/* * Copyright (C) 2017-2018 Apple Inc. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "config.h" #include <wtf/Poisoned.h> #include <wtf/CryptographicallyRandomNumber.h> namespace WTF { uintptr_t makePoison() { uintptr_t poison = 0; #if ENABLE(POISON) do { poison = cryptographicallyRandomNumber(); poison = (poison << 16) ^ (static_cast<uintptr_t>(cryptographicallyRandomNumber()) << 3); } while (!(poison >> 32)); // Ensure that bits 32-47 are not completely 0. // Ensure that the poisoned bits (pointer ^ poison) looks like a valid pointer. RELEASE_ASSERT(poison && !(poison >> 48)); // Ensure that the poisoned bits (pointer ^ poison) cannot be 0. This is so that the poisoned // bits can also be used for a normal zero check without needing to be decoded first. poison |= (1 << 2); // Ensure that the bottom 2 alignment bits are still 0 so that the poisoned bits will // still preserve the properties of a pointer where these bits are expected to be 0. // This allows the poisoned bits to be used in place of the pointer by clients that // rely on this property of pointers and sets flags in the low bits. // Note: a regular pointer has 3 alignment bits, but the poisoned bits need to use one // (see above). Hence, clients can only use 2 bits for flags. RELEASE_ASSERT(!(poison & 0x3)); #endif return poison; } } // namespace WTF