Made public minutes ago is Transient Scheduler Attacks (TSA) as a new class of class of speculative side channel attacks affecting AMD processors.
The Linux kernel mitigation for Transient Scheduler Attacks was just merged to Linux Git:
“Add the mitigation logic for Transient Scheduler Attacks (TSA)
TSA are new aspeculative side channel attacks related to the execution timing of instructions under specific microarchitectural conditions. In some cases, an attacker may be able to use this timing information to infer data from other contexts, resulting in information leakage.
Add the usual controls of the mitigation and integrate it into the existing speculation bugs infrastructure in the kernel”
The new “MITIGATION_TSA” Kconfig option for Transient Scheduler Attacks mitigations adds:
“Enable mitigation for Transient Scheduler Attacks. TSA is a hardware security vulnerability on AMD CPUs which can lead to forwarding of invalid info to subsequent instructions and thus can affect their timing and thereby cause a leakage.”
The Linux kernel is also adding a new “tsa=” tunable for adjusting the TSA mitigation behavior on AMD CPUs to enable/disable or only mitigating user/kernel transitions or guest/host transitions for VMs.
Plus new AMD CPU microcode as part of the TSA disclosure was pushed to linux-firmware.git. That updated CPU microcode is just for Family 19h, so it’s not clear if only Family 19h CPUs are just affected or those are the only ones needing new microcode.
From quickly going through the TSA mitigation code for the Linux kernel, it would appear only Zen 3 and Zen 4 processors are affected. The AMD security bulletin for Transient Scheduler Attacks has yet to be made public on the AMD site and I haven’t seen any new website dedicated to the Transient Scheduler Attacks but presumably will be going public any minute now… That information should be much more insightful as well as confirming what generations of AMD processors are indeed impacted by TSA. I’ll work on some benchmarks of the Transient Scheduler Attacks mitigation impact on AMD CPUs soon.
