base/memory/shared_memory_mac.cc

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/memory/shared_memory.h"

#include <errno.h>
#include <fcntl.h>
#include <mach/mach_vm.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

#include "base/files/file_util.h"
#include "base/files/scoped_file.h"
#include "base/logging.h"
#include "base/mac/mac_util.h"
#include "base/mac/scoped_mach_vm.h"
#include "base/metrics/field_trial.h"
#include "base/metrics/histogram_macros.h"
#include "base/posix/eintr_wrapper.h"
#include "base/posix/safe_strerror.h"
#include "base/process/process_metrics.h"
#include "base/profiler/scoped_tracker.h"
#include "base/scoped_generic.h"
#include "base/strings/utf_string_conversions.h"

#if defined(OS_MACOSX)
#include "base/mac/foundation_util.h"
#endif  // OS_MACOSX

namespace base {

namespace {

const char kTrialName[] = "MacMemoryMechanism";
const char kTrialMach[] = "Mach";
const char kTrialPosix[] = "Posix";

SharedMemoryHandle::Type GetABTestMechanism() {
  static bool found_group = false;
  static SharedMemoryHandle::Type group = SharedMemoryHandle::MACH;

  if (found_group)
    return group;

  const std::string group_name =
      base::FieldTrialList::FindFullName(kTrialName);
  if (group_name == kTrialMach) {
    group = SharedMemoryHandle::MACH;
    found_group = true;
  } else if (group_name == kTrialPosix) {
    group = SharedMemoryHandle::POSIX;
    found_group = true;
  } else {
    group = SharedMemoryHandle::MACH;
  }

  return group;
}

// Emits a histogram entry indicating which type of SharedMemory was created.
void EmitMechanism(SharedMemoryHandle::Type type) {
  UMA_HISTOGRAM_ENUMERATION("OSX.SharedMemory.Mechanism", type,
                            SharedMemoryHandle::TypeMax);
}

// Returns whether the operation succeeded.
// |new_handle| is an output variable, populated on success. The caller takes
// ownership of the underlying memory object.
// |handle| is the handle to copy.
// If |handle| is already mapped, |mapped_addr| is its mapped location.
// Otherwise, |mapped_addr| should be |nullptr|.
bool MakeMachSharedMemoryHandleReadOnly(SharedMemoryHandle* new_handle,
                                        SharedMemoryHandle handle,
                                        void* mapped_addr) {
  if (!handle.IsValid())
    return false;

  size_t size;
  CHECK(handle.GetSize(&size));

  // Map if necessary.
  void* temp_addr = mapped_addr;
  base::mac::ScopedMachVM scoper;
  if (!temp_addr) {
    // Intentionally lower current prot and max prot to |VM_PROT_READ|.
    kern_return_t kr = mach_vm_map(
        mach_task_self(), reinterpret_cast<mach_vm_address_t*>(&temp_addr),
        size, 0, VM_FLAGS_ANYWHERE, handle.GetMemoryObject(), 0, FALSE,
        VM_PROT_READ, VM_PROT_READ, VM_INHERIT_NONE);
    if (kr != KERN_SUCCESS)
      return false;
    scoper.reset(reinterpret_cast<vm_address_t>(temp_addr),
                 mach_vm_round_page(size));
  }

  // Make new memory object.
  mach_port_t named_right;
  kern_return_t kr = mach_make_memory_entry_64(
      mach_task_self(), reinterpret_cast<memory_object_size_t*>(&size),
      reinterpret_cast<memory_object_offset_t>(temp_addr), VM_PROT_READ,
      &named_right, MACH_PORT_NULL);
  if (kr != KERN_SUCCESS)
    return false;

  *new_handle = SharedMemoryHandle(named_right, size, base::GetCurrentProcId());
  return true;
}

struct ScopedPathUnlinkerTraits {
  static FilePath* InvalidValue() { return nullptr; }

  static void Free(FilePath* path) {
    // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "466437 SharedMemory::Create::Unlink"));
    if (unlink(path->value().c_str()))
      PLOG(WARNING) << "unlink";
  }
};

// Unlinks the FilePath when the object is destroyed.
typedef ScopedGeneric<FilePath*, ScopedPathUnlinkerTraits> ScopedPathUnlinker;

// Makes a temporary file, fdopens it, and then unlinks it. |fp| is populated
// with the fdopened FILE. |readonly_fd| is populated with the opened fd if
// options.share_read_only is true. |path| is populated with the location of
// the file before it was unlinked.
// Returns false if there's an unhandled failure.
bool CreateAnonymousSharedMemory(const SharedMemoryCreateOptions& options,
                                 ScopedFILE* fp,
                                 ScopedFD* readonly_fd,
                                 FilePath* path) {
  // Q: Why not use the shm_open() etc. APIs?
  // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
  FilePath directory;
  ScopedPathUnlinker path_unlinker;
  if (GetShmemTempDir(options.executable, &directory)) {
    // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "466437 SharedMemory::Create::OpenTemporaryFile"));
    fp->reset(CreateAndOpenTemporaryFileInDir(directory, path));

    // Deleting the file prevents anyone else from mapping it in (making it
    // private), and prevents the need for cleanup (once the last fd is
    // closed, it is truly freed).
    if (*fp)
      path_unlinker.reset(path);
  }

  if (*fp) {
    if (options.share_read_only) {
      // TODO(erikchen): Remove ScopedTracker below once
      // http://crbug.com/466437 is fixed.
      tracked_objects::ScopedTracker tracking_profile(
          FROM_HERE_WITH_EXPLICIT_FUNCTION(
              "466437 SharedMemory::Create::OpenReadonly"));
      // Also open as readonly so that we can ShareReadOnlyToProcess.
      readonly_fd->reset(HANDLE_EINTR(open(path->value().c_str(), O_RDONLY)));
      if (!readonly_fd->is_valid()) {
        DPLOG(ERROR) << "open(\"" << path->value() << "\", O_RDONLY) failed";
        fp->reset();
        return false;
      }
    }
  }
  return true;
}

}  // namespace

SharedMemoryCreateOptions::SharedMemoryCreateOptions()
    : type(SharedMemoryHandle::MACH),
      size(0),
      executable(false),
      share_read_only(false) {
  if (mac::IsOSLionOrLater()) {
    // A/B test the mechanism. Once the experiment is over, this will always be
    // set to SharedMemoryHandle::MACH.
    // http://crbug.com/547261
    type = GetABTestMechanism();
  } else {
    // Mach shared memory isn't supported on OSX 10.6 or older.
    type = SharedMemoryHandle::POSIX;
  }
}

SharedMemory::SharedMemory()
    : mapped_memory_mechanism_(SharedMemoryHandle::POSIX),
      readonly_mapped_file_(-1),
      mapped_size_(0),
      memory_(NULL),
      read_only_(false),
      requested_size_(0) {}

SharedMemory::SharedMemory(const SharedMemoryHandle& handle, bool read_only)
    : shm_(handle),
      mapped_memory_mechanism_(SharedMemoryHandle::POSIX),
      readonly_mapped_file_(-1),
      mapped_size_(0),
      memory_(NULL),
      read_only_(read_only),
      requested_size_(0) {}

SharedMemory::SharedMemory(const SharedMemoryHandle& handle,
                           bool read_only,
                           ProcessHandle process)
    : mapped_memory_mechanism_(SharedMemoryHandle::POSIX),
      readonly_mapped_file_(-1),
      mapped_size_(0),
      memory_(NULL),
      read_only_(read_only),
      requested_size_(0) {
  // We don't handle this case yet (note the ignored parameter); let's die if
  // someone comes calling.
  NOTREACHED();
}

SharedMemory::~SharedMemory() {
  Unmap();
  Close();
}

// static
bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
  return handle.IsValid();
}

// static
SharedMemoryHandle SharedMemory::NULLHandle() {
  return SharedMemoryHandle();
}

// static
void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
  handle.Close();
}

// static
size_t SharedMemory::GetHandleLimit() {
  return GetMaxFds();
}

// static
SharedMemoryHandle SharedMemory::DuplicateHandle(
    const SharedMemoryHandle& handle) {
  return handle.Duplicate();
}

// static
int SharedMemory::GetFdFromSharedMemoryHandle(
    const SharedMemoryHandle& handle) {
  return handle.GetFileDescriptor().fd;
}

bool SharedMemory::CreateAndMapAnonymous(size_t size) {
  return CreateAnonymous(size) && Map(size);
}

bool SharedMemory::CreateAndMapAnonymousPosix(size_t size) {
  return CreateAnonymousPosix(size) && Map(size);
}

bool SharedMemory::CreateAnonymousPosix(size_t size) {
  SharedMemoryCreateOptions options;
  options.type = SharedMemoryHandle::POSIX;
  options.size = size;
  return Create(options);
}

// static
bool SharedMemory::GetSizeFromSharedMemoryHandle(
    const SharedMemoryHandle& handle,
    size_t* size) {
  return handle.GetSize(size);
}

// Chromium mostly only uses the unique/private shmem as specified by
// "name == L"". The exception is in the StatsTable.
bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
  // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
  // is fixed.
  tracked_objects::ScopedTracker tracking_profile1(
      FROM_HERE_WITH_EXPLICIT_FUNCTION(
          "466437 SharedMemory::Create::Start"));
  DCHECK(!shm_.IsValid());
  if (options.size == 0) return false;

  if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
    return false;

  EmitMechanism(options.type);

  if (options.type == SharedMemoryHandle::MACH) {
    shm_ = SharedMemoryHandle(options.size);
    requested_size_ = options.size;
    return shm_.IsValid();
  }

  // This function theoretically can block on the disk. Both profiling of real
  // users and local instrumentation shows that this is a real problem.
  // https://code.google.com/p/chromium/issues/detail?id=466437
  base::ThreadRestrictions::ScopedAllowIO allow_io;

  ScopedFILE fp;
  ScopedFD readonly_fd;

  FilePath path;
  bool result = CreateAnonymousSharedMemory(options, &fp, &readonly_fd, &path);
  if (!result)
    return false;

  if (!fp) {
    PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
    return false;
  }

  // Get current size.
  struct stat stat;
  if (fstat(fileno(fp.get()), &stat) != 0)
    return false;
  const size_t current_size = stat.st_size;
  if (current_size != options.size) {
    if (HANDLE_EINTR(ftruncate(fileno(fp.get()), options.size)) != 0)
      return false;
  }
  requested_size_ = options.size;

  return PrepareMapFile(std::move(fp), std::move(readonly_fd));
}

bool SharedMemory::MapAt(off_t offset, size_t bytes) {
  if (!shm_.IsValid())
    return false;
  if (bytes > static_cast<size_t>(std::numeric_limits<int>::max()))
    return false;
  if (memory_)
    return false;

  bool success = shm_.MapAt(offset, bytes, &memory_, read_only_);
  if (success) {
    mapped_size_ = bytes;
    DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
                      (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
    mapped_memory_mechanism_ = shm_.GetType();
  } else {
    memory_ = NULL;
  }

  return success;
}

bool SharedMemory::Unmap() {
  if (memory_ == NULL)
    return false;

  switch (mapped_memory_mechanism_) {
    case SharedMemoryHandle::POSIX:
      munmap(memory_, mapped_size_);
      break;
    case SharedMemoryHandle::MACH:
      mach_vm_deallocate(mach_task_self(),
                         reinterpret_cast<mach_vm_address_t>(memory_),
                         mapped_size_);
      break;
  }

  memory_ = NULL;
  mapped_size_ = 0;
  return true;
}

SharedMemoryHandle SharedMemory::handle() const {
  switch (shm_.GetType()) {
    case SharedMemoryHandle::POSIX:
      return SharedMemoryHandle(shm_.GetFileDescriptor().fd, false);
    case SharedMemoryHandle::MACH:
      return shm_;
  }
}

void SharedMemory::Close() {
  shm_.Close();
  shm_ = SharedMemoryHandle();
  if (shm_.GetType() == SharedMemoryHandle::POSIX) {
    if (readonly_mapped_file_ > 0) {
      if (IGNORE_EINTR(close(readonly_mapped_file_)) < 0)
        PLOG(ERROR) << "close";
      readonly_mapped_file_ = -1;
    }
  }
}

bool SharedMemory::PrepareMapFile(ScopedFILE fp, ScopedFD readonly_fd) {
  DCHECK(!shm_.IsValid());
  DCHECK_EQ(-1, readonly_mapped_file_);
  if (fp == NULL)
    return false;

  // This function theoretically can block on the disk, but realistically
  // the temporary files we create will just go into the buffer cache
  // and be deleted before they ever make it out to disk.
  base::ThreadRestrictions::ScopedAllowIO allow_io;

  struct stat st = {};
  if (fstat(fileno(fp.get()), &st))
    NOTREACHED();
  if (readonly_fd.is_valid()) {
    struct stat readonly_st = {};
    if (fstat(readonly_fd.get(), &readonly_st))
      NOTREACHED();
    if (st.st_dev != readonly_st.st_dev || st.st_ino != readonly_st.st_ino) {
      LOG(ERROR) << "writable and read-only inodes don't match; bailing";
      return false;
    }
  }

  int mapped_file = HANDLE_EINTR(dup(fileno(fp.get())));
  if (mapped_file == -1) {
    if (errno == EMFILE) {
      LOG(WARNING) << "Shared memory creation failed; out of file descriptors";
      return false;
    } else {
      NOTREACHED() << "Call to dup failed, errno=" << errno;
    }
  }
  shm_ = SharedMemoryHandle(mapped_file, false);
  readonly_mapped_file_ = readonly_fd.release();

  return true;
}

bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                        SharedMemoryHandle* new_handle,
                                        bool close_self,
                                        ShareMode share_mode) {
  if (shm_.GetType() == SharedMemoryHandle::MACH) {
    DCHECK(shm_.IsValid());

    bool success = false;
    switch (share_mode) {
      case SHARE_CURRENT_MODE:
        *new_handle = shm_.Duplicate();
        success = true;
        break;
      case SHARE_READONLY:
        success = MakeMachSharedMemoryHandleReadOnly(new_handle, shm_, memory_);
        break;
    }

    if (success)
      new_handle->SetOwnershipPassesToIPC(true);

    if (close_self) {
      Unmap();
      Close();
    }

    return success;
  }

  int handle_to_dup = -1;
  switch (share_mode) {
    case SHARE_CURRENT_MODE:
      handle_to_dup = shm_.GetFileDescriptor().fd;
      break;
    case SHARE_READONLY:
      // We could imagine re-opening the file from /dev/fd, but that can't make
      // it readonly on Mac: https://codereview.chromium.org/27265002/#msg10
      CHECK_GE(readonly_mapped_file_, 0);
      handle_to_dup = readonly_mapped_file_;
      break;
  }

  const int new_fd = HANDLE_EINTR(dup(handle_to_dup));
  if (new_fd < 0) {
    if (close_self) {
      Unmap();
      Close();
    }
    DPLOG(ERROR) << "dup() failed.";
    return false;
  }

  new_handle->SetFileHandle(new_fd, true);

  if (close_self) {
    Unmap();
    Close();
  }

  return true;
}

}  // namespace base