Kernel: Move Random.{h,cpp} code to Security subdirectory

Kernel/Security/Random.cpp

@@ -0,0 +1,176 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Peter Elliott <pelliott@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Singleton.h>
+#include <Kernel/Arch/Processor.h>
+#if ARCH(X86_64)
+#    include <Kernel/Arch/x86_64/Time/HPET.h>
+#    include <Kernel/Arch/x86_64/Time/RTC.h>
+#elif ARCH(AARCH64)
+#    include <Kernel/Arch/aarch64/ASM_wrapper.h>
+#endif
+#include <Kernel/Devices/Generic/RandomDevice.h>
+#include <Kernel/Sections.h>
+#include <Kernel/Security/Random.h>
+#include <Kernel/Time/TimeManagement.h>
+
+namespace Kernel {
+
+static Singleton<KernelRng> s_the;
+static Atomic<u32, AK::MemoryOrder::memory_order_relaxed> s_next_random_value = 1;
+
+KernelRng& KernelRng::the()
+{
+    return *s_the;
+}
+
+UNMAP_AFTER_INIT KernelRng::KernelRng()
+{
+#if ARCH(X86_64)
+    if (Processor::current().has_feature(CPUFeature::RDSEED)) {
+        dmesgln("KernelRng: Using RDSEED as entropy source");
+
+        for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
+            add_random_event(Kernel::read_rdseed(), i % 32);
+        }
+    } else if (Processor::current().has_feature(CPUFeature::RDRAND)) {
+        dmesgln("KernelRng: Using RDRAND as entropy source");
+
+        for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
+            add_random_event(Kernel::read_rdrand(), i % 32);
+        }
+    } else if (TimeManagement::the().can_query_precise_time()) {
+        // Add HPET as entropy source if we don't have anything better.
+        dmesgln("KernelRng: Using HPET as entropy source");
+
+        for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
+            u64 hpet_time = HPET::the().read_main_counter_unsafe();
+            add_random_event(hpet_time, i % 32);
+        }
+    } else {
+        // Fallback to RTC
+        dmesgln("KernelRng: Using RTC as entropy source (bad!)");
+        auto current_time = static_cast<u64>(RTC::now());
+        for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
+            add_random_event(current_time, i % 32);
+            current_time *= 0x574au;
+            current_time += 0x40b2u;
+        }
+    }
+#elif ARCH(AARCH64)
+    if (Processor::current().has_feature(CPUFeature::RNG)) {
+        dmesgln("KernelRng: Using RNDRRS as entropy source");
+        for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
+            add_random_event(Aarch64::Asm::read_rndrrs(), i % 32);
+        }
+    } else {
+        // Fallback to TimeManagement as entropy
+        dmesgln("KernelRng: Using bad entropy source TimeManagement");
+        auto current_time = static_cast<u64>(TimeManagement::now().milliseconds_since_epoch());
+        for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
+            add_random_event(current_time, i % 32);
+            current_time *= 0x574au;
+            current_time += 0x40b2u;
+        }
+    }
+#else
+    dmesgln("KernelRng: No entropy source available!");
+#endif
+}
+
+void KernelRng::wait_for_entropy()
+{
+    SpinlockLocker lock(get_lock());
+    if (!is_ready()) {
+        dbgln("Entropy starvation...");
+        m_seed_queue.wait_forever("KernelRng"sv);
+    }
+}
+
+void KernelRng::wake_if_ready()
+{
+    VERIFY(get_lock().is_locked());
+    if (is_ready()) {
+        m_seed_queue.wake_all();
+    }
+}
+
+size_t EntropySource::next_source { static_cast<size_t>(EntropySource::Static::MaxHardcodedSourceIndex) };
+
+static void do_get_fast_random_bytes(Bytes buffer)
+{
+
+    union {
+        u8 bytes[4];
+        u32 value;
+    } u;
+    size_t offset = 4;
+    for (size_t i = 0; i < buffer.size(); ++i) {
+        if (offset >= 4) {
+            auto current_next = s_next_random_value.load();
+            for (;;) {
+                auto new_next = current_next * 1103515245 + 12345;
+                if (s_next_random_value.compare_exchange_strong(current_next, new_next)) {
+                    u.value = new_next;
+                    break;
+                }
+            }
+            offset = 0;
+        }
+        buffer[i] = u.bytes[offset++];
+    }
+}
+
+bool get_good_random_bytes(Bytes buffer, bool allow_wait, bool fallback_to_fast)
+{
+    bool result = false;
+    auto& kernel_rng = KernelRng::the();
+    // FIXME: What if interrupts are disabled because we're in an interrupt?
+    bool can_wait = Processor::are_interrupts_enabled();
+    if (!can_wait && allow_wait) {
+        // If we can't wait but the caller would be ok with it, then we
+        // need to definitely fallback to *something*, even if it's less
+        // secure...
+        fallback_to_fast = true;
+    }
+    if (can_wait && allow_wait) {
+        for (;;) {
+            {
+                if (kernel_rng.get_random_bytes(buffer)) {
+                    result = true;
+                    break;
+                }
+            }
+            kernel_rng.wait_for_entropy();
+        }
+    } else {
+        // We can't wait/block here, or we are not allowed to block/wait
+        if (kernel_rng.get_random_bytes(buffer)) {
+            result = true;
+        } else if (fallback_to_fast) {
+            // If interrupts are disabled
+            do_get_fast_random_bytes(buffer);
+            result = true;
+        }
+    }
+
+    // NOTE: The only case where this function should ever return false and
+    // not actually return random data is if fallback_to_fast == false and
+    // allow_wait == false and interrupts are enabled!
+    VERIFY(result || !fallback_to_fast);
+    return result;
+}
+
+void get_fast_random_bytes(Bytes buffer)
+{
+    // Try to get good randomness, but don't block if we can't right now
+    // and allow falling back to fast randomness
+    auto result = get_good_random_bytes(buffer, false, true);
+    VERIFY(result);
+}
+
+}