Ampere Altra before 1.08g and Altra Max before 2.05a - return address prediction: An attacker can control

Impact

An attacker can control return-address predictions and steer speculative execution into a chosen gadget, then read the result out of the cache. Same practical outcome as Spectre-v2 on these parts: cross-privilege and, where cores are shared, cross-tenant reads of memory the attacker has no rights to. Relevant to anyone running Altra as a CPU head node in front of GPU workers, since that node typically holds cluster credentials and customer data in flight.

Who can reach it

Unprivileged local code on an affected Altra / Altra Max part, targeting a victim on the same core or the same branch predictor structures. Local only.

What to do

Update Altra firmware to 1.08g / Altra Max 2.05a or later from the board OEM, plus the corresponding kernel mitigations. Flash + reboot + drain. Speculation mitigations on Arm cost real throughput on syscall- and context-switch-heavy paths, so benchmark your actual serving stack rather than accepting the vendor's number. As with every predictor-sharing bug, not co-scheduling untrusted tenants on the same physical core is the mitigation that does not degrade over time.

References

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