Similar to the earlier Spectre and Meltdown bugs the new security flaw could allow access to sensitive data through a side channel. Intel says it’s not as serious as the chip flaws discovered in January, however, and ranked Lazy FPU as a “moderate” vulnerability.
The flaw can be exploited when the operating system uses “lazy” rather than “eager” floating point unit (FPU) switching instructions. A lazy restore means the FPU state is only saved when needed, as opposed to an eager restore, which happens on a scheduled basis.
As Red Hat explains in a blog about the chip flaw, developers may use a lazy restore to improve performance. But this also leaves the microprocessor vulnerable to a side-channel attack. “A newly scheduled task can use the exploit described herein to infer the floating point register state of another task, which can be used to leak sensitive information,” according to Red Hat.
Because of this, Intel says it “recommends system software developers utilize Eager FP state restore in lieu of Lazy FP state restore.” The chipmaker said many operating systems and hypervisor software have already address the problem, and it’s working with partners to patch the flaw.
“This issue, known as Lazy FP state restore, is similar to Variant 3a,” an Intel spokesperson wrote in an email to SDxCentral. “It has already been addressed for many years by operating system and hypervisor software used in many client and data center products. Our industry partners are working on software updates to address this issue for the remaining impacted environments and we expect these updates to be available in the coming weeks.”
Spectre is officially known as Variant 3a and Meltdown as Variant 4.
An AMD spokesperson said the company’s chips are not vulnerable: “Based on our analysis to date, we do not believe our products are susceptible to the recent security vulnerability identified around lazy FPU switching.”