On Fri, 15 Jun 2018, Juergen Gross wrote: > Like it is possible to switch off PTI in the kernel it is possible to do > the same with XPTI in the hypervisor (it is even possible to disable > XPTI for dom0 only). > > In case XPTI is disabled for the currently running system it is possible > to make use of Meltdown in user programs to read arbitrary physical host > memory (i.e. attacking the hypervisor) and this includes the own systems > kernel memory. > > So telling a user the system isn't vulnerable regarding Meltdown when > running as 64-bit pv-guest might not be the truth.
Ok, what a mess. As I don't think it'd be wise to try to let guest kernel figure out whether host has XPTI, I'd suggest at least making the message somehow more informative. Something like + if (hypervisor_is_type(X86_HYPER_XEN_PV)) + return sprintf(buf, "Unknown (XEN PV detected, hypervisor mitigation required\n"); perhaps? Thanks, -- Jiri Kosina SUSE Labs
