| /* |
| * 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 "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 |