From 9001eb540b815110302505cfd799f1356f40e47f Mon Sep 17 00:00:00 2001
From: Mukesh Rathor <mukesh.rathor@oracle.com>
Date: Wed, 13 Nov 2013 09:35:58 +0100
Subject: [PATCH] pvh: do not allow PVH guests to change paging modes

Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Eddie Dong <eddie.dong@intel.com>
---
 xen/arch/x86/hvm/hvm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 484319f8eb..4df46bee09 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1818,6 +1818,15 @@ int hvm_set_cr0(unsigned long value)
          (value & (X86_CR0_PE | X86_CR0_PG)) == X86_CR0_PG )
         goto gpf;
 
+    /* A pvh is not expected to change to real mode. */
+    if ( is_pvh_vcpu(v)
+         && (value & (X86_CR0_PE | X86_CR0_PG)) != (X86_CR0_PG | X86_CR0_PE) )
+    {
+        printk(XENLOG_G_WARNING
+               "PVH attempting to turn off PE/PG. CR0:%lx\n", value);
+        goto gpf;
+    }
+
     if ( (value & X86_CR0_PG) && !(old_value & X86_CR0_PG) )
     {
         if ( v->arch.hvm_vcpu.guest_efer & EFER_LME )
-- 
2.30.2