Linux perf/x86/amd/brs - kernel address leakage through Branch Sampling: MULTI-TENANT ISOLATION: A user-only branch

Impact

MULTI-TENANT ISOLATION: A user-only branch stack collected via AMD Branch Sampling can contain branches that originated in the kernel, so unprivileged profiling leaks kernel addresses. That is a KASLR break handed to any tenant allowed to profile their own code - and on AI clusters, letting tenants profile their own GPU and CPU kernels is a feature people ask for. Combine it with any of the amdgpu memory-safety bugs in this database and you have a reliable local privilege escalation.

Who can reach it

Local, from a process permitted to use perf branch sampling. How reachable this is depends entirely on your perf_event_paranoid setting - if you relaxed it so tenants can profile, you granted this.

What to do

Fixed in the Linux kernel by filtering kernel branches out of user-only branch stacks. Distro kernel update plus reboot; no firmware step. In the meantime, review perf_event_paranoid on GPU nodes: the value that makes tenant profiling work is the same value that exposes this.

References