VUSec security research group and Intel on Tuesday disclosed a yet another Spectre-class speculative execution vulnerability called branch history injection (BHI). The new exploit affects all of Intel processors released in the recent years, including the latest Alder Lake CPUs, and select Arm cores. By contrast, AMD's chips are believed to be unaffected.
BHI is a proof-of-concept attack that affects CPUs already vulnerable to Spectre V2 exploits, but with all kinds of mitigations already in place. The new exploit bypasses Intel's eIBRS and Arm's CSV2 mitigations, reports Phoronix. BHI re-enables cross-privilege Spectre-v2 exploits, allows kernel-to-kernel (so-called intra-mode BTI) exploits, and allows perpetrators to inject predictor entries into the global branch prediction history to make kernel leak data, reports VUSec. As a result, arbitrary kernel memory on select CPUs can be leaked and potentially reveal confidential information, including passwords. An example of how such a leak can happen was published here.
All of Intel's processors beginning with Haswell (launched in 2013) and extending to the latest Ice Lake-SP and Alder Lake are affected by the vulnerability, but Intel is about to release a software patch that will mitigate the issue.
Numerous cores from Arm, including Cortex A15, A57, A72 as well as Neoverse V1, N1, and N2 are also affected. Arm is expected to release software mitigations for its cores. What is unclear is whether custom versions of these cores (e.g., select cores from Qualcomm) are also affected and when the potential security holes will be covered.
Since this is a proof-of-concept vulnerability and it is being mitigated by Intel and Arm, it should not be able to be used to attack a client or server machine — as long as all the latest patches are installed. There's no indication how much the mitigations will impact performance.