cloud-hypervisor/virtio-devices/src/rng.rs

// Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause

use std::fs::File;
use std::os::unix::io::AsRawFd;
use std::sync::atomic::AtomicBool;
use std::sync::{Arc, Barrier};
use std::{io, result};

use anyhow::anyhow;
use event_monitor::event;
use log::{error, info};
use seccompiler::SeccompAction;
use serde::{Deserialize, Serialize};
use thiserror::Error;
use virtio_queue::{Queue, QueueT};
use vm_memory::{GuestAddressSpace, GuestMemory, GuestMemoryAtomic};
use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
use vm_virtio::{AccessPlatform, Translatable};
use vmm_sys_util::eventfd::EventFd;

use super::{
    ActivateError, ActivateResult, EPOLL_HELPER_EVENT_LAST, EpollHelper, EpollHelperError,
    EpollHelperHandler, Error as DeviceError, VIRTIO_F_ACCESS_PLATFORM, VIRTIO_F_VERSION_1,
    VirtioCommon, VirtioDevice, VirtioDeviceType,
};
use crate::seccomp_filters::Thread;
use crate::thread_helper::spawn_virtio_thread;
use crate::{GuestMemoryMmap, VirtioInterrupt, VirtioInterruptType};

const QUEUE_SIZE: u16 = 256;
const QUEUE_SIZES: &[u16] = &[QUEUE_SIZE];

// New descriptors are pending on the virtio queue.
const QUEUE_AVAIL_EVENT: u16 = EPOLL_HELPER_EVENT_LAST + 1;

#[derive(Error, Debug)]
enum Error {
    #[error("Descriptor chain too short")]
    DescriptorChainTooShort,
    #[error("Invalid descriptor")]
    InvalidDescriptor,
    #[error("Failed to write to guest memory")]
    GuestMemoryWrite(#[source] vm_memory::guest_memory::Error),
    #[error("Failed adding used index")]
    QueueAddUsed(#[source] virtio_queue::Error),
}

struct RngEpollHandler {
    mem: GuestMemoryAtomic<GuestMemoryMmap>,
    queue: Queue,
    random_file: File,
    interrupt_cb: Arc<dyn VirtioInterrupt>,
    queue_evt: EventFd,
    kill_evt: EventFd,
    pause_evt: EventFd,
    access_platform: Option<Arc<dyn AccessPlatform>>,
}

impl RngEpollHandler {
    fn process_queue(&mut self) -> result::Result<bool, Error> {
        let queue = &mut self.queue;

        let mut used_descs = false;
        while let Some(mut desc_chain) = queue.pop_descriptor_chain(self.mem.memory()) {
            let desc = desc_chain.next().ok_or(Error::DescriptorChainTooShort)?;

            // The descriptor must be write-only and non-zero length
            if !(desc.is_write_only() && desc.len() > 0) {
                return Err(Error::InvalidDescriptor);
            }

            // Fill the read with data from the random device on the host.
            let len = desc_chain
                .memory()
                .read_volatile_from(
                    desc.addr()
                        .translate_gva(self.access_platform.as_deref(), desc.len() as usize),
                    &mut self.random_file,
                    desc.len() as usize,
                )
                .map_err(Error::GuestMemoryWrite)?;

            queue
                .add_used(desc_chain.memory(), desc_chain.head_index(), len as u32)
                .map_err(Error::QueueAddUsed)?;
            used_descs = true;
        }

        Ok(used_descs)
    }

    fn signal_used_queue(&self) -> result::Result<(), DeviceError> {
        self.interrupt_cb
            .trigger(VirtioInterruptType::Queue(0))
            .map_err(|e| {
                error!("Failed to signal used queue: {e:?}");
                DeviceError::FailedSignalingUsedQueue(e)
            })
    }

    fn run(
        &mut self,
        paused: &AtomicBool,
        paused_sync: &Barrier,
    ) -> result::Result<(), EpollHelperError> {
        let mut helper = EpollHelper::new(&self.kill_evt, &self.pause_evt)?;
        helper.add_event(self.queue_evt.as_raw_fd(), QUEUE_AVAIL_EVENT)?;
        helper.run(paused, paused_sync, self)?;

        Ok(())
    }
}

impl EpollHelperHandler for RngEpollHandler {
    fn handle_event(
        &mut self,
        _helper: &mut EpollHelper,
        event: &epoll::Event,
    ) -> result::Result<(), EpollHelperError> {
        let ev_type = event.data as u16;
        match ev_type {
            QUEUE_AVAIL_EVENT => {
                self.queue_evt.read().map_err(|e| {
                    EpollHelperError::HandleEvent(anyhow!("Failed to get queue event: {e:?}"))
                })?;
                let needs_notification = self.process_queue().map_err(|e| {
                    EpollHelperError::HandleEvent(anyhow!("Failed to process queue : {e:?}"))
                })?;
                if needs_notification {
                    self.signal_used_queue().map_err(|e| {
                        EpollHelperError::HandleEvent(anyhow!("Failed to signal used queue: {e:?}"))
                    })?;
                }
            }
            _ => {
                return Err(EpollHelperError::HandleEvent(anyhow!(
                    "Unexpected event: {ev_type}"
                )));
            }
        }
        Ok(())
    }
}

/// Virtio device for exposing entropy to the guest OS through virtio.
pub struct Rng {
    common: VirtioCommon,
    id: String,
    random_file: Option<File>,
    seccomp_action: SeccompAction,
    exit_evt: EventFd,
}

#[derive(Deserialize, Serialize)]
pub struct RngState {
    pub avail_features: u64,
    pub acked_features: u64,
}

impl Rng {
    /// Create a new virtio rng device that gets random data from /dev/urandom.
    pub fn new(
        id: String,
        path: &str,
        iommu: bool,
        seccomp_action: SeccompAction,
        exit_evt: EventFd,
        state: Option<RngState>,
    ) -> io::Result<Rng> {
        let random_file = File::open(path)?;

        let (avail_features, acked_features, paused) = if let Some(state) = state {
            info!("Restoring virtio-rng {id}");
            (state.avail_features, state.acked_features, true)
        } else {
            let mut avail_features = 1u64 << VIRTIO_F_VERSION_1;

            if iommu {
                avail_features |= 1u64 << VIRTIO_F_ACCESS_PLATFORM;
            }

            (avail_features, 0, false)
        };

        Ok(Rng {
            common: VirtioCommon {
                device_type: VirtioDeviceType::Rng as u32,
                queue_sizes: QUEUE_SIZES.to_vec(),
                paused_sync: Some(Arc::new(Barrier::new(2))),
                avail_features,
                acked_features,
                min_queues: 1,
                paused: Arc::new(AtomicBool::new(paused)),
                ..Default::default()
            },
            id,
            random_file: Some(random_file),
            seccomp_action,
            exit_evt,
        })
    }

    fn state(&self) -> RngState {
        RngState {
            avail_features: self.common.avail_features,
            acked_features: self.common.acked_features,
        }
    }

    #[cfg(fuzzing)]
    pub fn wait_for_epoll_threads(&mut self) {
        self.common.wait_for_epoll_threads();
    }
}

impl Drop for Rng {
    fn drop(&mut self) {
        if let Some(kill_evt) = self.common.kill_evt.take() {
            // Ignore the result because there is nothing we can do about it.
            let _ = kill_evt.write(1);
        }
        self.common.wait_for_epoll_threads();
    }
}

impl VirtioDevice for Rng {
    fn device_type(&self) -> u32 {
        self.common.device_type
    }

    fn queue_max_sizes(&self) -> &[u16] {
        &self.common.queue_sizes
    }

    fn features(&self) -> u64 {
        self.common.avail_features
    }

    fn ack_features(&mut self, value: u64) {
        self.common.ack_features(value);
    }

    fn activate(&mut self, context: crate::device::ActivationContext) -> ActivateResult {
        let crate::device::ActivationContext {
            mem,
            interrupt_cb,
            mut queues,
            ..
        } = context;
        self.common.activate(&queues, interrupt_cb.clone())?;
        let (kill_evt, pause_evt) = self.common.dup_eventfds();

        if let Some(file) = self.random_file.as_ref() {
            let random_file = file.try_clone().map_err(|e| {
                error!("failed cloning rng source: {e}");
                ActivateError::BadActivate
            })?;

            let (_, queue, queue_evt) = queues.remove(0);

            let mut handler = RngEpollHandler {
                mem,
                queue,
                random_file,
                interrupt_cb,
                queue_evt,
                kill_evt,
                pause_evt,
                access_platform: self.common.access_platform.clone(),
            };

            let paused = self.common.paused.clone();
            let paused_sync = self.common.paused_sync.clone();
            let mut epoll_threads = Vec::new();
            spawn_virtio_thread(
                &self.id,
                &self.seccomp_action,
                Thread::VirtioRng,
                &mut epoll_threads,
                &self.exit_evt,
                move || handler.run(&paused, paused_sync.as_ref().unwrap()),
            )?;

            self.common.epoll_threads = Some(epoll_threads);

            event!("virtio-device", "activated", "id", &self.id);
            return Ok(());
        }
        Err(ActivateError::BadActivate)
    }

    fn reset(&mut self) -> Option<Arc<dyn VirtioInterrupt>> {
        let result = self.common.reset();
        event!("virtio-device", "reset", "id", &self.id);
        result
    }

    fn set_access_platform(&mut self, access_platform: Arc<dyn AccessPlatform>) {
        self.common.set_access_platform(access_platform);
    }
}

impl Pausable for Rng {
    fn pause(&mut self) -> result::Result<(), MigratableError> {
        self.common.pause()
    }

    fn resume(&mut self) -> result::Result<(), MigratableError> {
        self.common.resume()
    }
}

impl Snapshottable for Rng {
    fn id(&self) -> String {
        self.id.clone()
    }

    fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
        Snapshot::new_from_state(&self.state())
    }
}

impl Transportable for Rng {}
impl Migratable for Rng {}