Spectre Returns! Speculation Attacks using the Return Stack Buffer

Abstract

The recent Spectre attacks exploit speculative execution, a pervasively used feature of modern microprocessors, to allow the exfiltration of sensitive data across protection boundaries. In this paper, we introduce a new Spectreclass attack that we call SpectreRSB. In particular, rather than exploiting the branch predictor unit, SpectreRSB exploits the return stack buffer (RSB), a common predictor structure in modern CPUs used to predict return addresses. We show that both local attacks (within the same process such as Spectre 1) and attacks on SGX are possible by constructing proof of concept attacks. We also analyze additional types of the attack on the kernel or across address spaces and show that under some practical and widely used conditions they are possible. Importantly, none of the known defenses including Retpoline and Intel's microcode patches stop all SpectreRSB attacks. We believe that future system developers should be aware of this vulnerability and consider it in developing defenses against speculation attacks. In particular, on Core-i7 Skylake and newer processors (but not on Intel's Xeon processor line), a patch called RSB refilling is used to address a vulnerability when the RSB underfills; this defense interferes with SpectreRSB's ability to launch attacks that switch into the kernel. We recommend that this patch should be used on all machines to protect against SpectreRSB.

A Survey of Published Attacks on Intel SGX

“…Koruyeh et al mentions in SpectreRSB paper [32] that the microcode patch "RSB-refilling" is not specifically applied for SGX enclaves. Based on this we draw the conclusion that RSB-refilling ought to be implemented either the SDKs or compilers, if they wish to ensure protection against the SpectreRSB.…”

“…The authors presented the SgxPectre attack and used it to extract the secret seal keys and attestation keys from Intel signed quoting enclaves. In [32] Koruyeh et al proposed the SpectreRSB attack which alternatively uses the return stack buffer which is a structure in modern CPUs used to speculatively predict the return address of execution frames (functions). SgxSpectre in [33] (not to be confused with SgxPectre [31]) also demonstrated a successful attack on SGX enclaves using a slight modification of the Spectre variant 1 attack.…”

STBPU: A Reasonably Secure Branch Prediction Unit

“…With a decreasing number of available targets for software attacks, the attention of adversaries is more frequently drawn to exploitable weaknesses in hardware. Although hardware attacks such as microarchitectural side channels [1], [3], [6], [19], [26], [44], [56], [57], covert channels [17], [24], [49], [54], and power analysis [2], [34], [48], [50], [55] attacks have been known for a long time, only recently did researchers demonstrate the true power of microarchitectural attacks with newly discovered speculative execution attacks, such as Meltdown [42], [73] and Spectre [13], [32], [33], [35], [47], [67]. These attacks are based on speculative (transient) execution, a performance optimization technique present in nearly all of today's processors.…”