[Xen-devel] [PATCH RFC v12 09/21] pvh: Do not allow PVH guests to change paging modes

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
CC: Jan Beulich <jan.beulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 6a7a006..b59ff52 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1743,7 +1743,17 @@ int hvm_set_cr0(unsigned long value)
          (value & (X86_CR0_PE | X86_CR0_PG)) == X86_CR0_PG )
         goto gpf;
 
-    if ( (value & X86_CR0_PG) && !(old_value & X86_CR0_PG) )
+    
+
+    /* 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;
+    }
+    else if ( (value & X86_CR0_PG) && !(old_value & X86_CR0_PG) )
     {
         if ( v->arch.hvm_vcpu.guest_efer & EFER_LME )
         {
-- 
1.7.9.5


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