firefox/ipc/glue/SharedMemoryMapping.cpp

/* -*- 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/. */

/* This source code was derived from Chromium code, and as such is also subject
 * to the [Chromium license](ipc/chromium/src/LICENSE). */

#include "mozilla/ipc/SharedMemoryHandle.h"
#include "mozilla/ipc/SharedMemoryMapping.h"
#include "SharedMemoryPlatform.h"

#include "mozilla/Atomics.h"
#include "mozilla/CheckedInt.h"
#include "nsIMemoryReporter.h"

#ifdef FUZZING
#  include "mozilla/ipc/SharedMemoryFuzzer.h"
#endif

namespace mozilla::ipc::shared_memory {

class MappingReporter final : public nsIMemoryReporter {
  ~MappingReporter() = default;

 public:
  static Atomic<size_t> mapped;

  NS_DECL_THREADSAFE_ISUPPORTS

  NS_IMETHOD
  CollectReports(nsIHandleReportCallback* aHandleReport, nsISupports* aData,
                 bool aAnonymize) override {
    MOZ_COLLECT_REPORT(
        "shmem-mapped", KIND_OTHER, UNITS_BYTES, mapped,
        "Memory shared with other processes that is mapped into the address "
        "space.");

    return NS_OK;
  }
};

Atomic<size_t> MappingReporter::mapped;

NS_IMPL_ISUPPORTS(MappingReporter, nsIMemoryReporter)

static void RegisterMappingMemoryReporter() {
  static Atomic<bool> registered;
  if (registered.compareExchange(false, true)) {
    RegisterStrongMemoryReporter(new MappingReporter());
  }
}

MappingBase::MappingBase() = default;

MappingBase& MappingBase::operator=(MappingBase&& aOther) {
  // Swap members with `aOther`, and unmap that mapping.
  std::swap(aOther.mMemory, mMemory);
  std::swap(aOther.mSize, mSize);
  aOther.Unmap();
  return *this;
}

void* MappingBase::Address() const {
#ifdef FUZZING
  return SharedMemoryFuzzer::MutateSharedMemory(mMemory, mSize);
#else
  return mMemory;
#endif
}

bool MappingBase::Map(const HandleBase& aHandle, void* aFixedAddress,
                      bool aReadOnly) {
  // Invalid handles will fail and result in an invalid mapping.
  if (!aHandle) {
    return false;
  }
  // Verify that the handle size can be stored as a mapping size first
  // (otherwise it won't be possible to map in the address space and the Map
  // call will fail).
  CheckedInt<size_t> checkedSize(aHandle.Size());
  if (!checkedSize.isValid()) {
    MOZ_LOG_FMT(gSharedMemoryLog, LogLevel::Error,
                "handle size to map exceeds address space size");
    return false;
  }

  return MapSubregion(aHandle, /* aOffset */ 0, checkedSize.value(),
                      aFixedAddress, aReadOnly);
}

bool MappingBase::MapSubregion(const HandleBase& aHandle, uint64_t aOffset,
                               size_t aSize, void* aFixedAddress,
                               bool aReadOnly) {
  CheckedInt<uint64_t> endOffset(aOffset);
  endOffset += aSize;
  if (!endOffset.isValid() || endOffset.value() > aHandle.Size()) {
    MOZ_LOG_FMT(gSharedMemoryLog, LogLevel::Error,
                "cannot map region exceeding aHandle.Size()");
    return false;
  }

  RegisterMappingMemoryReporter();

  if (auto mem =
          Platform::Map(aHandle, aOffset, aSize, aFixedAddress, aReadOnly)) {
    mMemory = *mem;
    mSize = aSize;
    MappingReporter::mapped += mSize;
    return true;
  }
  return false;
}

void MappingBase::Unmap() {
  if (IsValid()) {
    Platform::Unmap(mMemory, mSize);

    MOZ_ASSERT(MappingReporter::mapped >= mSize,
               "Can't unmap more than mapped");
    MappingReporter::mapped -= mSize;
  }
  mMemory = nullptr;
  mSize = 0;
}

std::tuple<void*, size_t> MappingBase::Release() && {
  // NOTE: this doesn't reduce gShmemMapped since it _is_ still mapped memory
  // (and will be until the process terminates).
  return std::make_tuple(std::exchange(mMemory, nullptr),
                         std::exchange(mSize, 0));
}

MutableOrReadOnlyMapping::Mapping(const MutableHandle& aHandle,
                                  void* aFixedAddress)
    : mReadOnly(false) {
  Map(aHandle, aFixedAddress, false);
}

MutableOrReadOnlyMapping::Mapping(const ReadOnlyHandle& aHandle,
                                  void* aFixedAddress)
    : mReadOnly(true) {
  Map(aHandle, aFixedAddress, true);
}

MutableOrReadOnlyMapping::Mapping(MutableMapping&& aMapping)
    : MappingData(std::move(aMapping)), mReadOnly(false) {}

MutableOrReadOnlyMapping::Mapping(ReadOnlyMapping&& aMapping)
    : MappingData(std::move(aMapping)), mReadOnly(true) {}

// We still store the handle if `Map` fails: the user may want to get it back
// (for instance, if fixed-address mapping doesn't work they may try mapping
// without one).
FreezableMapping::Mapping(FreezableHandle&& aHandle, void* aFixedAddress)
    : mHandle(std::move(aHandle)) {
  Map(mHandle, aFixedAddress, false);
}

FreezableMapping::Mapping(FreezableHandle&& aHandle, uint64_t aOffset,
                          size_t aSize, void* aFixedAddress)
    : mHandle(std::move(aHandle)) {
  MapSubregion(mHandle, aOffset, aSize, aFixedAddress, false);
}

ReadOnlyHandle FreezableMapping::Freeze() && {
  return std::move(*this).Unmap().Freeze();
}

std::tuple<ReadOnlyHandle, MutableMapping>
FreezableMapping::FreezeWithMutableMapping() && {
  auto handle = std::move(mHandle);
  return std::make_tuple(std::move(handle).Freeze(),
                         ConvertMappingTo<Type::Mutable>(std::move(*this)));
}

FreezableHandle FreezableMapping::Unmap() && {
  auto handle = std::move(mHandle);
  *this = nullptr;
  return handle;
}

bool LocalProtect(char* aAddr, size_t aSize, Access aAccess) {
  return Platform::Protect(aAddr, aSize, aAccess);
}

void* FindFreeAddressSpace(size_t aSize) {
  return Platform::FindFreeAddressSpace(aSize);
}

size_t SystemPageSize() { return Platform::PageSize(); }

size_t SystemAllocationGranularity() {
  return Platform::AllocationGranularity();
}

size_t PageAlignedSize(size_t aMinimum) {
  const size_t pageSize = Platform::PageSize();
  size_t nPagesNeeded = size_t(ceil(double(aMinimum) / double(pageSize)));
  return pageSize * nPagesNeeded;
}

}  // namespace mozilla::ipc::shared_memory