From: Andrew Honig <ahonig@google.com>
Date: Wed, 10 Jan 2018 18:12:03 +0000 (-0800)
Subject: KVM: x86: Add memory barrier on vmcs field lookup
X-Git-Tag: v3.2.100~44
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=39a34000fbdf7b64db95112686658662fd723841;p=thirdparty%2Fkernel%2Fstable.git

KVM: x86: Add memory barrier on vmcs field lookup

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 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 346fac6eab9f0..690120f552db9 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -573,8 +573,18 @@ static const int max_vmcs_field = ARRAY_SIZE(vmcs_field_to_offset_table);
 
 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];
 }