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AK: Add windows support in AK/Random

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This commit adds support in AK/Random for a high quality RNG on windows.
This requires moving the code into a cpp file not to spread windows
headers around.
This commit is contained in:
R-Goc 2025-04-11 22:14:59 +02:00
parent ef59ecd9f3
commit ed654a8fb9
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3 changed files with 57 additions and 32 deletions
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1
AK/CMakeLists.txt
View file

@ -73,4 +73,5 @@ endif()
if (WIN32)
# FIXME: Windows on ARM
target_link_libraries(AK PRIVATE clang_rt.builtins-x86_64.lib)
target_link_libraries(AK PRIVATE Bcrypt.lib)
endif()

55
AK/Random.cpp
View file

@ -4,12 +4,67 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Platform.h>
#include <AK/Random.h>
#include <AK/UFixedBigInt.h>
#include <AK/UFixedBigIntDivision.h>
#if defined(AK_OS_WINDOWS)
# include <AK/NumericLimits.h>
# include <AK/Windows.h>
# include <bcrypt.h>
# include <ntstatus.h>
#endif
namespace AK {
// NOTE: This function is supposed to always give a random number. If possible it is of good quality, but it can fall
// back to rand() if it fails on some systems. For high speed you should probably use a different generator.
// See MathObject::random() from LibJS. Where cryptographic security is needed use LibCrypto/SecureRandom.h.
void fill_with_random([[maybe_unused]] Bytes bytes)
{
#if defined(AK_OS_SERENITY) || defined(AK_OS_ANDROID) || defined(AK_OS_BSD_GENERIC) || defined(AK_OS_HAIKU) || AK_LIBC_GLIBC_PREREQ(2, 36)
arc4random_buf(bytes.data(), bytes.size());
#elif defined(OSS_FUZZ)
#else
auto fill_with_random_fallback = [&]() {
for (auto& byte : bytes)
byte = rand();
};
# if defined(__unix__)
// The maximum permitted value for the getentropy length argument.
static constexpr size_t getentropy_length_limit = 256;
auto iterations = bytes.size() / getentropy_length_limit;
for (size_t i = 0; i < iterations; ++i) {
if (getentropy(bytes.data(), getentropy_length_limit) != 0) {
fill_with_random_fallback();
return;
}
bytes = bytes.slice(getentropy_length_limit);
}
if (bytes.is_empty() || getentropy(bytes.data(), bytes.size()) == 0)
return;
# elif defined(AK_OS_WINDOWS)
if (bytes.size() > NumericLimits<u32>::max()) [[unlikely]] {
fill_with_random_fallback();
return;
}
// NOTE: This is more secure than needed. But on modern hardware it be should more than fast enough.
NTSTATUS result = ::BCryptGenRandom(NULL, bytes.data(), bytes.size(), BCRYPT_USE_SYSTEM_PREFERRED_RNG);
if (result == STATUS_SUCCESS)
return;
# endif
fill_with_random_fallback();
#endif
}
u32 get_random_uniform(u32 max_bounds)
{
// If we try to divide all 2**32 numbers into groups of "max_bounds" numbers, we may end up

33
AK/Random.h
View file

@ -18,38 +18,7 @@
namespace AK {
inline void fill_with_random([[maybe_unused]] Bytes bytes)
{
#if defined(AK_OS_SERENITY) || defined(AK_OS_ANDROID) || defined(AK_OS_BSD_GENERIC) || defined(AK_OS_HAIKU) || AK_LIBC_GLIBC_PREREQ(2, 36)
arc4random_buf(bytes.data(), bytes.size());
#elif defined(OSS_FUZZ)
#else
auto fill_with_random_fallback = [&]() {
for (auto& byte : bytes)
byte = rand();
};
# if defined(__unix__)
// The maximum permitted value for the getentropy length argument.
static constexpr size_t getentropy_length_limit = 256;
auto iterations = bytes.size() / getentropy_length_limit;
for (size_t i = 0; i < iterations; ++i) {
if (getentropy(bytes.data(), getentropy_length_limit) != 0) {
fill_with_random_fallback();
return;
}
bytes = bytes.slice(getentropy_length_limit);
}
if (bytes.is_empty() || getentropy(bytes.data(), bytes.size()) == 0)
return;
# endif
fill_with_random_fallback();
#endif
}
void fill_with_random([[maybe_unused]] Bytes bytes);
template<typename T>
inline T get_random()