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/*
* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021-2022, Brian Gianforcaro <bgianf@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Types.h>
#if defined(KERNEL)
# include <Kernel/StdLib.h>
#else
# include <string.h>
#endif
ALWAYS_INLINE void fast_u32_copy(u32* dest, u32 const* src, size_t count)
{
#if ARCH(X86_64)
asm volatile(
"rep movsl\n"
: "+S"(src), "+D"(dest), "+c"(count)::"memory");
#else
__builtin_memcpy(dest, src, count * 4);
#endif
}
ALWAYS_INLINE void fast_u32_fill(u32* dest, u32 value, size_t count)
{
#if ARCH(X86_64)
asm volatile(
"rep stosl\n"
: "=D"(dest), "=c"(count)
: "D"(dest), "c"(count), "a"(value)
: "memory");
#else
for (auto* p = dest; p < (dest + count); ++p) {
*p = value;
}
#endif
}
namespace AK {
inline void secure_zero(void* ptr, size_t size)
{
__builtin_memset(ptr, 0, size);
// The memory barrier is here to avoid the compiler optimizing
// away the memset when we rely on it for wiping secrets.
asm volatile("" ::
: "memory");
}
// Naive implementation of a constant time buffer comparison function.
// The goal being to not use any conditional branching so calls are
// guarded against potential timing attacks.
//
// See OpenBSD's timingsafe_memcmp for more advanced implementations.
inline bool timing_safe_compare(void const* b1, void const* b2, size_t len)
{
auto* c1 = static_cast<char const*>(b1);
auto* c2 = static_cast<char const*>(b2);
u8 res = 0;
for (size_t i = 0; i < len; i++) {
res |= c1[i] ^ c2[i];
}
// FIXME: !res can potentially inject branches depending
// on which toolchain is being used for compilation. Ideally
// we would use a more advanced algorithm.
return !res;
}
}
#if USING_AK_GLOBALLY
using AK::secure_zero;
using AK::timing_safe_compare;
#endif
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