Intel Warns of Lazy Restore Speculative Execution CPU Risk

Yet another speculative execution issue has been disclosed that potentially puts some Intel CPU users at risk.

processor flaw

This continues to be a challenging year for Intel from a security perspective. Having already had to deal with multiple security issues in 2018, the CPU giant publicly disclosed on June 13 a new security vulnerability that impacts some of its processors.

The flaw is known as a "Lazy FP (Floating Point) state restore" issue and is related in nature to the Meltdown and Spectre speculative execution vulnerabilities that were disclosed on Jan. 3.

"System software may utilize the Lazy FP state restore technique to delay the restoring of state until an instruction operating on that state is actually executed by the new process," Intel warned in its advisory. "Systems using Intel Core-based microprocessors may potentially allow a local process to infer data utilizing Lazy FP state restore from another process through a speculative execution side channel."

The Lazy FP issues add to multiple speculative execution issues disclosed in 2018. The initial Meltdown and Spectre disclosure on Jan. 3 identified three variants of potential side-channel attacks. On May 21, an additional two variants of Spectre and Meltdown were disclosed. The risk from the speculative execution issues is that an attacker could gain unauthorized access to system memory.

The Lazy restore vulnerability has been given the CVE-2018-3665 identifier, and Intel has rated it as having only moderate severity. The flaw was jointly reported to Intel by Julian Stecklina from Amazon Germany, Thomas Prescher from Cyberus Technology GmbH, Zdenek Sojka from SYSGO AG and security researcher Colin Percival.

"This vulnerability is similar to Meltdown (CVE-2017-5754)," Cyberus Technology wrote in a blog post. "While Meltdown allowed to read protected memory contents from a user space program, this new attack allows to read certain register contents across protection domain boundaries."

From a virtualization context, the Lazy restore issue can potentially impact virtual machine deployments, including the open-source Xen hypervisor. In a security advisory, the Xen project warned that an attacker could read CPU memory register state belonging to another virtual CPU (vCPU) previously scheduled on the same processor.  

"This can be state belonging a different guest, or state belonging to a different thread inside the same guest," the Xen advisory stated.

The Xen project has already released patches to deal with the issue. Among the largest users of Xen is Amazon Web Services, which uses Xen to help enable EC2 virtual machines on its public cloud.

"This issue does not impact AWS infrastructure," AWS stated in an advisory. "No customer's instance can read the memory or state of another customer’s instance, nor can any instance read AWS hypervisor memory or state."

AWS added that as a general security best practice, the cloud giant recommends that customers patch their operating systems or software as relevant patches become available to address speculative execution side-channel issues.


The impact of CVE-2018-3665 is currently limited to only Intel Core-based processors. In its advisory, Intel recommends that developers use an alternative floating point restore method known as Eager FP instead of Lazy FP.

Microsoft's advisory on the CVE-2018-3665 vulnerability does not list any specific patches as currently being available for the issue. Red Hat noted in its advisory that users of Red Hat Enterprise Linux (RHEL) 7 already benefit from the Eager FP approach on Sandy Bridge and newer Intel processors.

"RHEL 6 and earlier are impacted by this CVE and do not provide the eagerfpu parameter," Red Hat states. "Red Hat will be releasing updates which will change the behavior."

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.