Software Guard Extensions
Intel Software Guard Extensions (SGX) is a set of central processing unit (CPU) instruction codes from Intel that allows user-level code to allocate private regions of memory, called enclaves, that are protected from processes running at higher privilege levels. Intel designed SGX to be useful for implementing secure remote computation, secure web browsing, and digital rights management (DRM).
Support for SGX in the CPU is indicated in CPUID "Structured Extended feature Leaf", EBX bit 02, but its availability to applications requires BIOS support and opt-in enabling which is not reflected in CPUID bits. This complicates the feature detection logic for applications.
Emulation of SGX was added to an experimental version of the QEMU system emulator in 2014. In 2015, researchers at the Georgia Institute of Technology released an open-source simulator known as OpenSGX.
One example of SGX used in security was a demo application from wolfSSL using it for cryptography algorithms. One example of a secure service built using SGX is Fortanix's key management service. This entire cloud based service is built using SGX servers and designed to provide privacy from cloud providers. An additional example is Numecent using SGX to protect the DRM that is used to authorize application execution with their Cloudpaging application delivery products.
On 27 March 2017 researchers at Austria's Graz University of Technology developed a proof-of-concept that can grab RSA keys from SGX enclaves running on the same system within five minutes by using certain CPU instructions in lieu of a fine-grained timer to exploit cache DRAM side-channels. One countermeasure for this type of attack was presented and published by Daniel Gruss et al. at the USENIX Security Symposium in 2017. Among other published countermeasures, one countermeasure to this type of attack was published on September 28, 2017, a compiler-based tool, DR.SGX, that claims to have superior performance with the elimination of the implementation complexity of other proposed solutions.
The LSDS group at Imperial College London showed a proof of concept that the Spectre speculative execution security vulnerability can be adapted to attack the secure enclave. The Foreshadow attack, disclosed in August 2018, combines speculative execution and buffer overflow to bypass the SGX.
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- Schwarz, Michael; Weiser, Samuel; Gruss, Daniel; Maurice, Clémentine; Mangard, Stefan (March 1, 2017). "Malware Guard Extension: Using SGX to Conceal Cache Attacks". Graz University of Technology. arXiv: . Bibcode:2017arXiv170208719S.
- "Strong and Efficient Cache Side-Channel Protection using Hardware Transactional Memory" (PDF). USENIX. 2017-08-16.
- "DR.SGX: Hardening SGX Enclaves against Cache Attacks with Data Location Randomization" (PDF). 2017-09-28.
- Sample code demonstrating a Spectre-like attack against an Intel SGX enclave.
- Intel Software Guard Extensions (Intel SGX) / ISA Extensions, Intel
- Intel Software Guard Extensions (Intel SGX) Programming Reference, Intel, October 2014
- IDF 2015 - Tech Chat: A Primer on Intel Software Guard Extensions, Intel (poster)
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- Victor Costan and Srinivas Devadas, Intel SGX Explained, January 2016.
- wolfSSL, October 2016.
- The Security of Intel SGX for Key Protection and Data Privacy Applications / Professor Yehuda Lindell (Bar Ilan University & Unbound Tech), January 2018