gsc – Gramine Shielded Containers¶
Synopsis¶
gsc COMMAND [OPTIONS] …
Description¶
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
(called 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.
NOTE: As part of the gsc build step, GSC generates the manifest file with a list of trusted files (files with integrity protection). This list contains hashes of all files present in the original Docker image. Therefore, GSC’s manifest creation capability depends on packaging of the original Docker image: if the original Docker image is bloated (contains unnecessary files), then the generated manifest will also be bloated. Though this doesn’t worsen security guarantees of Gramine/GSC, it may affect startup performance. Please exercise care in pulling in only the dependencies truly required for your Docker image.
Prerequisites¶
The installation descriptions of prerequisites are for Ubuntu 20.04 and may differ when using a different Ubuntu version or Linux distribution.
Software packages¶
Please install the docker.io
, python3
, 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 tomli tomli-w pyyaml
SGX software stack¶
To run with Intel SGX, please install the corresponding software stack as described in https://gramine.readthedocs.io/en/stable/devel/building.html.
Host configuration¶
To create Docker images, the user must have access to Docker daemon.
Warning
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 config.yaml.template
as
reference.
Command line arguments¶
-
--help
¶
Display usage.
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
Gramine image.
gsc build [OPTIONS] <IMAGE-NAME> <APP.MANIFEST>
-
-b
<buildtype>
,
--buildtype
<buildtype>
¶ Use <buildtype> value
release
,debug
ordebugoptimized
to compile Gramine in the corresponding mode. Default:release
.
-
--insecure-args
¶
Allow untrusted arguments to be specified at docker run. Otherwise any arguments specified during docker run are ignored.
-
--no-cache
¶
Disable Docker’s caches during gsc build. This builds the unsigned graminized image from scratch.
-
--rm
¶
Remove intermediate Docker images created by gsc build, if the image build is successful.
-
--build-arg
¶
Set build-time variables during gsc build (same as docker build –build-arg).
-
-c
¶
Specify configuration file. Default:
config.yaml
.
-
IMAGE-NAME
¶
Name of the application Docker image.
-
APP.MANIFEST
¶
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>
-
-c
¶
Specify configuration file. Default:
config.yaml
-
-p
¶
Provide passphrase for the enclave signing key (if applicable)
-
-D
,
--define
¶
Set image sign-time variables during gsc sign.
-
--remove-gramine-deps
¶
Remove Gramine dependencies that are not needed at runtime. This may have a negative side effect of removing even those dependencies that are actually needed by the original application. Use with care!
-
IMAGE-NAME
¶
Name of the application Docker image
-
KEY-FILE
¶
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>
-
-b
<buildtype>
,
--buildtype
<buildtype>
¶ Use <buildtype> value
release
,debug
ordebugoptimized
to compile Gramine in the corresponding mode. Default:release
.
-
--no-cache
¶
Disable Docker’s caches during gsc build-gramine. This builds the unsigned graminized image from scratch.
-
--rm
¶
Remove intermediate Docker images created by gsc build-gramine, if the image build is successful.
-
--build-arg
¶
Set build-time variables during gsc build-gramine (same as docker build –build-arg).
-
-c
¶
Specify configuration file. Default:
config.yaml
-
-f
¶
Stop after Dockerfile is created and do not build the Docker image.
-
IMAGE-NAME
¶
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
as the MRENCLAVE
and MRSIGNER
measurements for each application in the
Docker image.
Synopsis:
gsc info-image <IMAGE-NAME>
-
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 --insecure-args
.
Stages of building graminized SGX Docker images¶
The build process of a graminized Docker image from image <image-name>
follows three main stages and produces an image named gsc-<image-name>
.
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, 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 extracts image-specific environment
variables and scans the entire image to generate a list of trusted files. All
envvars are overridden (if duplicates found) in the following order: first
from a user-provided manifest, if not found then from the GSC-internal
manifest, and finally from the original Docker image environment. The only
exceptions are
LD_LIBRARY_PATH
,PATH
,LD_PRELOAD
; they are concatenated instead of overridden (concatenation order is the same as above). GSC excludes files and paths starting with/boot
,/dev
,.dockerenv
,.dockerinit
,/etc/mtab
,/etc/rc
,/proc
,/sys
, and/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 theapploader.sh
script which generates an Intel SGX token (only if needed, on non-FLC platforms) 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.
Configuration¶
GSC is configured via a configuration file called config.yaml
or
specified as a gsc option. A template configuration file is provided
in config.yaml.template
.
-
Distro
Defines Linux distribution to be used to build Gramine in. This distro should match the distro of the supplied Docker image; otherwise the results may be unpredictable. Currently supported distros are Ubuntu 20.04, Ubuntu 21.04, Ubuntu 22.04, Ubuntu 23.04, Debian 10, Debian 11, Debian 12, CentOS 8, Red Hat Universal Base Image (UBI) 8 and Red Hat Universal Base Image (UBI) 8 minimal.
Default value is
auto
which means GSC automatically detects the distro of the supplied Docker image. Users also have the option to provide one of the supported distros mentioned above.Warning
Please register and subscribe your host RHEL system to the Red Hat Customer Portal to use Red Hat Universal Base Image (UBI) 8 and UBI8-minimal distros.
-
Registry
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.
-
Gramine.Repository
Source repository of Gramine. Default value: https://github.com/gramineproject/gramine.git.
-
Gramine.Branch
Use this release/branch of the repository. Default value:
v1.6
.
-
Gramine.Image
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.
-
SGXDriver.Repository
Source repository of the Intel SGX driver. Default value: “” (in-kernel driver).
-
SGXDriver.Branch
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.
Warning
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>]
-
OPTIONS
¶
docker run options. Common options include
-it
(interactive with terminal),-d
(detached),--device
(forward device). Please see Docker manual for details.
-
IMAGE-NAME
¶
Name of original image (without GSC build).
-
ARGUMENTS
¶
Arguments to be supplied to the executable launching inside the Docker container and Gramine. Such arguments may only be provided when
--insecure-args
was specified during gsc build.
Execute with Linux PAL (gramine-direct)¶
You may select the Linux PAL (gramine-direct) at Docker run time
instead of the Linux-SGX PAL (gramine-sgx) 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.
-
GSC_PAL
¶ 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¶
Warning
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 (we pin to the Debian Bullseye version):
docker pull python:bullseye
Graminize the Python image using gsc build:
./gsc build --insecure-args python:bullseye test/generic.manifest
Sign the graminized Docker image using gsc sign-image:
./gsc sign-image python:bullseye enclave-key.pem
Retrieve SGX-related information from graminized image using gsc info-image:
./gsc info-image gsc-python:bullseye
Test the graminized Docker image (change
--device=/dev/sgx_enclave
to 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:bullseye -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:bullseye
Limitations¶
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, CentOS and Red Hat Universal Base
Image are supported by GSC. GSC can simply be extended to support other
distributions by providing a set of templates for this distribution in
templates/
.
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.
Workaround¶
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 /boot
, /dev
, .dockerenv
, .dockerinit
, /etc/mtab
,
/etc/rc
, /proc
, /sys
, and /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" ]
Issues with hostname and DNS¶
If your application queries the hostname or DNS information, you must manually add the following option to the manifest:
sys.enable_extra_runtime_domain_names_conf = true
For more information on this option, refer to https://gramine.readthedocs.io/en/stable/manifest-syntax.html#domain-names-configuration.