gsc – Gramine Shielded Containers¶
gsc COMMAND [OPTIONS] …
Docker containers are widely used to deploy applications in the cloud. Using Gramine Shielded Containers (GSC) we provide the infrastructure to deploy Docker containers protected by Intel SGX enclaves using the Gramine Library OS.
The gsc tool transforms a Docker image into a new image
gsc-<image-name>) which includes the Gramine Library OS, manifest
files, Intel SGX related information, and executes the application inside an
Intel SGX enclave using the Gramine Library OS. It follows the common Docker
approach to first build an image and subsequently run a container of an image.
At first a Docker image has to be graminized via the gsc build
command. When the graminized image should run within an Intel SGX enclave, the
image has to be signed via a gsc sign-image command. Subsequently,
the image can be run using docker run.
The installation descriptions of prerequisites are for Ubuntu 18.04 and may differ when using a different Ubuntu version or Linux distribution.
Please install the
python3-pip packages. In
addition, install the Docker client, Jinja2, TOML, and YAML python packages via
pip. GSC requires Python 3.6 or later.
sudo apt-get install docker.io python3 python3-pip pip3 install docker jinja2 toml pyyaml
SGX software stack¶
To run with Intel SGX, please install the corresponding software stack as described in https://gramine.readthedocs.io/en/latest/building.html.
To create Docker images, the user must have access to Docker daemon.
Please use this step with caution. By granting the user access to the Docker group, the user may acquire root privileges via docker run.
sudo adduser $USER docker
Create a configuration file called
config.yaml or specify a different
configuration file via gsc option. Please see the documentation on
configuration options below and use the
Command line arguments¶
gsc build – build graminized image¶
Builds an unsigned graminized Docker image of an application image called
gsc-<IMAGE-NAME>-unsigned by compiling Gramine or relying on a prebuilt
gsc build [OPTIONS] <IMAGE-NAME> <APP.MANIFEST>
Compile Gramine with debug flags and debug output. If configured to use a prebuilt Gramine image, the image has to support this option.
Compile Gramine with Linux PAL in addition to Linux-SGX PAL. If configured to use a prebuilt Gramine image, the image has to support this option.
Allow untrusted arguments to be specified at docker run. Otherwise any arguments specified during docker run are ignored.
Disable Docker’s caches during gsc build. This builds the unsigned graminized image from scratch.
Remove intermediate Docker images created by gsc build, if the image build is successful.
Set build-time variables during gsc build (same as docker build –build-arg).
Specify configuration file. Default:
Name of the application Docker image.
Manifest file (Gramine configuration).
gsc sign-image – signs a graminized image¶
Signs the enclave of an unsigned graminized Docker image and creates a new
Docker image called
gsc-<IMAGE-NAME>. gsc sign-image always
removes intermediate Docker images, if successful or not, to ensure the removal
of the signing key in them.
gsc sign-image [OPTIONS] <IMAGE-NAME> <KEY-FILE>
Specify configuration file. Default:
Name of the application Docker image
Used to sign the Intel SGX enclave
gsc build-gramine – build Gramine-only Docker image¶
Builds a base Docker image including the Gramine sources and compiled runtime. This base image can be used as input for gsc build via configuration parameter Gramine.Image.
gsc build-gramine [OPTIONS] <IMAGE-NAME>
Compile Gramine with debug flags and debug output. Allows gsc build commands to include debug runtime using
Compile Gramine with Linux PAL in addition to Linux-SGX PAL. Allows gsc build commands to include the Linux PAL using
Disable Docker’s caches during gsc build-gramine. This builds the unsigned graminized image from scratch.
Remove intermediate Docker images created by gsc build-gramine, if the image build is successful.
Set build-time variables during gsc build-gramine (same as docker build –build-arg).
Specify configuration file. Default:
Stop after Dockerfile is created and do not build the Docker image.
Name of the resulting Gramine Docker image
gsc info-image – retrieve information about graminized Docker image¶
Retrieves Intel SGX relevant information about the graminized Docker image such
MRSIGNER measurements for each application in the
gsc info-image <IMAGE-NAME>
Name of the graminized Docker image
Using Gramine’s trusted command line arguments¶
Most executables aren’t designed to run with attacker-controlled arguments. Allowing an attacker to control executable arguments can break the security of the resulting enclave.
gsc build uses the existing Docker image’s entrypoint and cmd fields
to identify the trusted arguments. These arguments are stored in
trusted_argv. This file is only generated when
--insecure-args is not specified. As a result any arguments
specified during docker run are ignored.
To be able to provide arguments at runtime, the image build has to enable this
via the option
Stages of building graminized SGX Docker images¶
The build process of a graminized Docker image from image
follows three main stages and produces an image named
gsc build-gramine performs only the first stage,
gsc build performs the first two stages, and finally
gsc sign-image performs the last stage.
- Building Gramine. The first stage builds Gramine from sources based on
the provided configuration (see
config.yaml) which includes the distribution (e.g., Ubuntu 18.04), Gramine repository, and the Intel SGX driver details. This stage can be skipped if gsc build uses a pre-built Gramine Docker image.
- Graminizing the application image. The second stage copies the important
Gramine artifacts (e.g., the runtime and signer tool) from the first stage
(or if the first stage was skipped, it pulls a prebuilt Docker image defined
via the configuration file). It then prepares image-specific variables such
as the executable path and the library path, and scans the entire image to
generate a list of trusted files. GSC excludes files and paths starting with
/var, since checksums are required which either don’t exist or may vary across different deployment machines. GSC combines these variables and list of trusted files into a new manifest file. In a last step the entrypoint is changed to launch the
apploader.shscript which generates an Intel SGX token and starts the gramine-sgx loader. Note that the generated image (
gsc-<image-name>-unsigned) cannot successfully load an Intel SGX enclave, since essential files and the signature of the enclave are still missing (see next stage).
- Signing the Intel SGX enclave. The third stage uses Gramine’s signer
tool to generate SIGSTRUCT files for SGX enclave initialization. This tool
also generates an SGX-specific manifest file. The required signing key is
provided by the user via the gsc sign-image command and copied
into this Docker build stage. The generated image is called
gsc-<image-name>and includes all necessary files to start an Intel SGX enclave.
In the future we plan to provide prebuilt Gramine images for popular cloud-provider offerings.
Generating a signed graminized Docker image¶
The last stage combines the graminized Docker image with the signed enclave and manifest files. Therefore it copies the SIGSTRUCT files and the SGX-specific manifest file from the previous stage into the graminized Docker image from the second stage.
GSC is configured via a configuration file called
specified as a gsc option. A template configuration file is provided
Defines Linux distribution to be used to build Gramine in. Currently tested distros are Ubuntu 18.04, Ubuntu 20.04, Ubuntu 21.04 and CentOS 8. Default value is
Defines the registry and repository where the Linux distribution image is located. Only needed if the image in Distro requires to be prepended with this information.
Source repository of Gramine. Default value: https://github.com/gramineproject/gramine.git.
Use this branch of the repository. Default value: master.
Builds graminized Docker image based on a prebuilt Gramine Docker image. These images are prepared via gsc build-gramine and will be provided for popular cloud-provider environments. Gramine.Repository and Gramine.Branch are ignored in case Gramine.Image is specified.
Source repository of the Intel SGX driver. Default value: “” (in-kernel driver)
Use this branch of the repository. Default value: “” (in-kernel driver)
Run graminized Docker images¶
Execute docker run command via Docker CLI and provide gsgx and isgx/sgx devices and the PSW/AESM socket. Additional Docker options and executable arguments may be supplied to the docker run command.
Forwarding devices to a container lowers security of the host. GSC should never be used as a sandbox for applications (i.e. it only shields the app from the host but not vice versa).
docker run [OPTIONS] gsc-<IMAGE-NAME> [<ARGUMENTS>]
docker run options. Common options include
-it(interactive with terminal),
--device(forward device). Please see Docker manual for details.
Name of original image (without GSC build).
Arguments to be supplied to the executable launching inside the Docker container and Gramine. Such arguments may only be provided when
--insecure-argswas specified during gsc build.
Execute with Linux PAL instead of Linux-SGX PAL¶
-L during GSC gsc build,
you may select the Linux PAL at Docker run time instead of the Linux-SGX PAL by
specifying the environment variable
GSC_PAL as an option to the
docker run command. When using the Linux PAL, it is not necessary to
sign the image via a gsc sign-image command.
This environment variable specifies the pal loader.
GSC requires a custom seccomp profile while running with Linux PAL, which has to be specified at Docker run time. There are two options:
Pass unconfined to run the container without the default seccomp profile. This option is generally considered insecure, since this results in containers running with unrestricted system calls (all system calls are allowed which increases the attack surface of the Linux Kernel).
Pass the custom seccomp profile https://github.com/gramineproject/gramine/blob/master/Scripts/docker_seccomp.json.
With this option, Docker containers restrict themselves to a rather narrow set of allowed system calls, keeping the attack surface of the Linux kernel small. All the necessary capabilities required for GSC to function are still enabled.
docker run ... --env GSC_PAL=Linux --security-opt seccomp=<profile> gsc-<image-name> ...
Example below relies on insecure arguments to be able to run Python with arbitrary arguments. This is not intended for production environments.
The example below shows how to graminize the public Docker image of Python3. This example assumes that all prerequisites are installed and configured.
Create a configuration file:
cp config.yaml.template config.yaml # Manually adopt config.yaml to the installed Intel SGX driver and desired # Gramine repository/version.
Generate the signing key (if you don’t already have a key):
openssl genrsa -3 -out enclave-key.pem 3072
Pull public Python image from Dockerhub:
docker pull python
Graminize the Python image using gsc build:
./gsc build --insecure-args python test/generic.manifest
Sign the graminized Docker image using gsc sign-image:
./gsc sign-image python enclave-key.pem
Retrieve SGX-related information from graminized image using gsc info-image:
./gsc info-image gsc-python
Test the graminized Docker image (change
--device=/dev/sgx_enclaveto your version of the Intel SGX driver if needed):
docker run --device=/dev/sgx_enclave \ -v /var/run/aesmd/aesm.socket:/var/run/aesmd/aesm.socket \ gsc-python -c 'print("HelloWorld!")'
You can also start a Bash interactive session in the graminized Docker image (useful for debugging):
docker run --device=/dev/sgx_enclave \ -v /var/run/aesmd/aesm.socket:/var/run/aesmd/aesm.socket \ -it --entrypoint /bin/bash gsc-python
This document focuses on the most important limitations of GSC. Issue #13 provides the complete list of known limitations and serves as a discussion board for workarounds.
Operating System dependency¶
GSC relies on Gramine to execute Linux applications inside Intel SGX enclaves and
the installation of prerequisites depends on package manager and package
repositories. Docker images based on Ubuntu and CentOS are supported by GSC.
GSC can simply be extended to support other distributions by
providing a set of templates for this distribution in
Trusted data in Docker volumes¶
Data mounted as Docker volumes at runtime is not included in the general search for trusted files during the image build. As a result, Gramine denies access to these files, since they are neither allowed nor trusted files. This will likely break applications using files stored in Docker volumes.
Trusted files can be added to image-specific manifest file (first argument to gsc build command) at build time. This workaround does not allow these files to change between build and run, or over multiple runs. This only provides integrity for files and not confidentiality.
Allowing dynamic file contents via Gramine protected files¶
Docker volumes can include Gramine protected files. As a result Gramine can open these protected files without knowing the exact contents as long as the protected file was configured in the manifest. The complete and secure use of protected files may require additional steps.
Integration of Docker Secrets¶
Docker Secrets are automatically pulled by Docker and the results are stored either in environment variables or mounted as files. GSC is currently unaware of such files and hence, cannot mark them trusted. Similar to trusted data, these files may be added to the manifest.
Access to files in excluded paths¶
The manifest generation excludes all files and paths starting with
/var from the list of
trusted files. If your application relies on some files in these directories,
you must manually add them to the manifest:
sgx.trusted_files = [ "file:file1", "file:file2" ] or sgx.allowed_files = [ "file:file3", "file:file4" ]
Docker images with non-executables as entrypoint¶
Docker images may contain a script entrypoint which is not an ELF executable. gsc fails to recognize such entrypoints and fails during the image build. A workaround relies on creating an image from the application image which has an entrypoint of the script interpreter with the script as an argument. This allows gsc to start the interpreter instead of the script.