Linux 7.3-rc7 Adds Kernel Workaround for AMD TLBI Erratum 1718

The Linux 7.3-rc7 kernel release, published today, includes a software workaround for AMD TLBI Erratum #1718. This addition provides a mitigation path for systems running affected AMD processors that have not yet received the necessary CPU microcode updates, according to reporting by Phoronix.

AMD TLBI Erratum #1718 involves a hardware defect in certain Zen-based CPUs. The issue arises when the Translation Lookaside Buffer Invalidate Instruction is used, potentially leading to stale translation entries. While AMD addressed this primarily through CPU microcode updates, the Linux kernel team has implemented a complementary software layer to handle cases where microcode is not current.

Context and Background

The primary mitigation for this hardware defect was delivered via CPU microcode updates from AMD. These updates address the root cause of the defect in the processor's handling of translation lookaside buffer invalidations. However, not all systems may have received or applied these microcode updates, leaving a gap in protection for some users until the kernel workaround is deployed.

According to Phoronix, the kernel workaround is being introduced in the 7.3-rc7 release. This release candidate is part of the development cycle for the upcoming stable 7.3 kernel. The inclusion of this workaround ensures that systems relying on older microcode can still operate with reduced risk of issues stemming from stale translation entries during instruction execution.

Who Is Affected

This issue affects users of certain AMD Zen CPUs. Specifically, systems that are running affected processors but are not running the updated AMD microcode are the primary candidates for this kernel mitigation. Users who have already applied the latest microcode updates may not need the kernel workaround, as the hardware-level fix takes precedence. However, the kernel change provides an additional safety net for those who cannot update microcode immediately.

The workaround is being back-ported to prior kernel versions. This means that users running older, stable kernels will also benefit from the mitigation once their distribution vendors integrate the back-ported changes. This broadens the scope of protection beyond just those on the latest kernel development releases.

What should you do?

System administrators should verify their current kernel version and check if it includes the workaround for Erratum #1718. Users on affected AMD Zen hardware should prioritize applying available microcode updates from AMD as the primary fix. For those unable to update microcode, upgrading to a kernel version that includes the back-ported workaround is recommended. Monitoring vendor announcements for stable kernel updates containing this mitigation is also advised.

What to do and how to stay safe: AMD

• Check if your system is running an affected AMD Zen CPU by reviewing processor specifications.
• Verify whether your current CPU microcode version includes the fix for TLBI Erratum #1718.
• Update to the latest available kernel version that includes the back-ported workaround if microcode cannot be updated.
• Monitor official vendor channels for updates on kernel back-ports to stable releases.

General security guidance from the Threat Times newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

What is AMD TLBI Erratum #1718?

It is a hardware defect in certain Zen CPUs where the Translation Lookaside Buffer Invalidate Instruction can lead to stale translation entries.

Does this fix require a new CPU?

No, the fix is provided through CPU microcode updates and a Linux kernel workaround, not hardware replacement.

Will older kernels get this fix?

Yes, the kernel workaround is being back-ported to prior kernel versions, according to Phoronix.