[PATCH 4.14 061/118] KVM: x86: Add memory barrier on vmcs field lookup

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Honig <aho...@google.com>

commit 75f139aaf896d6fdeec2e468ddfa4b2fe469bf40 upstream.

This adds a memory barrier when performing a lookup into
the vmcs_field_to_offset_table.  This is related to
CVE-2017-5753.

Signed-off-by: Andrew Honig <aho...@google.com>
Reviewed-by: Jim Mattson <jmatt...@google.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 arch/x86/kvm/vmx.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -888,8 +888,16 @@ static inline short vmcs_field_to_offset
 {
        BUILD_BUG_ON(ARRAY_SIZE(vmcs_field_to_offset_table) > SHRT_MAX);
 
-       if (field >= ARRAY_SIZE(vmcs_field_to_offset_table) ||
-           vmcs_field_to_offset_table[field] == 0)
+       if (field >= ARRAY_SIZE(vmcs_field_to_offset_table))
+               return -ENOENT;
+
+       /*
+        * FIXME: Mitigation for CVE-2017-5753.  To be replaced with a
+        * generic mechanism.
+        */
+       asm("lfence");
+
+       if (vmcs_field_to_offset_table[field] == 0)
                return -ENOENT;
 
        return vmcs_field_to_offset_table[field];