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

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Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jim Mattson" <jmattson@...gle.com>,
        "Andrew Honig" <ahonig@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>
Subject: [PATCH 3.16 202/254] KVM: x86: Add memory barrier on vmcs field
 lookup

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Andrew Honig <ahonig@...gle.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@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.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];
 }