> > On Sun, 2018-01-28 at 12:40 -0800, Andy Lutomirski wrote: > > > > Do you mean that the host would intercept the guest WRMSR and do > > WRMSR itself? I would suggest that doing so is inconsistent with the > > docs. As specified, doing WRMSR to write 1 to IBRS does *not* > > protect the guest. > > I believe it does. Guest kernel is protected from any guest userspace > predictions learned before IBRS was last set to 1 in *any* mode, > including host.
the specification requires you to write a 1 on each transition to higher privilege. > > > For that matter, what are the semantics of VMRESUME doing a write to > > IBRS as part of its MSR switch? Is it treated as IBRS=1 from guest > > context? the guest ring 3 wouldn't have had time to do anything evil in the mean time so the vmresume write is valid. (anything else would be unworkable)
