* Woodhouse, David ([email protected]) wrote: > On Mon, 2018-01-08 at 02:42 -0800, Paul Turner wrote: > > > > While the cases above involve the crafting and use of poisoned > > entries. Recall also that one of the initial conditions was that we > > should avoid RSB underflow as some CPUs may try to use other indirect > > predictors when this occurs. > > I think we should start by deliberately ignoring the CPUs which use the > other indirect predictors on RSB underflow. Those CPUs don't perform > *quite* so badly with IBRS anyway. > > Let's get the minimum amount of RSB handling in to cope with the pre- > SKL CPUs, and then see if we really do want to extend it to make SKL > 100% secure in retpoline mode or not.
How do you make decisions on which CPU you're running on? I'm worried about the case of a VM that starts off on an older host and then gets live migrated to a new Skylake. For Intel CPUs we've historically been safe to live migrate to any newer host based on having all the features that the old one had; with the guest still seeing the flags etc for the old CPU. Dave -- Dr. David Alan Gilbert / [email protected] / Manchester, UK
