[PATCH 3.16 202/254] KVM: x86: Add memory barrier on vmcs field lookup

Ben Hutchings
2018-02-28T16:54:33Z

From: Andrew Honig <ahonig@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 <ahonig@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -698,8 +698,18 @@ static const int max_vmcs_field = ARRAY_

static inline short vmcs_field_to_offset(unsigned long field)
{
- if (field >= max_vmcs_field || vmcs_field_to_offset_table[field] == 0)
+ if (field >= max_vmcs_field)
return -1;
+
+ /*
+ * FIXME: Mitigation for CVE-2017-5753. To be replaced with a
+ * generic mechanism.
+ */
+ asm("lfence");
+
+ if (vmcs_field_to_offset_table[field] == 0)
+ return -1;
+
return vmcs_field_to_offset_table[field];
}