compos/composd/src/instance_manager.rs

/*
 * Copyright (C) 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.
 */

//! Starts and manages instances of the CompOS VM. At most one instance should be running at
//! a time.

use android_system_virtualizationservice::aidl::android::system::virtualizationservice::{
    IVirtualizationService::IVirtualizationService, PartitionType::PartitionType,
};
use anyhow::{bail, Context, Result};
use compos_aidl_interface::aidl::com::android::compos::ICompOsService::ICompOsService;
use compos_aidl_interface::binder::{ParcelFileDescriptor, Strong};
use compos_common::compos_client::VmInstance;
use compos_common::{
    COMPOS_DATA_ROOT, CURRENT_DIR, INSTANCE_IMAGE_FILE, PRIVATE_KEY_BLOB_FILE, PUBLIC_KEY_FILE,
};
use log::{info, warn};
use std::fs;
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex, Weak};

pub struct CompOsInstance {
    #[allow(dead_code)] // Keeps VirtualizationService & the VM alive
    vm_instance: VmInstance,
    service: Strong<dyn ICompOsService>,
}

pub struct InstanceManager {
    service: Strong<dyn IVirtualizationService>,
    state: Mutex<State>,
}

impl InstanceManager {
    pub fn new(service: Strong<dyn IVirtualizationService>) -> Self {
        Self { service, state: Default::default() }
    }

    pub fn get_running_service(&self) -> Result<Strong<dyn ICompOsService>> {
        let mut state = self.state.lock().unwrap();
        let instance = state.get_running_instance().context("No running instance")?;
        Ok(instance.service.clone())
    }

    pub fn start_current_instance(&self) -> Result<Arc<CompOsInstance>> {
        let mut state = self.state.lock().unwrap();
        state.mark_starting()?;
        // Don't hold the lock while we start the instance to avoid blocking other callers.
        drop(state);

        let instance = self.try_start_current_instance();

        let mut state = self.state.lock().unwrap();
        if let Ok(ref instance) = instance {
            state.mark_started(instance)?;
        } else {
            state.mark_stopped();
        }
        instance
    }

    fn try_start_current_instance(&self) -> Result<Arc<CompOsInstance>> {
        let instance_files = InstanceFiles::new(CURRENT_DIR);

        let compos_instance = instance_files.create_or_start_instance(&*self.service)?;

        Ok(Arc::new(compos_instance))
    }
}

struct InstanceFiles {
    instance_name: String,
    instance_root: PathBuf,
    instance_image: PathBuf,
    key_blob: PathBuf,
    public_key: PathBuf,
}

impl InstanceFiles {
    fn new(instance_name: &str) -> Self {
        let instance_root = Path::new(COMPOS_DATA_ROOT).join(instance_name);
        let instant_root_path = instance_root.as_path();
        let instance_image = instant_root_path.join(INSTANCE_IMAGE_FILE);
        let key_blob = instant_root_path.join(PRIVATE_KEY_BLOB_FILE);
        let public_key = instant_root_path.join(PUBLIC_KEY_FILE);
        Self {
            instance_name: instance_name.to_owned(),
            instance_root,
            instance_image,
            key_blob,
            public_key,
        }
    }

    fn create_or_start_instance(
        &self,
        service: &dyn IVirtualizationService,
    ) -> Result<CompOsInstance> {
        let compos_instance = self.start_instance();
        match compos_instance {
            Ok(_) => return compos_instance,
            Err(e) => warn!("Failed to start {}: {}", self.instance_name, e),
        }

        self.start_new_instance(service)
    }

    fn start_instance(&self) -> Result<CompOsInstance> {
        // No point even trying if the files we need aren't there.
        self.check_files_exist()?;

        let key_blob = fs::read(&self.key_blob).context("Reading private key blob")?;
        let public_key = fs::read(&self.public_key).context("Reading public key")?;

        let vm_instance = VmInstance::start(&self.instance_image).context("Starting VM")?;
        let service = vm_instance.get_service().context("Connecting to CompOS")?;

        if !service.verifySigningKey(&key_blob, &public_key).context("Verifying key pair")? {
            bail!("Key pair invalid");
        }

        // If we get this far then the instance image is valid in the current context (e.g. the
        // current set of APEXes) and the key blob can be successfully decrypted by the VM. So the
        // files have not been tampered with and we're good to go.

        service.initializeSigningKey(&key_blob).context("Loading signing key")?;

        Ok(CompOsInstance { vm_instance, service })
    }

    fn start_new_instance(
        &self,
        virtualization_service: &dyn IVirtualizationService,
    ) -> Result<CompOsInstance> {
        info!("Creating {} CompOs instance", self.instance_name);

        // Ignore failure here - the directory may already exist.
        let _ = fs::create_dir(&self.instance_root);

        self.create_instance_image(virtualization_service)?;

        let vm_instance = VmInstance::start(&self.instance_image).context("Starting VM")?;
        let service = vm_instance.get_service().context("Connecting to CompOS")?;

        let key_data = service.generateSigningKey().context("Generating signing key")?;
        fs::write(&self.key_blob, &key_data.keyBlob).context("Writing key blob")?;
        // TODO: Extract public key from cert
        fs::write(&self.public_key, &key_data.certificate).context("Writing public key")?;

        // We don't need to verify the key, since we just generated it and have it in memory.

        service.initializeSigningKey(&key_data.keyBlob).context("Loading signing key")?;

        Ok(CompOsInstance { vm_instance, service })
    }

    fn create_instance_image(
        &self,
        virtualization_service: &dyn IVirtualizationService,
    ) -> Result<()> {
        let instance_image = fs::OpenOptions::new()
            .create(true)
            .read(true)
            .write(true)
            .open(&self.instance_image)
            .context("Creating instance image file")?;
        let instance_image = ParcelFileDescriptor::new(instance_image);
        // TODO: Where does this number come from?
        let size = 10 * 1024 * 1024;
        virtualization_service
            .initializeWritablePartition(&instance_image, size, PartitionType::ANDROID_VM_INSTANCE)
            .context("Writing instance image file")?;
        Ok(())
    }

    fn check_files_exist(&self) -> Result<()> {
        if !self.instance_root.is_dir() {
            bail!("Directory {} not found", self.instance_root.display())
        };
        Self::check_file_exists(&self.instance_image)?;
        Self::check_file_exists(&self.key_blob)?;
        Self::check_file_exists(&self.public_key)?;
        Ok(())
    }

    fn check_file_exists(file: &Path) -> Result<()> {
        if !file.is_file() {
            bail!("File {} not found", file.display())
        };
        Ok(())
    }
}

// Ensures we only run one instance at a time.
// Valid states:
// Starting: is_starting is true, running_instance is None.
// Started: is_starting is false, running_instance is Some(x) and there is a strong ref to x.
// Stopped: is_starting is false and running_instance is None or a weak ref to a dropped instance.
// The panic calls here should never happen, unless the code above in InstanceManager is buggy.
// In particular nothing the client does should be able to trigger them.
#[derive(Default)]
struct State {
    running_instance: Option<Weak<CompOsInstance>>,
    is_starting: bool,
}

impl State {
    // Move to Starting iff we are Stopped.
    fn mark_starting(&mut self) -> Result<()> {
        if self.is_starting {
            bail!("An instance is already starting");
        }
        if let Some(weak) = &self.running_instance {
            if weak.strong_count() != 0 {
                bail!("An instance is already running");
            }
        }
        self.running_instance = None;
        self.is_starting = true;
        Ok(())
    }

    // Move from Starting to Stopped.
    fn mark_stopped(&mut self) {
        if !self.is_starting || self.running_instance.is_some() {
            panic!("Tried to mark stopped when not starting");
        }
        self.is_starting = false;
    }

    // Move from Starting to Started.
    fn mark_started(&mut self, instance: &Arc<CompOsInstance>) -> Result<()> {
        if !self.is_starting {
            panic!("Tried to mark started when not starting")
        }
        if self.running_instance.is_some() {
            panic!("Attempted to mark started when already started");
        }
        self.is_starting = false;
        self.running_instance = Some(Arc::downgrade(instance));
        Ok(())
    }

    // Return the running instance if we are in the Started state.
    fn get_running_instance(&mut self) -> Option<Arc<CompOsInstance>> {
        if self.is_starting {
            return None;
        }
        let instance = self.running_instance.as_ref()?.upgrade();
        if instance.is_none() {
            // No point keeping an orphaned weak reference
            self.running_instance = None;
        }
        instance
    }
}