system/dev/bus/virtio/rng.h

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#pragma once

#include "device.h"
#include "ring.h"
#include <ddk/io-buffer.h>
#include <stdlib.h>
#include <zircon/compiler.h>

namespace virtio {

class Ring;

class RngDevice : public Device {
public:
    RngDevice(zx_device_t* bus_device, zx::bti bti, fbl::unique_ptr<Backend> backend);
    virtual ~RngDevice();

    zx_status_t Init() override;

    void IrqRingUpdate() override;
    void IrqConfigChange() override;
    const char* tag() const override { return "virtio-rng"; }

protected:
private:
    // TODO(SEC-29): The kernel should trigger entropy requests, instead of relying on this
    // userspace thread to push entropy whenever it wants to. As a temporary hack, this thread
    // pushes entropy to the kernel every 300 seconds instead.

    // the entry point for the entropy seeding thread
    static int SeedThreadEntry(void* arg);

    // the method called by SeedThreadEntry() to actually launch a request
    zx_status_t Request();

    // the thread that seeds the system CPRNG periodically
    thrd_t seed_thread_;

    // the virtio ring
    static constexpr uint16_t kRingIndex = 0;
    static constexpr uint16_t kRingSize = 1;
    Ring vring_ = {this};

    // the buffer used to receive entropy
    static constexpr size_t kBufferSize = ZX_CPRNG_ADD_ENTROPY_MAX_LEN;
    io_buffer_t buf_;
};

} // namespace virtio