SGX-LEGO: Fine-grained SGX controlled-channel attack and its countermeasure.

The introduction of Intel Software Guard eXtension (SGX) prompted security researchers to verify its effectiveness. One of the frequently discussed attacks against SGX is the side-channel attack by gathering page-fault information (controlled-channel attack). Owing to SGX’s hardware features, the faulting address of the enclave memory is page-masked. Because of this, both the controlled-channel attack and the defenses of SGX are built under the assumption that an attacker observes the memory access attempts of the enclave code with page-granularity. However, Van Bluck et al. recently demonstrated a controlled-channel attack technique which negates the prior assumption of page-granularity. In this paper, we introduce a new class of attack that stems from the reduced controlled-channel granularity, i.e., the Version IDentification attack (VID). The goal of VID attack is identifying the detailed code information inside SGX enclave by analyzing the fine-grained SGX controlled-channel. To protect enclave memory from such attack, we design and implement SGX-LEGO, an automated system that adopts execution polymorphism to the SGX enclave code. Previous defense approaches against controlled-channel attacks can be broadly categorized into two types: (i) disclosing the fault information and (ii) rendering the fault information useless. SGX-LEGO uses the latter approach by permuting the memory access sequence at the instruction level. In SGX-LEGO design, we leverage the concept of code-reuse-programming to overcome the implementation challenges regarding SGX page management. In the evaluation, we show how VID attacks the cryptographic functions, and demonstrate the efficacy of SGX-LEGO in security perspective and performance.