1 files changed, 203 insertions, 0 deletions
diff --git a/Kernel/Security/Random.h b/Kernel/Security/Random.h
new file mode 100644
index 0000000000..2ae6bd91f1
--- /dev/null
+++ b/Kernel/Security/Random.h
@@ -0,0 +1,203 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Peter Elliott <pelliott@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Assertions.h>
+#include <AK/ByteBuffer.h>
+#include <AK/Types.h>
+#include <Kernel/Arch/Processor.h>
+#include <Kernel/Locking/Mutex.h>
+#include <Kernel/StdLib.h>
+#include <LibCrypto/Cipher/AES.h>
+#include <LibCrypto/Cipher/Cipher.h>
+#include <LibCrypto/Hash/SHA2.h>
+
+namespace Kernel {
+
+template<typename CipherT, typename HashT, int KeySize>
+class FortunaPRNG {
+public:
+    constexpr static size_t pool_count = 32;
+    constexpr static size_t reseed_threshold = 16;
+
+    using CipherType = CipherT;
+    using BlockType = typename CipherT::BlockType;
+    using HashType = HashT;
+    using DigestType = typename HashT::DigestType;
+
+    // FIXME: Do something other than VERIFY()'ing in case of OOM.
+    FortunaPRNG()
+        : m_counter(ByteBuffer::create_zeroed(BlockType::block_size()).release_value_but_fixme_should_propagate_errors())
+    {
+    }
+
+    bool get_random_bytes(Bytes buffer)
+    {
+        SpinlockLocker lock(m_lock);
+        if (!is_ready())
+            return false;
+        if (m_p0_len >= reseed_threshold) {
+            this->reseed();
+        }
+
+        VERIFY(is_seeded());
+
+        // FIXME: More than 2^20 bytes cannot be generated without refreshing the key.
+        VERIFY(buffer.size() < (1 << 20));
+
+        typename CipherType::CTRMode cipher(m_key, KeySize, Crypto::Cipher::Intent::Encryption);
+
+        auto counter_span = m_counter.bytes();
+        cipher.key_stream(buffer, counter_span, &counter_span);
+
+        // Extract a new key from the prng stream.
+        Bytes key_span = m_key.bytes();
+        cipher.key_stream(key_span, counter_span, &counter_span);
+        return true;
+    }
+
+    template<typename T>
+    void add_random_event(T const& event_data, size_t pool)
+    {
+        pool %= pool_count;
+        if (pool == 0) {
+            m_p0_len++;
+        }
+        m_pools[pool].update(reinterpret_cast<u8 const*>(&event_data), sizeof(T));
+    }
+
+    [[nodiscard]] bool is_seeded() const
+    {
+        return m_reseed_number > 0;
+    }
+
+    [[nodiscard]] bool is_ready() const
+    {
+        VERIFY(m_lock.is_locked());
+        return is_seeded() || m_p0_len >= reseed_threshold;
+    }
+
+    Spinlock<LockRank::None>& get_lock() { return m_lock; }
+
+private:
+    void reseed()
+    {
+        HashType new_key;
+        new_key.update(m_key);
+        for (size_t i = 0; i < pool_count; ++i) {
+            if (m_reseed_number % (1u << i) == 0) {
+                DigestType digest = m_pools[i].digest();
+                new_key.update(digest.immutable_data(), digest.data_length());
+            }
+        }
+        DigestType digest = new_key.digest();
+        if (m_key.size() == digest.data_length()) {
+            // Avoid reallocating, just overwrite the key.
+            m_key.overwrite(0, digest.immutable_data(), digest.data_length());
+        } else {
+            auto buffer_result = ByteBuffer::copy(digest.immutable_data(), digest.data_length());
+            // If there's no memory left to copy this into, bail out.
+            if (buffer_result.is_error())
+                return;
+
+            m_key = buffer_result.release_value();
+        }
+
+        m_reseed_number++;
+        m_p0_len = 0;
+    }
+
+    ByteBuffer m_counter;
+    size_t m_reseed_number { 0 };
+    size_t m_p0_len { 0 };
+    ByteBuffer m_key;
+    HashType m_pools[pool_count];
+    Spinlock<LockRank::None> m_lock {};
+};
+
+class KernelRng : public FortunaPRNG<Crypto::Cipher::AESCipher, Crypto::Hash::SHA256, 256> {
+
+public:
+    KernelRng();
+    static KernelRng& the();
+
+    void wait_for_entropy();
+
+    void wake_if_ready();
+
+private:
+    WaitQueue m_seed_queue;
+};
+
+class EntropySource {
+    template<typename T>
+    struct Event {
+        u64 timestamp;
+        size_t source;
+        T event_data;
+    };
+
+public:
+    enum class Static : size_t {
+        Interrupts,
+        MaxHardcodedSourceIndex,
+    };
+
+    EntropySource()
+        : m_source(next_source++)
+    {
+    }
+
+    EntropySource(Static hardcoded_source)
+        : m_source(static_cast<size_t>(hardcoded_source))
+    {
+    }
+
+    template<typename T>
+    void add_random_event(T const& event_data)
+    {
+        auto& kernel_rng = KernelRng::the();
+        SpinlockLocker lock(kernel_rng.get_lock());
+        // We don't lock this because on the off chance a pool is corrupted, entropy isn't lost.
+        Event<T> event = { Processor::read_cpu_counter(), m_source, event_data };
+        kernel_rng.add_random_event(event, m_pool);
+        m_pool++;
+        kernel_rng.wake_if_ready();
+    }
+
+private:
+    static size_t next_source;
+    size_t m_pool { 0 };
+    size_t m_source;
+};
+
+// NOTE: These API's are primarily about expressing intent/needs in the calling code.
+//       The only difference is that get_fast_random is guaranteed not to block.
+
+void get_fast_random_bytes(Bytes);
+bool get_good_random_bytes(Bytes bytes, bool allow_wait = true, bool fallback_to_fast = true);
+
+template<typename T>
+inline T get_fast_random()
+{
+    T value;
+    Bytes bytes { reinterpret_cast<u8*>(&value), sizeof(T) };
+    get_fast_random_bytes(bytes);
+    return value;
+}
+
+template<typename T>
+inline T get_good_random()
+{
+    T value;
+    Bytes bytes { reinterpret_cast<u8*>(&value), sizeof(T) };
+    get_good_random_bytes(bytes);
+    return value;
+}
+
+}