Preventing Your Faults From Telling Your Secrets: Defenses Against Pigeonhole Attacks
This addresses a critical security problem for users of hardware-secured systems by mitigating side-channel leaks, though it is incremental as it builds on existing defense concepts.
The paper tackles the vulnerability of enclaved execution systems like Intel SGX to page fault side-channel attacks, showing that these attacks can extract up to 100% of secret bits from cryptographic implementations, and proposes a software-only defense that reduces overhead to at most 29.22% with optimizations.
New hardware primitives such as Intel SGX secure a user-level process in presence of an untrusted or compromised OS. Such "enclaved execution" systems are vulnerable to several side-channels, one of which is the page fault channel. In this paper, we show that the page fault side-channel has sufficient channel capacity to extract bits of encryption keys from commodity implementations of cryptographic routines in OpenSSL and Libgcrypt --- leaking 27% on average and up to 100% of the secret bits in many case-studies. To mitigate this, we propose a software-only defense that masks page fault patterns by determinising the program's memory access behavior. We show that such a technique can be built into a compiler, and implement it for a subset of C which is sufficient to handle the cryptographic routines we study. This defense when implemented generically can have significant overhead of up to 4000X, but with help of developer-assisted compiler optimizations, the overhead reduces to at most 29.22% in our case studies. Finally, we discuss scope for hardware-assisted defenses, and show one solution that can reduce overheads to 6.77% with support from hardware changes.