The Tor Browser: mfbt/Poison.h@97036ab72558

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

     1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */

     3 /* This Source Code Form is subject to the terms of the Mozilla Public

     4  * License, v. 2.0. If a copy of the MPL was not distributed with this

     5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     7 /*

     8  * A poison value that can be used to fill a memory space with

     9  * an address that leads to a safe crash when dereferenced.

    10  */

    12 #ifndef mozilla_Poison_h

    13 #define mozilla_Poison_h

    15 #include "mozilla/Assertions.h"

    16 #include "mozilla/Types.h"

    18 #include <stdint.h>

    20 MOZ_BEGIN_EXTERN_C

    22 extern MFBT_DATA uintptr_t gMozillaPoisonValue;

    24 /**

    25  * @return the poison value.

    26  */

    27 inline uintptr_t mozPoisonValue()

    28 {

    29   return gMozillaPoisonValue;

    30 }

    32 /**

    33  * Overwrite the memory block of aSize bytes at aPtr with the poison value.

    34  * aPtr MUST be aligned at a sizeof(uintptr_t) boundary.

    35  * Only an even number of sizeof(uintptr_t) bytes are overwritten, the last

    36  * few bytes (if any) is not overwritten.

    37  */

    38 inline void mozWritePoison(void* aPtr, size_t aSize)

    39 {

    40   const uintptr_t POISON = mozPoisonValue();

    41   char* p = (char*)aPtr;

    42   char* limit = p + aSize;

    43   MOZ_ASSERT((uintptr_t)aPtr % sizeof(uintptr_t) == 0, "bad alignment");

    44   MOZ_ASSERT(aSize >= sizeof(uintptr_t), "poisoning this object has no effect");

    45   for (; p < limit; p += sizeof(uintptr_t)) {

    46     *((uintptr_t*)p) = POISON;

    47   }

    48 }

    50 /**

    51  * Initialize the poison value.

    52  * This should only be called once.

    53  */

    54 extern MFBT_API void mozPoisonValueInit();

    56 /* Values annotated by CrashReporter */

    57 extern MFBT_DATA uintptr_t gMozillaPoisonBase;

    58 extern MFBT_DATA uintptr_t gMozillaPoisonSize;

    60 MOZ_END_EXTERN_C

    62 #endif /* mozilla_Poison_h */

The Tor Browser / file revision

mfbt/Poison.h@97036ab72558

mfbt/Poison.h