On 12.01.2024 00:13, Andrew Cooper wrote:
> Right now, vvmx will blindly copy L12's ACTIVITY_STATE into the L02 VMCS and
> enter the vCPU. Luckily for us, nested-virt is explicitly unsupported for
> security bugs.
>
> The inactivity states are HLT, SHUTDOWN and WAIT-FOR-SIPI, and as noted by the
> SDM in Vol3 27.7 "Special Features of VM Entry":
>
> If VM entry ends with the logical processor in an inactive activity state,
> the VM entry generates any special bus cycle that is normally generated when
> that activity state is entered from the active state.
>
> Also,
>
> Some activity states unconditionally block certain events.
>
> I.e. A VMEntry with ACTIVITY=SHUTDOWN will initiate a platform reset, while a
> VMEntry with ACTIVITY=WAIT-FOR-SIPI will really block everything other than
> SIPIs.
>
> Both of these activity states are for the TXT ACM to use, not for regular
> hypervisors, and Xen doesn't support dropping the HLT intercept either.
>
> There are two paths in Xen which operate on ACTIVITY_STATE.
>
> 1) The vmx_{get,set}_nonreg_state() helpers for VM-Fork.
>
> As regular VMs can't use any inactivity states, this is just duplicating
> the 0 from construct_vmcs(). Retain the ability to query activity_state,
> but crash the domain on any attempt to set an inactivity state.
>
> 2) Nested virt, because of ACTIVITY_STATE in vmcs_gstate_field[].
>
> Explicitly hide the inactivity states in the guest's view of MSR_VMX_MISC,
> and remove ACTIVITY_STATE from vmcs_gstate_field[].
>
> In virtual_vmentry(), we should trigger a VMEntry failure for the use of
> any inactivity states, but there's no support for that in the code at all
> so leave a TODO for when we finally start working on nested-virt in
> earnest.
>
> Reported-by: Reima Ishii <[email protected]>
> Signed-off-by: Andrew Cooper <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>
with one remark/suggestion:
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1551,7 +1551,10 @@ static void cf_check vmx_set_nonreg_state(struct vcpu
> *v,
> {
> vmx_vmcs_enter(v);
>
> - __vmwrite(GUEST_ACTIVITY_STATE, nrs->vmx.activity_state);
> + if ( nrs->vmx.activity_state )
> + domain_crash(v->domain, "Attempt to set activity_state %#lx\n",
> + nrs->vmx.activity_state);
Might be useful to log the offending vCPU here?
Jan
