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// Copyright 2018 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/platform_shared_memory_region.h"
#include <sys/mman.h>
#include "base/posix/eintr_wrapper.h"
#include "third_party/ashmem/ashmem.h"
namespace base {
namespace subtle {
// For Android, we use ashmem to implement SharedMemory. ashmem_create_region
// will automatically pin the region. We never explicitly call pin/unpin. When
// all the file descriptors from different processes associated with the region
// are closed, the memory buffer will go away.
namespace {
static int GetAshmemRegionProtectionMask(int fd) {
int prot = ashmem_get_prot_region(fd);
if (prot < 0) {
DPLOG(ERROR) << "ashmem_get_prot_region failed";
return -1;
}
return prot;
}
} // namespace
// static
PlatformSharedMemoryRegion PlatformSharedMemoryRegion::Take(
ScopedFD fd,
Mode mode,
size_t size,
const UnguessableToken& guid) {
if (!fd.is_valid())
return {};
if (size == 0)
return {};
if (size > static_cast<size_t>(std::numeric_limits<int>::max()))
return {};
CHECK(CheckPlatformHandlePermissionsCorrespondToMode(fd.get(), mode, size));
return PlatformSharedMemoryRegion(std::move(fd), mode, size, guid);
}
int PlatformSharedMemoryRegion::GetPlatformHandle() const {
return handle_.get();
}
bool PlatformSharedMemoryRegion::IsValid() const {
return handle_.is_valid();
}
PlatformSharedMemoryRegion PlatformSharedMemoryRegion::Duplicate() const {
if (!IsValid())
return {};
CHECK_NE(mode_, Mode::kWritable)
<< "Duplicating a writable shared memory region is prohibited";
ScopedFD duped_fd(HANDLE_EINTR(dup(handle_.get())));
if (!duped_fd.is_valid()) {
DPLOG(ERROR) << "dup(" << handle_.get() << ") failed";
return {};
}
return PlatformSharedMemoryRegion(std::move(duped_fd), mode_, size_, guid_);
}
bool PlatformSharedMemoryRegion::ConvertToReadOnly() {
if (!IsValid())
return false;
CHECK_EQ(mode_, Mode::kWritable)
<< "Only writable shared memory region can be converted to read-only";
ScopedFD handle_copy(handle_.release());
int prot = GetAshmemRegionProtectionMask(handle_copy.get());
if (prot < 0)
return false;
prot &= ~PROT_WRITE;
int ret = ashmem_set_prot_region(handle_copy.get(), prot);
if (ret != 0) {
DPLOG(ERROR) << "ashmem_set_prot_region failed";
return false;
}
handle_ = std::move(handle_copy);
mode_ = Mode::kReadOnly;
return true;
}
bool PlatformSharedMemoryRegion::ConvertToUnsafe() {
if (!IsValid())
return false;
CHECK_EQ(mode_, Mode::kWritable)
<< "Only writable shared memory region can be converted to unsafe";
mode_ = Mode::kUnsafe;
return true;
}
bool PlatformSharedMemoryRegion::MapAt(off_t offset,
size_t size,
void** memory,
size_t* mapped_size) const {
if (!IsValid())
return false;
size_t end_byte;
if (!CheckAdd(offset, size).AssignIfValid(&end_byte) || end_byte > size_) {
return false;
}
bool write_allowed = mode_ != Mode::kReadOnly;
*memory = mmap(nullptr, size, PROT_READ | (write_allowed ? PROT_WRITE : 0),
MAP_SHARED, handle_.get(), offset);
bool mmap_succeeded = *memory && *memory != reinterpret_cast<void*>(-1);
if (!mmap_succeeded) {
DPLOG(ERROR) << "mmap " << handle_.get() << " failed";
return false;
}
*mapped_size = size;
DCHECK_EQ(0U,
reinterpret_cast<uintptr_t>(*memory) & (kMapMinimumAlignment - 1));
return true;
}
// static
PlatformSharedMemoryRegion PlatformSharedMemoryRegion::Create(Mode mode,
size_t size) {
if (size == 0)
return {};
if (size > static_cast<size_t>(std::numeric_limits<int>::max()))
return {};
CHECK_NE(mode, Mode::kReadOnly) << "Creating a region in read-only mode will "
"lead to this region being non-modifiable";
UnguessableToken guid = UnguessableToken::Create();
// trace_event is not supported in libchrome. To avoid includes of more
// trace_event code by base/memory/shared_memory_tracker.h, replace
// SharedMemoryTracker::GetDumpNameForTracing by the actual implementation.
ScopedFD fd(ashmem_create_region(
("shared_memory/"+guid.ToString()).c_str(), size));
if (!fd.is_valid()) {
DPLOG(ERROR) << "ashmem_create_region failed";
return {};
}
int err = ashmem_set_prot_region(fd.get(), PROT_READ | PROT_WRITE);
if (err < 0) {
DPLOG(ERROR) << "ashmem_set_prot_region failed";
return {};
}
return PlatformSharedMemoryRegion(std::move(fd), mode, size, guid);
}
bool PlatformSharedMemoryRegion::CheckPlatformHandlePermissionsCorrespondToMode(
PlatformHandle handle,
Mode mode,
size_t size) {
int prot = GetAshmemRegionProtectionMask(handle);
if (prot < 0)
return false;
bool is_read_only = (prot & PROT_WRITE) == 0;
bool expected_read_only = mode == Mode::kReadOnly;
if (is_read_only != expected_read_only) {
DLOG(ERROR) << "Ashmem region has a wrong protection mask: it is"
<< (is_read_only ? " " : " not ") << "read-only but it should"
<< (expected_read_only ? " " : " not ") << "be";
return false;
}
return true;
}
PlatformSharedMemoryRegion::PlatformSharedMemoryRegion(
ScopedFD fd,
Mode mode,
size_t size,
const UnguessableToken& guid)
: handle_(std::move(fd)), mode_(mode), size_(size), guid_(guid) {}
} // namespace subtle
} // namespace base
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