[Xen-devel] vmx & efer

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

Am I blind in that I cannot find the place where the guest intended EFER value
gets loaded into the CPU register? The VMCS has no field for this (other than
AMD's VMCB), and the guest_msr_state->flags bit for this register doesn't get
set anywhere. I'm implying that the guest thus always runs with all features
enabled that were enabled by the hypervisor (slight security issue, as EFER.SCE
set implies LSTAR was initialized, which may not be true).

Further I am quite confused about the saving and restoring of CSTAR - all
parts of the SDM state or imply that this register doesn't exist (as syscall is
supposedly invalid in compatibility mode), so it wouldn't need saving/restoring
at all; there's one exception though: section 25.10.4.3 says "SYSCALL/SYSRET
invocations can occur from either 32-bit compatibility mode application code
or from 64-bit application code."

Thanks, Jan


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