mirror of
https://github.com/classilla/tenfourfox.git
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211 lines
5.1 KiB
C++
211 lines
5.1 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* A poison value that can be used to fill a memory space with
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* an address that leads to a safe crash when dereferenced.
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*/
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#include "mozilla/Poison.h"
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#include "mozilla/Assertions.h"
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#ifdef _WIN32
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# include <windows.h>
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#elif !defined(__OS2__)
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# include <unistd.h>
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# include <sys/mman.h>
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# ifndef MAP_ANON
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# ifdef MAP_ANONYMOUS
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# define MAP_ANON MAP_ANONYMOUS
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# else
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# error "Don't know how to get anonymous memory"
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# endif
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# endif
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#endif
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extern "C" {
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uintptr_t gMozillaPoisonValue;
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uintptr_t gMozillaPoisonBase;
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uintptr_t gMozillaPoisonSize;
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}
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// Freed memory is filled with a poison value, which we arrange to
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// form a pointer either to an always-unmapped region of the address
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// space, or to a page that has been reserved and rendered
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// inaccessible via OS primitives. See tests/TestPoisonArea.cpp for
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// extensive discussion of the requirements for this page. The code
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// from here to 'class FreeList' needs to be kept in sync with that
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// file.
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#ifdef _WIN32
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static void*
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ReserveRegion(uintptr_t aRegion, uintptr_t aSize)
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{
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return VirtualAlloc((void*)aRegion, aSize, MEM_RESERVE, PAGE_NOACCESS);
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}
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static void
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ReleaseRegion(void* aRegion, uintptr_t aSize)
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{
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VirtualFree(aRegion, aSize, MEM_RELEASE);
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}
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static bool
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ProbeRegion(uintptr_t aRegion, uintptr_t aSize)
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{
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SYSTEM_INFO sinfo;
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GetSystemInfo(&sinfo);
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if (aRegion >= (uintptr_t)sinfo.lpMaximumApplicationAddress &&
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aRegion + aSize >= (uintptr_t)sinfo.lpMaximumApplicationAddress) {
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return true;
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} else {
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return false;
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}
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}
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static uintptr_t
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GetDesiredRegionSize()
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{
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SYSTEM_INFO sinfo;
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GetSystemInfo(&sinfo);
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return sinfo.dwAllocationGranularity;
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}
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#define RESERVE_FAILED 0
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#elif defined(__OS2__)
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static void*
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ReserveRegion(uintptr_t aRegion, uintptr_t aSize)
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{
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// OS/2 doesn't support allocation at an arbitrary address,
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// so return an address that is known to be invalid.
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return (void*)0xFFFD0000;
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}
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static void
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ReleaseRegion(void* aRegion, uintptr_t aSize)
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{
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return;
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}
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static bool
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ProbeRegion(uintptr_t aRegion, uintptr_t aSize)
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{
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// There's no reliable way to probe an address in the system
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// arena other than by touching it and seeing if a trap occurs.
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return false;
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}
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static uintptr_t
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GetDesiredRegionSize()
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{
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// Page size is fixed at 4k.
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return 0x1000;
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}
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#define RESERVE_FAILED 0
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#else // Unix
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#include "mozilla/TaggedAnonymousMemory.h"
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static void*
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ReserveRegion(uintptr_t aRegion, uintptr_t aSize)
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{
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return MozTaggedAnonymousMmap(reinterpret_cast<void*>(aRegion), aSize,
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PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0,
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"poison");
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}
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static void
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ReleaseRegion(void* aRegion, uintptr_t aSize)
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{
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munmap(aRegion, aSize);
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}
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static bool
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ProbeRegion(uintptr_t aRegion, uintptr_t aSize)
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{
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if (madvise(reinterpret_cast<void*>(aRegion), aSize, MADV_NORMAL)) {
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return true;
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} else {
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return false;
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}
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}
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static uintptr_t
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GetDesiredRegionSize()
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{
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return sysconf(_SC_PAGESIZE);
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}
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#define RESERVE_FAILED MAP_FAILED
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#endif // system dependencies
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static_assert(sizeof(uintptr_t) == 4 || sizeof(uintptr_t) == 8, "");
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static_assert(sizeof(uintptr_t) == sizeof(void*), "");
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static uintptr_t
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ReservePoisonArea(uintptr_t rgnsize)
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{
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if (sizeof(uintptr_t) == 8) {
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// Use the hardware-inaccessible region.
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// We have to avoid 64-bit constants and shifts by 32 bits, since this
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// code is compiled in 32-bit mode, although it is never executed there.
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return
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(((uintptr_t(0x7FFFFFFFu) << 31) << 1 | uintptr_t(0xF0DEAFFFu))
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& ~(rgnsize-1));
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}
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// First see if we can allocate the preferred poison address from the OS.
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uintptr_t candidate = (0xF0DEAFFF & ~(rgnsize-1));
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void* result = ReserveRegion(candidate, rgnsize);
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if (result == (void*)candidate) {
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// success - inaccessible page allocated
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return candidate;
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}
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// That didn't work, so see if the preferred address is within a range
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// of permanently inacessible memory.
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if (ProbeRegion(candidate, rgnsize)) {
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// success - selected page cannot be usable memory
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if (result != RESERVE_FAILED) {
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ReleaseRegion(result, rgnsize);
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}
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return candidate;
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}
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// The preferred address is already in use. Did the OS give us a
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// consolation prize?
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if (result != RESERVE_FAILED) {
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return uintptr_t(result);
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}
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// It didn't, so try to allocate again, without any constraint on
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// the address.
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result = ReserveRegion(0, rgnsize);
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if (result != RESERVE_FAILED) {
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return uintptr_t(result);
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}
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// no usable poison region identified
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MOZ_CRASH();
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return 0;
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}
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void
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mozPoisonValueInit()
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{
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gMozillaPoisonSize = GetDesiredRegionSize();
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gMozillaPoisonBase = ReservePoisonArea(gMozillaPoisonSize);
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if (gMozillaPoisonSize == 0) { // can't happen
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return;
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}
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gMozillaPoisonValue = gMozillaPoisonBase + gMozillaPoisonSize / 2 - 1;
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}
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