An information leakage flaw is found in the way Linux kernel saves and restores Floating Point Unit(FPU) state during task switch. There are two ways, one is to save & restore FPU state during task context switch. And second is to defer FPU state save & restore until an FP instruction is invoked by the current task. First is called as "Eager FPU Restore" and second is known as "Lazy FPU Restore" scheme.

Linux kernel which follows the "Lazy FPU Restore" scheme is vulnerable to the FPU state information leakage issue. An unprivileged local attacker could use this flaw to read FPU state bits by conducting targeted cache side-channel attacks, similar to Meltdown attack disclosed earlier this year.

Upstream fix: ------------- -> https://git.kernel.org/linus//58122bf1d856a4ea9581d62a07c557d997d46a19

References: ----------- -> http://www.openwall.com/lists/oss-security/2018/06/13/7