Ampere Altra before SRP 1.08b and Altra Max before SRP 2.05

Impact

Unprivileged readers get fine-grained CPU power telemetry, which is a data-dependent side channel: power correlates with the operands being processed, so it leaks key material and other secrets from workloads sharing the socket. On a multi-tenant Arm node this is a cross-tenant leak that needs no memory access at all - just a file read in sysfs. It is also a nuisance for anyone selling confidential inference, because the power trace of a model serving run is itself informative about the workload.

Who can reach it

Any unprivileged local user or container on an Altra / Altra Max host with the HWmon power sensors exposed. Containers that inherit the host sysfs make this trivially available to tenants.

What to do

Update to Altra SRP 1.08b / Altra Max SRP 2.05 or later, which restricts the telemetry. Flash + reboot + drain. Cheaper interim control that works today: restrict access to the HWmon power sensors (root-only permissions, do not bind-mount host /sys into tenant containers, drop the sensor nodes from the container's device allowlist). Losing per-core power telemetry costs you some capacity-planning visibility - decide whether your scheduler actually consumes it before turning it off fleet-wide.

References