Google Engineers Are Becoming Concerned Over Some Arm Platforms Lacking Spectre V2 Mitigations

As a result of at least "a few AArch64 platforms" lacking firmware support for mitigating Spectre Variant Two, Google engineers are evaluating the possibility of Retpolines for the 64-bit Arm architecture.

Google's Anthony Steinhauser raised concerns that with these 64-bit Arm systems lacking their firmware support for mitigating Spectre V2, they could be compromised. Steinhauser noted, "In particular, on those systems, we believe the speculated targets of indirect branches in kernel code could potentially be controlled by userspace code."

So as part of Google's Safeside initiative for understanding and protecting against CPU side-channel issues, they are considering working on Retpolines (return trampolines) for AArch64. The possible implementation could make use of return stack predictors on AArch64 for handling. In doing so, they could fend off more Spectre V2 vulnerabilities even in cases where SoC vendors are not releasing firmware-based mitigations.

Google's Safeside folks are currently seeking feedback/interest in such an implementation, initially via the LLVM compiler community.