设备内存指纹

一、前端通过获取Navigator.deviceMemory来查询系统内存。

二、Navigator.deviceMemory

1、navigator_device_memory.idl接口定义：

// https://github.com/w3c/device-memory#the-web-exposed-apiinterface mixin NavigatorDeviceMemory {[HighEntropy=Direct,MeasureAs=NavigatorDeviceMemory,SecureContext]readonly attribute float deviceMemory;
};

2、v8_navigator

out\Debug\gen\third_party\blink\renderer\bindings\modules\v8\v8_navigator.cc

void DeviceMemoryAttributeGetCallback(const v8::FunctionCallbackInfo<v8::Value>& info) {RUNTIME_CALL_TIMER_SCOPE_DISABLED_BY_DEFAULT(info.GetIsolate(), "Blink_Navigator_deviceMemory_Getter");
BLINK_BINDINGS_TRACE_EVENT("Navigator.deviceMemory.get");
// [HighEntropy]
const Dactyloscoper::HighEntropyTracer  high_entropy_tracer("Navigator.deviceMemory.get", info);
v8::Isolate* isolate = info.GetIsolate();
v8::Local<v8::Context> current_context = isolate->GetCurrentContext();
ExecutionContext* current_execution_context = ExecutionContext::From(current_context);
// [Measure], [MeasureAs]
UseCounter::Count(current_execution_context, WebFeature::kNavigatorDeviceMemory);v8::Local<v8::Object> v8_receiver = info.This();
Navigator* blink_receiver = V8Navigator::ToWrappableUnsafe(isolate, v8_receiver);
auto&& return_value = blink_receiver->deviceMemory();
bindings::V8SetReturnValue(info, return_value, bindings::V8ReturnValue::PrimitiveType<float>());
// [HighEntropy=Direct]
Dactyloscoper::RecordDirectSurface(current_execution_context, WebFeature::kNavigatorDeviceMemory, return_value);
}

3、接口实现c++：

third_party\blink\renderer\core\frame\navigator_device_memory.h

third_party\blink\renderer\core\frame\navigator_device_memory.cc

namespace blink {float NavigatorDeviceMemory::deviceMemory() const {return ApproximatedDeviceMemory::GetApproximatedDeviceMemory();
}}  // namespace blink

third_party\blink\common\device_memory\approximated_device_memory.cc

namespace blink {// static
float ApproximatedDeviceMemory::approximated_device_memory_gb_ = 0.0;
int64_t ApproximatedDeviceMemory::physical_memory_mb_ = 0;// static
void ApproximatedDeviceMemory::Initialize() {if (approximated_device_memory_gb_ > 0.0)return;DCHECK_EQ(0, physical_memory_mb_);physical_memory_mb_ = ::base::SysInfo::AmountOfPhysicalMemoryMB();CalculateAndSetApproximatedDeviceMemory();
}// static
float ApproximatedDeviceMemory::GetApproximatedDeviceMemory() {return approximated_device_memory_gb_;
}// static
void ApproximatedDeviceMemory::CalculateAndSetApproximatedDeviceMemory() {// The calculations in this method are described in the specification:// https://w3c.github.io/device-memory/.DCHECK_GT(physical_memory_mb_, 0);int lower_bound = physical_memory_mb_;int power = 0;// Extract the most-significant-bit and its location.while (lower_bound > 1) {lower_bound >>= 1;power++;}// The remaining should always be equal to exactly 1.DCHECK_EQ(lower_bound, 1);int64_t upper_bound = lower_bound + 1;lower_bound = lower_bound << power;upper_bound = upper_bound << power;// Find the closest bound, and convert it to GB.if (physical_memory_mb_ - lower_bound <= upper_bound - physical_memory_mb_)approximated_device_memory_gb_ = static_cast<float>(lower_bound) / 1024.0;elseapproximated_device_memory_gb_ = static_cast<float>(upper_bound) / 1024.0;// Max-limit the reported value to 8GB to reduce fingerprintability of// high-spec machines.if (approximated_device_memory_gb_ > 8)approximated_device_memory_gb_ = 8.0;
}// static
void ApproximatedDeviceMemory::SetPhysicalMemoryMBForTesting(int64_t physical_memory_mb) {physical_memory_mb_ = physical_memory_mb;CalculateAndSetApproximatedDeviceMemory();
}}  // namespace blink