zircon/kernel/lib/crypto/include/lib/crypto/entropy/hw_rng_collector.h

// Copyright 2017 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#ifndef ZIRCON_KERNEL_LIB_CRYPTO_INCLUDE_LIB_CRYPTO_ENTROPY_HW_RNG_COLLECTOR_H_
#define ZIRCON_KERNEL_LIB_CRYPTO_INCLUDE_LIB_CRYPTO_ENTROPY_HW_RNG_COLLECTOR_H_

#include <lib/crypto/entropy/collector.h>
#include <zircon/types.h>

#include <kernel/mutex.h>

namespace crypto {

namespace entropy {

// An implementation of crypto::entropy::Collector that uses hw_rng_draw_entropy
// as its entropy source. Currently, this is only supported on x86.
class HwRngCollector : public Collector {
 public:
  // Gets the current HwRngCollector instance. Returns ZX_ERR_NOT_SUPPORTED if
  // hw_rng_draw_entropy is not supported.
  //
  // This function is thread-safe, and the DrawEntropy() method of the global
  // HwRngCollector instance is also thread-safe.
  static zx_status_t GetInstance(Collector** ptr);

  // Inherited from crypto::entropy::Collector; see comments there.
  //
  // Note that this method internally uses a mutex to prevent multiple
  // accesses. It is safe to call this method from multiple threads, but it
  // may block.
  //
  // TODO(andrewkrieger): Determine what level of thread safety is needed for
  // RNG reseeding, and support it more uniformly (e.g. have a thread safety
  // contract for Collector::DrawEntropy, obeyed by all implementations).
  size_t DrawEntropy(uint8_t* buf, size_t len) override;

  HwRngCollector();

 private:
  DISALLOW_COPY_ASSIGN_AND_MOVE(HwRngCollector);

  DECLARE_MUTEX(HwRngCollector) lock_;
};

}  // namespace entropy

}  // namespace crypto

#endif  // ZIRCON_KERNEL_LIB_CRYPTO_INCLUDE_LIB_CRYPTO_ENTROPY_HW_RNG_COLLECTOR_H_