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