0000000..301e733
--- /dev/null
+++ b/encryptedstore/Android.bp
@@ -0,0 +1,30 @@
+package {
+ default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+rust_defaults {
+ name: "encryptedstore.defaults",
+ srcs: ["src/main.rs"],
+ edition: "2021",
+ prefer_rlib: true,
+ rustlibs: [
+ "libandroid_logger",
+ "libanyhow",
+ "libclap",
+ "libhex",
+ "liblog_rust",
+ "libnix",
+ "libdm_rust",
+ ],
+ multilib: {
+ lib32: {
+ enabled: false,
+ },
+ },
+}
+
+rust_binary {
+ name: "encryptedstore",
+ defaults: ["encryptedstore.defaults"],
+ bootstrap: true,
+}
diff --git a/encryptedstore/src/main.rs b/encryptedstore/src/main.rs
new file mode 100644
index 0000000..9a701ed
--- /dev/null
+++ b/encryptedstore/src/main.rs
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2022 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.
+ */
+
+//! `encryptedstore` is a program that (as the name indicates) provides encrypted storage
+//! solution in a VM. This is based on dm-crypt & requires the (64 bytes') key & the backing device.
+//! It uses dm_rust lib.
+
+use anyhow::{ensure, Context, Result};
+use clap::{arg, App};
+use dm::{crypt::CipherType, util};
+use log::info;
+use std::os::unix::fs::FileTypeExt;
+use std::path::Path;
+
+fn main() -> Result<()> {
+ android_logger::init_once(
+ android_logger::Config::default()
+ .with_tag("encryptedstore")
+ .with_min_level(log::Level::Info),
+ );
+ info!("Starting encryptedstore binary");
+
+ let matches = App::new("encryptedstore")
+ .args(&[
+ arg!(--blkdevice <FILE> "the block device backing the encrypted storage")
+ .required(true),
+ arg!(--key <KEY> "key (in hex) equivalent to 64 bytes)").required(true),
+ ])
+ .get_matches();
+
+ let blkdevice = Path::new(matches.value_of("blkdevice").unwrap());
+ let key = matches.value_of("key").unwrap();
+ ensure!(
+ std::fs::metadata(&blkdevice)
+ .context(format!("Failed to get metadata of {:?}", blkdevice))?
+ .file_type()
+ .is_block_device(),
+ "The path:{:?} is not of a block device",
+ blkdevice
+ );
+
+ enable_crypt(blkdevice, key, "cryptdev")?;
+ Ok(())
+}
+
+fn enable_crypt(data_device: &Path, key: &str, name: &str) -> Result<()> {
+ let dev_size = util::blkgetsize64(data_device)?;
+ let key = hex::decode(key).context("Unable to decode hex key")?;
+ ensure!(key.len() == 64, "We need 64 bytes' key for aes-xts cipher for block encryption");
+
+ // Create the dm-crypt spec
+ let target = dm::crypt::DmCryptTargetBuilder::default()
+ .data_device(data_device, dev_size)
+ .cipher(CipherType::AES256XTS) // TODO(b/259253336) Move to HCTR2 based encryption.
+ .key(&key)
+ .build()
+ .context("Couldn't build the DMCrypt target")?;
+ let dm = dm::DeviceMapper::new()?;
+ dm.create_crypt_device(name, &target).context("Failed to create dm-crypt device")?;
+
+ Ok(())
+}
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index c3e2692..68827df 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -108,6 +108,7 @@
"apkdmverity",
"authfs",
"authfs_service",
+ "encryptedstore",
"microdroid_crashdump_kernel",
"microdroid_kexec",
"microdroid_manager",
diff --git a/microdroid_manager/Android.bp b/microdroid_manager/Android.bp
index 4b06b3e..44b4c01 100644
--- a/microdroid_manager/Android.bp
+++ b/microdroid_manager/Android.bp
@@ -23,6 +23,7 @@
"libdiced_sample_inputs",
"libdiced_utils",
"libglob",
+ "libhex",
"libitertools",
"libkernlog",
"libkeystore2_crypto_rust",
diff --git a/microdroid_manager/src/dice.rs b/microdroid_manager/src/dice.rs
index 3881db3..499835f 100644
--- a/microdroid_manager/src/dice.rs
+++ b/microdroid_manager/src/dice.rs
@@ -38,6 +38,16 @@
pub bcc: Vec<u8>,
}
+impl DiceContext {
+ pub fn get_sealing_key(&self, salt: &[u8], identifier: &[u8], keysize: u32) -> Result<ZVec> {
+ // Deterministically derive a key to use for sealing data based on salt. Use different salt
+ // for different keys.
+ let mut key = ZVec::new(keysize as usize)?;
+ hkdf(&mut key, Md::sha256(), &self.cdi_seal, salt, identifier)?;
+ Ok(key)
+ }
+}
+
/// Artifacts that are mapped into the process address space from the driver.
pub enum DiceDriver<'a> {
Real {
diff --git a/microdroid_manager/src/main.rs b/microdroid_manager/src/main.rs
index c18dd26..cc4b9dc 100644
--- a/microdroid_manager/src/main.rs
+++ b/microdroid_manager/src/main.rs
@@ -80,6 +80,12 @@
// SYNC WITH virtualizationservice/src/crosvm.rs
const FAILURE_SERIAL_DEVICE: &str = "/dev/ttyS1";
+/// Identifier for the key used for encrypted store.
+const ENCRYPTEDSTORE_BACKING_DEVICE: &str = "/dev/block/by-name/encryptedstore";
+const ENCRYPTEDSTORE_BIN: &str = "/system/bin/encryptedstore";
+const ENCRYPTEDSTORE_KEY_IDENTIFIER: &str = "encryptedstore_key";
+const ENCRYPTEDSTORE_KEYSIZE: u32 = 64;
+
#[derive(thiserror::Error, Debug)]
enum MicrodroidError {
#[error("Cannot connect to virtualization service: {0}")]
@@ -350,7 +356,15 @@
// To minimize the exposure to untrusted data, derive dice profile as soon as possible.
info!("DICE derivation for payload");
- let dice = dice_derivation(dice, &verified_data, &payload_metadata)?;
+ let dice_context = dice_derivation(dice, &verified_data, &payload_metadata)?;
+
+ // Run encryptedstore binary to prepare the storage
+ let encryptedstore_child = if Path::new(ENCRYPTEDSTORE_BACKING_DEVICE).exists() {
+ info!("Preparing encryptedstore ...");
+ Some(prepare_encryptedstore(&dice_context).context("encryptedstore run")?)
+ } else {
+ None
+ };
// Before reading a file from the APK, start zipfuse
run_zipfuse(
@@ -404,7 +418,12 @@
// Wait until zipfuse has mounted the APK so we can access the payload
wait_for_property_true(APK_MOUNT_DONE_PROP).context("Failed waiting for APK mount done")?;
- register_vm_payload_service(allow_restricted_apis, service.clone(), dice)?;
+ register_vm_payload_service(allow_restricted_apis, service.clone(), dice_context)?;
+
+ if let Some(mut child) = encryptedstore_child {
+ let exitcode = child.wait().context("Wait for encryptedstore child")?;
+ ensure!(exitcode.success(), "Unable to prepare encrypted storage. Exitcode={}", exitcode);
+ }
system_properties::write("dev.bootcomplete", "1").context("set dev.bootcomplete")?;
exec_task(task, service).context("Failed to run payload")
@@ -802,3 +821,27 @@
fn to_hex_string(buf: &[u8]) -> String {
buf.iter().map(|b| format!("{:02X}", b)).collect()
}
+
+fn prepare_encryptedstore(dice: &DiceContext) -> Result<Child> {
+ // Use a fixed salt to scope the derivation to this API.
+ // Generated using hexdump -vn32 -e'14/1 "0x%02X, " 1 "\n"' /dev/urandom
+ // TODO(b/241541860) : Move this (& other salts) to a salt container, i.e. a global enum
+ let salt = [
+ 0xFC, 0x1D, 0x35, 0x7B, 0x96, 0xF3, 0xEF, 0x17, 0x78, 0x7D, 0x70, 0xED, 0xEA, 0xFE, 0x1D,
+ 0x6F, 0xB3, 0xF9, 0x40, 0xCE, 0xDD, 0x99, 0x40, 0xAA, 0xA7, 0x0E, 0x92, 0x73, 0x90, 0x86,
+ 0x4A, 0x75,
+ ];
+ let key = dice.get_sealing_key(
+ &salt,
+ ENCRYPTEDSTORE_KEY_IDENTIFIER.as_bytes(),
+ ENCRYPTEDSTORE_KEYSIZE,
+ )?;
+
+ let mut cmd = Command::new(ENCRYPTEDSTORE_BIN);
+ cmd.arg("--blkdevice")
+ .arg(ENCRYPTEDSTORE_BACKING_DEVICE)
+ .arg("--key")
+ .arg(hex::encode(&*key))
+ .spawn()
+ .context("encryptedstore failed")
+}
diff --git a/virtualizationservice/src/payload.rs b/virtualizationservice/src/payload.rs
index 233e74b..f6e8a7b 100644
--- a/virtualizationservice/src/payload.rs
+++ b/virtualizationservice/src/payload.rs
@@ -420,7 +420,7 @@
if let Some(file) = storage_image {
writable_partitions.push(Partition {
- label: "encrypted-storage".to_owned(),
+ label: "encryptedstore".to_owned(),
image: Some(ParcelFileDescriptor::new(file)),
writable: true,
});