A Floating Point Unit (FPU) state information leakage flaw was found in the way the Linux kernel saved and restored the FPU state during task switch. Linux kernels that follow the "Lazy FPU Restore" scheme are 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 the Meltdown vulnerability disclosed earlier this year.
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This issue affects the versions of the Linux kernel as shipped with Red Hat Enterprise Linux 5, 6, 7, and Red Hat Enterprise MRG 2. Future kernel updates for Red Hat Enterprise Linux 5, 6, 7, and Red Hat Enterprise MRG 2 may address this issue.
RHEL-7 will automatically default to (safe) “eager” floating point register restore on Sandy Bridge and newer Intel processors. AMD processors are not affected. You can mitigate this issue on older processors by booting the kernel with the 'eagerfpu=on' parameter to enable eager FPU restore mode. In this mode FPU state is saved and restored for every task/context switch regardless of whether the current process invokes FPU instructions or not. The parameter does not affect performance negatively, and can be applied with no adverse effects to processors that are not affected.