KVM: VMX: Fix host GDT.LIMIT corruption

vmx does not restore GDT.LIMIT to the host value, instead it sets it to 64KB.
This means host userspace can learn a few bits of host memory.

Fix by reloading GDTR when we load other host state.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2fdcc9819f36..27a0222c2946 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -185,6 +185,7 @@ static void kvm_cpu_vmxoff(void);
 static DEFINE_PER_CPU(struct vmcs *, vmxarea);
 static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
 static DEFINE_PER_CPU(struct list_head, vcpus_on_cpu);
+static DEFINE_PER_CPU(struct desc_ptr, host_gdt);
 
 static unsigned long *vmx_io_bitmap_a;
 static unsigned long *vmx_io_bitmap_b;
@@ -871,6 +872,7 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
 #endif
         if (current_thread_info()->status & TS_USEDFPU)
                 clts();
+        load_gdt(&__get_cpu_var(host_gdt));
 }
 
 static void vmx_load_host_state(struct vcpu_vmx *vmx)
@@ -1379,6 +1381,8 @@ static int hardware_enable(void *garbage)
                 ept_sync_global();
         }
 
+        store_gdt(&__get_cpu_var(host_gdt));
+
         return 0;
 }