x86/vmx: Disallow the use of inactivity states

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 <ishiir@g.ecc.u-tokyo.ac.jp>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tamas K Lengyel <tamas@tklengyel.com>

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 %pv activity_state %#lx\n",
+                     v, nrs->vmx.activity_state);
+
     __vmwrite(GUEST_INTERRUPTIBILITY_INFO, nrs->vmx.interruptibility_info);
     __vmwrite(GUEST_PENDING_DBG_EXCEPTIONS, nrs->vmx.pending_dbg);
 

xen/arch/x86/hvm/vmx/vvmx.c

@@ -899,7 +899,10 @@ static const u16 vmcs_gstate_field[] = {
     GUEST_LDTR_AR_BYTES,
     GUEST_TR_AR_BYTES,
     GUEST_INTERRUPTIBILITY_INFO,
+    /*
+     * ACTIVITY_STATE is handled specially.
     GUEST_ACTIVITY_STATE,
+     */
     GUEST_SYSENTER_CS,
     GUEST_PREEMPTION_TIMER,
     /* natural */
@@ -1200,6 +1203,8 @@ static void virtual_vmentry(struct cpu_user_regs *regs)
     nvcpu->nv_vmentry_pending = 0;
     nvcpu->nv_vmswitch_in_progress = 1;
 
+    /* TODO: Fail VMentry for GUEST_ACTIVITY_STATE != 0 */
+
     /*
      * EFER handling:
      * hvm_set_efer won't work if CR0.PG = 1, so we change the value
@@ -2316,8 +2321,8 @@ int nvmx_msr_read_intercept(unsigned int msr, u64 *msr_content)
         data = hvm_cr4_guest_valid_bits(d);
         break;
     case MSR_IA32_VMX_MISC:
-        /* Do not support CR3-target feature now */
-        data = host_data & ~VMX_MISC_CR3_TARGET;
+        /* Do not support CR3-targets or activity states. */
+        data = host_data & ~(VMX_MISC_CR3_TARGET | VMX_MISC_ACTIVITY_MASK);
         break;
     case MSR_IA32_VMX_EPT_VPID_CAP:
         data = nept_get_ept_vpid_cap();

xen/arch/x86/include/asm/hvm/vmx/vmcs.h

@@ -277,6 +277,7 @@ extern u32 vmx_secondary_exec_control;
 #define VMX_VPID_INVVPID_SINGLE_CONTEXT_RETAINING_GLOBAL 0x80000000000ULL
 extern u64 vmx_ept_vpid_cap;
 
+#define VMX_MISC_ACTIVITY_MASK                  0x000001c0
 #define VMX_MISC_PROC_TRACE                     0x00004000
 #define VMX_MISC_CR3_TARGET                     0x01ff0000
 #define VMX_MISC_VMWRITE_ALL                    0x20000000