mirror of
https://github.com/SerenityOS/serenity
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183 lines
6.3 KiB
C++
183 lines
6.3 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@ualberta.ca>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <AK/Singleton.h>
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#include <Kernel/Arch/i386/CPU.h>
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#include <Kernel/Devices/RandomDevice.h>
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#include <Kernel/Random.h>
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#include <Kernel/Time/HPET.h>
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#include <Kernel/Time/RTC.h>
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#include <Kernel/Time/TimeManagement.h>
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namespace Kernel {
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static AK::Singleton<KernelRng> s_the;
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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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bool supports_rdseed = Processor::current().has_feature(CPUFeature::RDSEED);
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bool supports_rdrand = Processor::current().has_feature(CPUFeature::RDRAND);
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if (supports_rdseed || supports_rdrand) {
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klog() << "KernelRng: Using RDSEED or RDRAND as entropy source";
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for (size_t i = 0; i < resource().pool_count * resource().reseed_threshold; ++i) {
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u32 value = 0;
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if (supports_rdseed) {
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asm volatile(
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"1:\n"
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"rdseed %0\n"
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"jnc 1b\n"
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: "=r"(value));
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} else {
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asm volatile(
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"1:\n"
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"rdrand %0\n"
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"jnc 1b\n"
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: "=r"(value));
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}
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this->resource().add_random_event(value, 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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klog() << "KernelRng: Using HPET as entropy source";
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for (size_t i = 0; i < resource().pool_count * resource().reseed_threshold; ++i) {
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u64 hpet_time = HPET::the().read_main_counter();
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this->resource().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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klog() << "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 < resource().pool_count * resource().reseed_threshold; ++i) {
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this->resource().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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}
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void KernelRng::wait_for_entropy()
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{
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ScopedSpinLock lock(get_lock());
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if (!resource().is_ready()) {
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dbgln("Entropy starvation...");
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m_seed_queue.wait_forever("KernelRng");
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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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ASSERT(get_lock().is_locked());
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if (resource().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(u8* buffer, size_t buffer_size)
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{
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static Atomic<u32, AK::MemoryOrder::memory_order_relaxed> next = 1;
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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 = next.load();
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for (;;) {
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auto new_next = current_next * 1103515245 + 12345;
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if (next.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(u8* buffer, size_t buffer_size, 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 = 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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LOCKER(KernelRng::the().lock());
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if (kernel_rng.resource().get_random_bytes(buffer, buffer_size)) {
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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.resource().get_random_bytes(buffer, buffer_size)) {
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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, buffer_size);
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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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ASSERT(result || !fallback_to_fast);
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return result;
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}
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void get_fast_random_bytes(u8* buffer, size_t buffer_size)
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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, buffer_size, false, true);
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ASSERT(result);
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}
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}
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