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Using Visual Studio to Develop Enclave Applications for Linux

This walkthrough assumes that you are using Visual Studio on a Windows development machine, and want to develop enclaves for Linux. If you instead want to use Visual Studio Code on a development machine running either Windows or Linux, see the VS Code instructions.

Prerequisites

To install the Open Enclave Host-Verify SDK instead, see installation instructions for Ubuntu 16.04 or installation instructions for Ubuntu 18.04.

To develop Linux applications using a Windows development machine, you will need the following:

  • Visual Studio 2019 (Community edition, or any other edition)
  • "Linux development with C++" Visual Studio workload, installable via Tools -> Workloads -> Other Toolsets -> Linux Development with C++
  • NuGet Package Manager feature, installable via Tools -> Individual components -> Code tools -> NuGet Package Manager
  • Open Enclave Wizard - Preview Visual Studio extension, v0.7 or later. The extension can be installed via that marketplace link, or from within Visual Studio. (Do Extensions -> Manage Extensions -> Online -> search for "enclave".) You must restart Visual Studio after installing the extension.

You will also need a build machine running Ubuntu 16.04 (64-bit) or Ubuntu 18.04. This can be any of the following:

Ideally, the machine should be SGX capable (see instructions for determining the SGX support level if needed), but a non-SGX machine can still be used:

  • in simulation mode, or
  • if you would like to install the Open Enclave Host-Verify SDK and build evidence verification applications without enclaves.

On the Linux build machine, or after opening an ssh session into the VM:

Finally, configure Visual Studio with the address (or name) of your Linux build machine, via Tools -> Options -> Cross Platform -> Connection Manager -> Add. This step may take a minute or two, as Visual Studio will copy some files locally for use by IntelliSense.

Walkthrough: Creating a C/C++ Enclave Application

We will now walk through the process of creating a C/C++ application that uses an enclave.

  1. Create a new Linux application using File -> New -> Project and find the Linux console app template, which is called "Console App" (note: NOT the "Console App (.NET Core)") with the Linux keyword. (If it is not immediately visible, the template can be found under Installed -> Visual C++ -> Cross Platform -> Linux.) Give the project a name, LinuxApp for example. This will create a "Hello World" console application. Alternatively, if you already have such a Linux application using a Visual Studio project file (.vcxproj file), you can start from your existing application.
  2. Configure the application project to use your Linux build environment, by right clicking on the project in the Solution Explorer and selecting Properties -> Configuration Properties -> General -> Remote Build Machine, and explicitly set it to the build machine you configured in the Connection Manager. (Due to a current Visual Studio bug, this step is required even if the correct value is shown by default. In other words, make sure the connection is shown in bold.)
  3. Also update Configuration Properties -> Debugging -> Remote Debug Machine to your build machine, again due to a current Visual Studio 2019 bug. At this point, you should be able to build and debug the Hello World application. For further discussion, see the Linux debugging walkthrough.
  4. Create an enclave library project by right clicking on the solution in the Solution Explorer and selecting Add -> New Project -> Open Enclave TEE Project (Linux). (If it is not immediately visible, look under Installed -> Visual C++ -> Cross Platform -> Linux.) Give it a name, LinuxEnclave for example. This will create a sample enclave with an ecall_DoWorkInEnclave() method exposed to applications, that will simply call an ocall_DoWorkInHost() method that will be implemented in the application. In this walkthrough, we'll leave this project as is for now, but afterwards you can modify it as you like.
  5. Configure the enclave project to use your Linux build environment, as you did in step 2. At this point, the enclave would build, but cannot be run as the application doesn't invoke it yet.
  6. Import the enclave into your application project, by right clicking on the application project in the Solution Explorer and selecting Open Enclave Configuration -> Import Enclave, then navigate to and select the EDL file (YourEnclaveProjectName.edl) in your enclave project. This step will modify your application project settings and add some additional files to it, including a C file named YourEnclaveProjectName_host.c. This C file contains a sample_enclave_call() method that will load and call ecall_DoWorkInEnclave(), and also contains a sample implementation of a ocall_DoWorkInHost() method that just prints a message when called. Although the app could be compiled and run at this point, sample_enclave_call() is still not called from anywhere.
  7. Open the application's main.cpp (or if you are starting from another existing application, whatever file you want to invoke enclave code from), and add a call to sample_enclave_call(). For example, update the main.cpp file to look like this, where the extern C declaration is needed because main.cpp is a C++ file whereas the YourEnclaveProjectName_host.c file is a C file:
#include <cstdio>

extern "C" {
    void sample_enclave_call(void);
};

int main()
{
    printf("hello from LinuxApp!\n");
    sample_enclave_call();
    return 0;
}
  1. For the platform, use x64 or ARM, since Open Enclave currently only supports 64-bit enclaves.
  2. You can now set breakpoints in Visual Studio, e.g., inside ecall_DoWorkInEnclave() and inside ocall_DoWorkInHost() and run and debug the enclave application just like any other application.

The solution will have two configurations: Debug and Release.

Modifying the application

Once you have the basic application working, you can modify it as desired. For example, to define new APIs between the enclave and the application:

  1. Edit the YourProjectName.edl file. Define any trusted APIs (called "ECALLs") you want to call from your application in the trusted{} section, and in the untrusted{} section, define any application APIs (called "OCALLs") that you want to call from your enclave. Definitions must be described using the EDL file syntax.
  2. Edit the YourProjectName_ecalls.c file, and fill in implementations of the ECALL(s) you added.
  3. Edit your application sources and fill in implementations of the OCALL(s) you added.

Known Issues

  • Building Trusted Applications for TrustZone is not yet supported.