Trusted execution environments, and particularly the Software Guard eXtensions (SGX) included in recent Intel x86 processors, gained significant traction in recent years. A long track of research papers, and increasingly also real-world industry applications, take advantage of the strong hardware-enforced confidentiality and integrity guarantees provided by Intel SGX. Ultimately, enclaved execution holds the compelling potential of securely offloading sensitive computations to untrusted remote platforms.

We present Foreshadow, a practical software-only microarchitectural attack that decisively dismantles the security objectives of current SGX implementations. Crucially, unlike previous SGX attacks, we do not make any assumptions on the victim enclave's code and do not necessarily require kernel-level access. At its core, Foreshadow abuses a speculative execution bug in modern Intel processors, on top of which we develop a novel exploitation methodology to reliably leak plaintext enclave secrets from the CPU cache. We demonstrate our attacks by extracting full cryptographic keys from Intel's vetted architectural enclaves, and validate their correctness by launching rogue production enclaves and forging arbitrary local and remote attestation responses. The extracted remote attestation keys affect millions of devices.

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Foreshadow: extracting the keys to the intel SGX kingdom with transient out-of-order execution

Intel SGX isolates the memory of security-critical applications from the untrusted OS. However, it has been speculated that SGX may be vulnerable to side-channel attacks through shared caches. We developed new cache attack techniques customized for SGX. Our attack differs from other SGX cache attacks in that it is easy to deploy and avoids known detection approaches. We demonstrate the effectiveness of our attack on two case studies: RSA decryption and genomic processing. While cache timing attacks against RSA and other cryptographic operations can be prevented by using appropriately hardened crypto libraries, the same cannot be easily done for other computations, such as genomic processing. Our second case study therefore shows that attacks on noncryptographic but privacy sensitive operations are a serious threat. We analyze countermeasures and show that none of the known defenses eliminates the attack.

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Software grand exposure: SGX cache attacks are practical

In modern computer systems, user processes are isolated from each other by the operating system and the hardware. Additionally, in a cloud scenario it is crucial that the hypervisor isolates tenants from other tenants that are co-located on the same physical machine. However, the hypervisor does not protect tenants against the cloud provider and thus the supplied operating system and hardware. Intel SGX provides a mechanism that addresses this scenario. It aims at protecting user-level software from attacks from other processes, the operating system, and even physical attackers.

Malware Guard Extension: Using SGX to Conceal Cache Attacks

Smart contracts are applications that execute on blockchains. Today they manage billions of dollars in value and motivate visionary plans for pervasive blockchain deployment. While smart contracts inherit the availability and other security assurances of blockchains, however, they are impeded by blockchains' lack of confidentiality and poor performance. 
We present Ekiden, a system that addresses these critical gaps by combining blockchains with Trusted Execution Environments (TEEs). Ekiden leverages a novel architecture that separates consensus from execution, enabling efficient TEE-backed confidentiality-preserving smart-contracts and high scalability. Our prototype (with Tendermint as the consensus layer) achieves example performance of 600x more throughput and 400x less latency at 1000x less cost than the Ethereum mainnet. 
Another contribution of this paper is that we systematically identify and treat the pitfalls arising from harmonizing TEEs and blockchains. Treated separately, both TEEs and blockchains provide powerful guarantees, but hybridized, though, they engender new attacks. For example, in naive designs, privacy in TEE-backed contracts can be jeopardized by forgery of blocks, a seemingly unrelated attack vector. We believe the insights learned from Ekiden will prove to be of broad importance in hybridized TEE-blockchain systems.

Ekiden: A Platform for Confidentiality-Preserving, Trustworthy, and Performant Smart Contract Execution

Side-channel risks of Intel SGX have recently attracted great attention Under the spotlight is the newly discovered page-fault attack, in which an OS-level adversary induces page faults to observe the page-level access patterns of a protected process running in an SGX enclave With almost all proposed defense focusing on this attack, little is known about whether such efforts indeed raise the bar for the adversary, whether a simple variation of the attack renders all protection ineffective, not to mention an in-depth understanding of other attack surfaces in the SGX system In the paper, we report the first step toward systematic analyses of side-channel threats that SGX faces, focusing on the risks associated with its memory management Our research identifies 8 potential attack vectors, ranging from TLB to DRAM modules More importantly, we highlight the common misunderstandings about SGX memory side channels, demonstrating that high frequent AEXs can be avoided when recovering EdDSA secret key through a new page channel and fine-grained monitoring of enclave programs (at the level of 64B) can be done through combining both cache and cross-enclave DRAM channels Our findings reveal the gap between the ongoing security research on SGX and its side-channel weaknesses, redefine the side-channel threat model for secure enclaves, and can provoke a discussion on when to use such a system and how to use it securely

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Leaky Cauldron on the Dark Land: Understanding Memory Side-Channel Hazards in SGX

For the first time, we practically demonstrate that Intel SGX enclaves are vulnerable against cache-timing attacks. As a case study, we present an access-driven cache-timing attack on AES when running inside an Intel SGX enclave. Using Neve and Seifert's elimination method, as well as a cache probing mechanism relying on Intel PMC, we are able to extract the AES secret key in less than 10 seconds by investigating 480 encrypted blocks on average. The AES implementation we attack is based on a Gladman AES implementation taken from an older version of OpenSSL, which is known to be vulnerable to cache-timing attacks. In contrast to previous works on cache-timing attacks, our attack is executed with root privileges running on the same host as the vulnerable enclave. Intel SGX, however, was designed to precisely protect applications against such root-level attacks. As a consequence, we show that SGX cannot withstand its designated attacker model when it comes to side-channel vulnerabilities. To the contrary, the attack surface for side-channels increases dramatically in the scenario of SGX due to the power of root-level attackers, for example, by exploiting the accuracy of PMC, which is restricted to kernel code.

Cache Attacks on Intel SGX

In spite of their effectiveness in the context of vulnerability discovery, current state-of-the-art binary program analysis approaches are limited by inherent trade-offs between accuracy and scalability. In this paper, we identify a set of vulnerability properties that can aid both static and dynamic vulnerability detection techniques, improving the precision of the former and the scalability of the latter. By carefully integrating static and dynamic techniques, we detect vulnerabilities that exhibit these properties in real-world programs at a large scale. We implemented our technique, making several advance-ments in the analysis of binary code, and created a prototype called A RBITER . We demonstrate the effectiveness of our approach with a large-scale evaluation on four common vulnerability classes: CWE-131 (Incorrect Calculation of Buffer Size), CWE-252 (Unchecked Return Value), CWE-134 (Un-controlled Format String), and CWE-337 (Predictable Seed in Pseudo-Random Number Generator). We evaluated our approach on more than 76,516 x86-64 binaries in the Ubuntu repositories and discovered new vulnerabilities, including a ﬂaw inserted into programs during compilation. data-ﬂow vulnerabilities, P2 refers to easily identiﬁable sources and sinks and P3 refers to control-ﬂow-determined aliasing. In this paper, we speciﬁcally explore the automatic detection CWE’s 131, 134, 252 and 337.

Moritz Eckert

Papers

Cache Attacks on Intel SGX

Arbiter: Bridging the Static and Dynamic Divide in Vulnerability Discovery on Binary Programs