x86/hvm: Disallow the creation of HVM domains without Local APIC emulation

There are multiple problems, not necesserily limited to:

 * Guests which configure event channels via hvmop_set_evtchn_upcall_vector(),
   or which hit %cr8 emulation will cause Xen to fall over a NULL vlapic->regs
   pointer.

 * On Intel hardware, disabling the TPR_SHADOW execution control without
   reenabling CR8_{LOAD,STORE} interception means that the guests %cr8
   accesses interact with the real TPR.  Amongst other things, setting the
   real TPR to 0xf blocks even IPIs from interrupting this CPU.

 * On hardware which sets up the use of Interrupt Posting, including
   IOMMU-Posting, guests run without the appropriate non-root configuration,
   which at a minimum will result in dropped interrupts.

Whether no-LAPIC mode is of any use at all remains to be seen.

This is XSA-256.

Reported-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Gbp-Pq: Name x86hvm-disallow-the-creation-of-hvm-doma.patch

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 8817263ac5fe732bf55f15aa2d573075df0f9568..91b9ab75b49512c4ae7ff41bd69e9dc67b0c4edd 100644 (file)
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -557,11 +557,9 @@ int arch_domain_create(struct domain *d, unsigned int domcr_flags,
             return -EINVAL;
         }
 
-        /* PVHv2 guests can request emulated APIC. */
-        if ( emflags &&
-            (is_hvm_domain(d) ? ((emflags != XEN_X86_EMU_ALL) &&
-                                 (emflags != XEN_X86_EMU_LAPIC)) :
-                                (emflags != XEN_X86_EMU_PIT)) )
+        if ( is_hvm_domain(d) ? ((emflags != XEN_X86_EMU_ALL) &&
+                                 (emflags != XEN_X86_EMU_LAPIC))
+                              : (emflags && emflags != XEN_X86_EMU_PIT) )
         {
             printk(XENLOG_G_ERR "d%d: Xen does not allow %s domain creation "
                    "with the current selection of emulators: %#x\n",