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// Copyright 2018 The Chromium Authors
// 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 <lib/zx/vmar.h>
#include <zircon/process.h>
#include <zircon/rights.h>
#include "base/bits.h"
#include "base/check_op.h"
#include "base/fuchsia/fuchsia_logging.h"
#include "base/memory/page_size.h"
#include "base/types/expected.h"
namespace base {
namespace subtle {
static constexpr int kNoWriteOrExec =
ZX_DEFAULT_VMO_RIGHTS &
~(ZX_RIGHT_WRITE | ZX_RIGHT_EXECUTE | ZX_RIGHT_SET_PROPERTY);
// static
expected<PlatformSharedMemoryRegion, PlatformSharedMemoryRegion::TakeError>
PlatformSharedMemoryRegion::TakeOrFail(zx::vmo handle,
Mode mode,
size_t size,
const UnguessableToken& guid) {
if (!handle.is_valid()) {
return {};
}
if (size == 0) {
return {};
}
if (size > static_cast<size_t>(std::numeric_limits<int>::max())) {
return {};
}
return CheckPlatformHandlePermissionsCorrespondToMode(zx::unowned_vmo(handle),
mode, size)
.transform([&] {
return PlatformSharedMemoryRegion(std::move(handle), mode, size, guid);
});
}
zx::unowned_vmo PlatformSharedMemoryRegion::GetPlatformHandle() const {
return zx::unowned_vmo(handle_);
}
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";
zx::vmo duped_handle;
zx_status_t status = handle_.duplicate(ZX_RIGHT_SAME_RIGHTS, &duped_handle);
if (status != ZX_OK) {
ZX_DLOG(ERROR, status) << "zx_handle_duplicate";
return {};
}
return PlatformSharedMemoryRegion(std::move(duped_handle), 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";
zx_status_t status = handle_.replace(kNoWriteOrExec, &handle_);
if (status != ZX_OK) {
ZX_DLOG(ERROR, status) << "zx_handle_replace";
return false;
}
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;
}
// static
PlatformSharedMemoryRegion PlatformSharedMemoryRegion::Create(Mode mode,
size_t size) {
if (size == 0) {
return {};
}
// Aligning may overflow so check that the result doesn't decrease.
size_t rounded_size = bits::AlignUp(size, GetPageSize());
if (rounded_size < size ||
rounded_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";
zx::vmo vmo;
zx_status_t status = zx::vmo::create(rounded_size, 0, &vmo);
if (status != ZX_OK) {
ZX_DLOG(ERROR, status) << "zx_vmo_create";
return {};
}
// TODO(crbug.com/40639453): Take base::Location from the caller and use it to
// generate the name here.
constexpr char kVmoName[] = "cr-shared-memory-region";
status = vmo.set_property(ZX_PROP_NAME, kVmoName, strlen(kVmoName));
ZX_DCHECK(status == ZX_OK, status);
const int kNoExecFlags = ZX_DEFAULT_VMO_RIGHTS & ~ZX_RIGHT_EXECUTE;
status = vmo.replace(kNoExecFlags, &vmo);
if (status != ZX_OK) {
ZX_DLOG(ERROR, status) << "zx_handle_replace";
return {};
}
return PlatformSharedMemoryRegion(std::move(vmo), mode, size,
UnguessableToken::Create());
}
// static
expected<void, PlatformSharedMemoryRegion::TakeError>
PlatformSharedMemoryRegion::CheckPlatformHandlePermissionsCorrespondToMode(
PlatformSharedMemoryHandle handle,
Mode mode,
size_t size) {
zx_info_handle_basic_t basic = {};
zx_status_t status = handle->get_info(ZX_INFO_HANDLE_BASIC, &basic,
sizeof(basic), nullptr, nullptr);
ZX_CHECK(status == ZX_OK, status) << "zx_object_get_info";
if (basic.type != ZX_OBJ_TYPE_VMO) {
return unexpected(TakeError::kNotVmo);
}
bool is_read_only = (basic.rights & (ZX_RIGHT_WRITE | ZX_RIGHT_EXECUTE)) == 0;
bool expected_read_only = mode == Mode::kReadOnly;
if (is_read_only != expected_read_only) {
return unexpected(expected_read_only ? TakeError::kExpectedReadOnlyButNot
: TakeError::kExpectedWritableButNot);
}
return ok();
}
PlatformSharedMemoryRegion::PlatformSharedMemoryRegion(
zx::vmo handle,
Mode mode,
size_t size,
const UnguessableToken& guid)
: handle_(std::move(handle)), mode_(mode), size_(size), guid_(guid) {}
} // namespace subtle
} // namespace base
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