On Wed, Jan 10, 2018 at 11:58:54AM +0000, David Woodhouse wrote: > On Wed, 2018-01-10 at 12:54 +0100, Andrea Arcangeli wrote: > > On Wed, Jan 10, 2018 at 09:27:59AM +0000, David Woodhouse wrote: > > > I don't know why you're calling that 'IBRS=2'; are you getting > > confused > > > by Andrea's distro horridness? > > > > Eh, yes he's got confused. ibrs_enabled 2 simply means to leave IBRS > > set in SPEC_CTLR 100% of the time, except in guest mode. > > On all current hardware, if you only set IBRS when you exit a guest, > then you are not protecting yourself from userspace at all. IBRS acts > as a *barrier* in all current hardware.
Kernel memory is 100% protected if you set only IBRS at vmexit. Once IBRS is set, there's no way any userland (nor host nor guest) can attack the kernel memory through spectre variant#2. What is not protected is host userland from guest userland which is point 3 in the email I posted earlier and I already provided all details there on how to fix that purely theoretical issue not part of the PoC with the provided debugfs tunables, so I won't repeat here.
