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Research artifact rated 'Reusable' for the paper "Faulty Point Unit: ABI Poisoning Attacks on Intel SGX" whiche appeared at ACSAC'20 and received an distinguished paper with artifacts award..

fritzalder/faulty-point-unit

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Faulty Point Unit: ABI Poisoning Attacks on Intel SGX

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This repository collects source code and data to reproduce the research published in our paper "Faulty Point Unit: ABI Poisoning Attacks on Intel SGX" to appear at ACSAC'20.

Abstract

This paper analyzes a previously overlooked attack surface that allows unprivileged adversaries to impact supposedly secure floating-point computations in Intel SGX enclaves through the Application Binary Interface (ABI). In a comprehensive study across 7 widely used industry-standard and research enclave shielding runtimes, we show that control and state registers of the x87 Floating-Point Unit(FPU) and Intel Streaming SIMD Extensions (SSE) are not always properly sanitized on enclave entry. First, we abuse the adversary's control over precision and rounding modes as a novel "ABI-level fault injection" primitive to silently corrupt enclaved floating-point operations, enabling a new class of stealthy, integrity-only attacks that disturb the result of SGX enclave computations. Our analysis reveals that this threat is especially relevant for applications that use the older x87 FPU, which is still being used under certain conditions for high-precision operations by modern compilers like gcc. We exemplify the potential impact of ABI-level quality-degradation attacks in a case study of an enclaved machine learning service and in a larger analysis on the SPEC benchmark programs. Second,we explore the impact on enclave confidentiality by showing that the adversary's control over floating-point exception masks can be abused as an innovative controlled channel to detect FPU usage and to recover enclaved multiplication operands in certain scenarios. Our findings, affecting 5 out of the 7 studied runtimes, demonstrate the fallacy and challenges of implementing high-assurance trusted execution environments on contemporary x86 hardware. We responsibly disclosed our findings to the vendors and were assigned two CVEs, leading to patches in the Intel SGX-SDK, Microsoft OpenEnclave, and the Rust compiler's SGX target.

@inproceedings{alder2020faulty,
    title     = {Faulty Point Unit: {ABI} Poisoning Attacks on {Intel SGX}},
    author    = {Alder, Fritz and Van Bulck, Jo and Oswald, David and Piessens, Frank},
    booktitle = {36th Annual Computer Security Applications Conference {(ACSAC)}},
    month     = Dec,
    year      = 2020,
}

Artifact description

In this artifact, we provide the means to reproduce all of our experimental results. More specifically, the repository is organized following the tables and figures in the paper. The following table overviews the different artifacts and further details which of them can be reproduced in SGX simulation mode in the Docker container we further describe below. A full reproducible build and reference output for all of the attacks that can be ran in the Docker SGX simulator can be viewed in the GitHub actions log.

Paper reference Directory Reproducible in Docker (simulation mode) Reproducible on SGX hardware Description
Table 1 01_table1_ basic-poc Yes Yes Proof-of-concept poisoning attack executed against an Intel SGX-SDK enclave. We provide the documented source code, build instructions, and the raw paper data.
Table 2 02_table2_ affected_runtimes Partially (full simulation: LKL, OE, Go-TEE; build-only: Rust-EDP) Yes List of affected enclave shielding runtimes. We provide proof-of-concept poisoning attacks against all runtimes marked with a star. Namely, OpenEnclave, SGX-LKL, Rust-EDP, and Go-TEE (for Intel SGX-SDK, see the artifact for Table 1).
Figure 4 03_section- 4_controlled-channel Yes Yes Controlled channel attack. We provide the documented proof-of-concept attacker and victim source code, build instructions, and the raw paper data.
Table 3 04_section- 5_mnist-javascript Yes Yes Machine learning with Javascript inside an enclave. We provide the documented source code, build instructions, and the raw paper data. This example was built on the open-source code of the S-FaaS project.
Table 4 05_section- 6_spec-cpu-2017 Limited, only with license. See notes on SPEC licensing* N/A Benchmarks with SPEC CPU 2017. Due to licensing and copyright restrictions with the proprietary SPEC 2017 suite, we can only provide the used configuration files and detailed instructions how to reproduce our results for people who already bought the SPEC CPU 2017 suite. Please note however, that obtaining the raw data for the SPEC benchmarks summarized in Table 4 takes several CPU weeks. We provide the log outputs of the full SPEC runs with detailed instructions of how to reproduce the summary in Table 4.
Figure 6 06_figure- 6_blender-outputs Same as Table 4* N/A Screenshot of the Blender benchmark. We provide the full reference output of Blender in normal conditions and under the attack.

*Note (on SPEC licensing). Due to licensing and copyright restrictions with the proprietary SPEC CPU 2017 suite, we can only provide the used configuration files and detailed instructions how to reproduce our results for people who already bought the SPEC CPU 2017 suite. Please note, however, that obtaining the raw data for the SPEC benchmarks summarized in Table 4 takes several CPU weeks. We provide the log outputs of the full SPEC runs with detailed instructions of how to reproduce the summary in Table 4.

Note (runtime). The table below lists a rough time estimate for the runtime of each artifact for the reviewer's convenience.

Paper reference Time required
Table 1 Immediate
Table 2 Once built, each runtime attack should execute in less than one minute.
Figure 4 Around 90 minutes for a full run.
Table 3 Around 10 minutes for a full run (using 8 threads).
Table 4 Reported log outputs provided. Producing these results will take multiple CPU weeks.
Figure 6 Reported images provided, see also notes of Table 4.

Preparation and setup

Detailed instructions to reproduce the above artifacts are provided in the READMEs of the respective subdirectories. In this section, we first overview the general setup common to all the experiments.

Building the Intel SGX simulator

All of the attacks described in our paper were performed on real SGX hardware. For the convenience of the artifact evaluation however, we ensured that all of our main results can also be ran in the official Intel SGX simulator, i.e., on normal processors without Intel SGX support. To easily run the simulator, we further provide an installation script and a Docker container with all the dependencies preinstalled.

Note (simulation validity). Simulation mode does assuredly not affect the validity of our attacks, as we exploit software sanitization oversights that occur in code that is agnostic to whether the enclave executes on real hardware or in a simulator.

Note (hardware access). Almost all of the enclave shielding runtimes that we studied offer a simulation mode (i.e., Intel SGX-SDK, OpenEnclave, LKL, GoTEE). Rust-EDP does not, however, and we can therefore not offer a simulation mode for our proof-of-concept attacks on the Rust-EDP runtime. This is only a concern for Table 2 (02_table2_affected_runtimes).

Quickstart: Pulling the latest Docker image

For a quickstart, you can pull the latest Docker image that is generated by the GitHub actions continuous integration. Do this by first installing Docker (loosely based on https://docs.docker.com/get-started/):

1. Install docker

$ sudo apt-get install docker.io

2. Configure user access

$ sudo usermod -aG docker $(whoami) # add users to docker group, then re-login.

3. Check your docker installation

$ docker run hello-world
[...]
This message shows that your installation appears to be working correctly.
[...]

4. Log in to GitHub to be able to retrieve the GitHub packages Docker container

Unfortunately, GitHub does permit to retrieve docker containers if one is not logged in to GitHub (as of early 2021). Thus, one first needs to authenticate to GitHub before being able to pull the docker image. The easiest way of doing this is to create a personal access token (specifically, the read:packages permission) and use docker login to authenticate to the GitHub services:

GITHUB_TOKEN=abc # Register your token here
GITHUB_USERNAME=abc # Your username
echo $GITHUB_AUTH_TOKEN | docker login docker.pkg.github.com -u $GITHUB_USERNAME --password-stdin

5. Quickstart with pulling the latest Docker image

We provide a Makefile target to easily pull the latest Docker image that has been built by the GitHub actions continuous integration. This pulls and creates a new interactive session in that Docker container to directly start with the artifact. Once inside the Docker container, you will still need to run the installation script and source the desired SDK (detailed below). A quick start with the Docker container looks as follows:

# Pull latest Docker build and start an interactive session inside the Docker container
$ make pull                                                                     24.8s  Tue 02 Mar 2021 03:22:20 PM UTC
docker pull docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu:latest
latest: Pulling from fritzalder/faulty-point-unit/sgx-fpu
Digest: sha256:fe6b074dbe1b811960cdaf5c90b73361dd3ceb8d919550e863db998a7932e6b8
Status: Image is up to date for docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu:latest
docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu:latest
docker run -i -h "badf1oa7" -t docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu
========================================================================
= Faulty Point Unit SGX simulator Docker container                     =
========================================================================
Description:	Ubuntu 18.04.5 LTS

To get started, see README.md in the current directory

root@badf1oa7$ ./sdk_helper.sh install_sim       # Install dependencies
...
root@badf1oa7$ source ./sdk_helper.sh vulnerable # Switch to the vulnerable Intel SGX SDK v2.7.1
root@badf1oa7$ cd 01_table1_basic-poc            
root@badf1oa7$ ./eval_simulator.sh               # Reproduce basic proof of concept attack
root@badf1oa7$ source ../sdk_helper.sh patched   # Now reproduce same attack with patched SDK v2.8.0
root@badf1oa7$ ./eval_simulator.sh

Switching Intel SGX-SDK versions

This artifact demonstrates an attack that existed in the Intel SGX-SDK in version 2.7.1 and was patched following with version 2.8.0. As such, we provide an easy to use install script that allows to reproduce the attack in both versions and be able to verify its mitigation in the patched SDK version.

We provide the script sdk_helper.sh to install and switch between the two relevant Intel SGX-SDK versions. Simply run ./sdk_helper.sh install to install the relevant dependencies in hardware mode or ./sdk_helper install_sim to install the dependencies in simulation mode if you have no intention of running the attack on real hardware. As described earlier, since this attack exploits software sanitization oversights, the simulation yields the same results when reproducing the data as real hardware will.

The sdk_helper.sh script has two options to switch between Intel SGX-SDK versions: sdk_helper.sh vulnerable and sdk_helper.sh patched to switch to the Intel SGX-SDK 2.7.1 and 2.8 respectively. Note that in order for the script to perform this switch reliably, this script needs to be called with source so that the environment variables that are set are inherited by your shell. As such, always call the script as source sdk_helper.sh vulnerable and source sdk_helper.sh patched!

Use ./sdk_helper.sh help to print an overview of commands and tasks the script performs.

Intel SGX-SDK bug in Ubuntu 20.04LTS

As of release of this artifact, there is a known issue with the Intel SGX-SDK and Ubuntu LTS 20.04 as reported here, here, and here. This is an issue in the SGX driver and does, therefore, not affect the simulator described above. The below workaround is, hence, only needed when running the attack on real SGX hardware on Ubuntu 20.04.

Since we are deliberately installing an obsolete Intel SGX-SDK to make it vulnerable to a known attack, we can not rely on future releases to patch this issue. A quick workaround is to set mount -o remount,exec /dev to circumvent the new behavior of Ubuntu 20.04. The sdk_helper sets this before installing if it detects the mentioned Ubuntu version. We explicitly warn of possible side-effects. Additionally, since this setting resets on reboot, a user might have to simply rerun the installation with the sdk_helper after a reboot.

Building your own Docker container

Optionally, to build a new Docker container instead of the automatically built one, use these commands:

$ make build
$ make run 
docker run -i -h "badf1oa7" -t docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu
========================================================================
= Faulty Point Unit SGX simulator Docker container                     =
========================================================================
Description:	Ubuntu 18.04.4 LTS

To get started, see README.md in the current directory

root@badf1oa7:/faulty-point-unit#

Running on real hardware

If you want to reproduce above artifacts on real hardware instead of using the SGX simulators, you can follow these instructions.

Ubuntu, RHEL, SUSE

We provide the sdk_helper.sh script that can be instructed to do a installation of the hardware driver via sudo ./sdk_helper.sh install. One installed, the sdk_helper.sh script can be used to switch between patched and vulnerable SDK: ./sdk_helper.sh vulnerable | ./sdk_helper.sh patched.

If needed, general installation instructions are provided by Intel here.

Potentially you also still have to start the aesmd service by running:

$ sudo service aesmd start

Arch Linux, Manjaro

The driver can be installed from the AUR here.

A docker image with the Intel SGX PSW installed can be obtained in the following way.

$ wget https://raw.githubusercontent.com/intel/linux-sgx/sgx_2.11/linux/installer/docker/Dockerfile
$ docker build --target aesm --build-arg https_proxy=$https_proxy \
             --build-arg http_proxy=$http_proxy -t sgx_aesm -f ./Dockerfile ./
$ rm Dockerfile
$ docker volume create --driver local --opt type=tmpfs --opt device=tmpfs --opt o=rw aesmd-socket

At the time of writing the AUR still contains the Legacy Launch Control driver and you can create the container with the following command

$ docker run --env http_proxy --env https_proxy --device=/dev/isgx -v /dev/log:/dev/log -v aesmd-socket:/var/run/aesmd -it sgx_aesm

If however the SGX Flexible Launch Control driver is installed on your system or the upcoming patches to the driver have been upstreamed you will need to create the container as follows

$ docker run --env http_proxy --env https_proxy --device=/dev/sgx/enclave --device=/dev/sgx/provision -v /dev/log:/dev/log -v aesmd-socket:/var/run/aesmd -it sgx_aesm

Running the container in Arch Linux for this repository

To start the docker container that has been built by the GitHub actions CI you can run the following.

$ docker pull docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu:latest

For the SGX Legacy Launch Control driver:

$ docker run -h "badf1oa7" --device=/dev/isgx -v aesmd-socket:/var/run/aesmd -it docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu

For the SGX Flexible Launch Control driver:

$ docker run -h "badf1oa7" --device=/dev/sgx/enclave -v aesmd-socket:/var/run/aesmd -it docker.pkg.github.com/fritzalder/faulty-point-unit/sgx-fpu

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Research artifact rated 'Reusable' for the paper "Faulty Point Unit: ABI Poisoning Attacks on Intel SGX" whiche appeared at ACSAC'20 and received an distinguished paper with artifacts award..

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