/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* * A poison value that can be used to fill a memory space with * an address that leads to a safe crash when dereferenced.
*/
/** * Overwrite the memory block of aSize bytes at aPtr with the poison value. * Only a multiple of sizeof(uintptr_t) bytes are overwritten, the last * few bytes (if any) are not overwritten.
*/ inlinevoid mozWritePoison(void* aPtr, size_t aSize) { const uintptr_t POISON = mozPoisonValue(); char* p = (char*)aPtr; char* limit = p + (aSize & ~(sizeof(uintptr_t) - 1));
MOZ_ASSERT(aSize >= sizeof(uintptr_t), "poisoning this object has no effect"); for (; p < limit; p += sizeof(uintptr_t)) {
memcpy(p, &POISON, sizeof(POISON));
}
}
/** * A version of CorruptionCanary that is suitable as a member of objects that * are statically allocated.
*/ class CorruptionCanaryForStatics { public:
constexpr CorruptionCanaryForStatics() : mValue(kCanarySet) {}
// This is required to avoid static constructor bloat.
~CorruptionCanaryForStatics() = default;
/** * This class is designed to cause crashes when various kinds of memory * corruption are observed. For instance, let's say we have a class C where we * suspect out-of-bounds writes to some members. We can insert a member of type * Poison near the members we suspect are being corrupted by out-of-bounds * writes. Or perhaps we have a class K we suspect is subject to use-after-free * violations, in which case it doesn't particularly matter where in the class * we add the member of type Poison. * * In either case, we then insert calls to Check() throughout the code. Doing * so enables us to narrow down the location where the corruption is occurring. * A pleasant side-effect of these additional Check() calls is that crash * signatures may become more regular, as crashes will ideally occur * consolidated at the point of a Check(), rather than scattered about at * various uses of the corrupted memory.
*/ class CorruptionCanary : public CorruptionCanaryForStatics { public:
constexpr CorruptionCanary() = default;
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