Meltdown strikes back: the L1 terminal fault vulnerability [LWN.net]

Meltdown strikes back: the L1 terminal fault vulnerability

Posted Aug 14, 2018 22:35 UTC (Tue) by nilsmeyer (guest, #122604)
In reply to: Meltdown strikes back: the L1 terminal fault vulnerability by Sesse
Parent article: Meltdown strikes back: the L1 terminal fault vulnerability

You will also need to take care that nothing outside the VM is scheduled there (kernel threads, interrupts etc.).

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Meltdown strikes back: the L1 terminal fault vulnerability

Posted Aug 14, 2018 22:37 UTC (Tue) by Sesse (subscriber, #53779) [Link] (2 responses)

Yes—one would think this would be a good feature for a scheduler to have in general. (Think side-channel attacks in general.)

OpenBSD “solves” this by simply not supporting hyperthreading, but that seems too heavy-handed to me.

Meltdown strikes back: the L1 terminal fault vulnerability

Posted Aug 15, 2018 18:32 UTC (Wed) by jcm (subscriber, #18262) [Link] (1 responses)

It would be nice if we could guarantee no secrets were loaded, track, and flush them, but this isn't something most general purpose OS stacks running a full environment on a host do today. It is something some hypervisors are doing to mitigate against L1TF, and obviously is going to be investigated over time to improve the state of available mitigations on Linux, but it's very non-trivial.

Meltdown strikes back: the L1 terminal fault vulnerability

Posted Aug 15, 2018 18:34 UTC (Wed) by Sesse (subscriber, #53779) [Link]

FWIW, my request was for just “not at the same time” (to make timing attacks much harder), not flushing L1 on every context switch. That's too heavy-handed for most userspace.