linux-kernel - [PATCH] x86/kvm: Update spectre-v1 mitigation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <151744959670.6342.3001723920950249067.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Wed, 31 Jan 2018 17:47:03 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     tglx@...utronix.de
Cc:     Andrew Honig <ahonig@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH] x86/kvm: Update spectre-v1 mitigation

Commit 75f139aaf896 "KVM: x86: Add memory barrier on vmcs field lookup"
added a raw 'asm("lfence");' to prevent a bounds check bypass of
'vmcs_field_to_offset_table'. We can save an lfence in this path and
just use the common array_index_nospec() helper designed for these types
of fixes.

Cc: Andrew Honig <ahonig@...gle.com>
Cc: Jim Mattson <jmattson@...gle.com>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
Hi Thomas,

Here's that KVM patch rebased on latest tip/x86/pti.

 arch/x86/kvm/vmx.c |   20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a8b96dc4cd83..28942823cc3a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -34,6 +34,7 @@
 #include <linux/tboot.h>
 #include <linux/hrtimer.h>
 #include <linux/frame.h>
+#include <linux/nospec.h>
 #include "kvm_cache_regs.h"
 #include "x86.h"
 
@@ -898,21 +899,18 @@ static const unsigned short vmcs_field_to_offset_table[] = {
 
 static inline short vmcs_field_to_offset(unsigned long field)
 {
-	BUILD_BUG_ON(ARRAY_SIZE(vmcs_field_to_offset_table) > SHRT_MAX);
+	const size_t size = ARRAY_SIZE(vmcs_field_to_offset_table);
+	unsigned short offset;
 
-	if (field >= ARRAY_SIZE(vmcs_field_to_offset_table))
+	BUILD_BUG_ON(size > SHRT_MAX);
+	if (field >= size)
 		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)
+	field = array_index_nospec(field, size);
+	offset = vmcs_field_to_offset_table[field];
+	if (offset == 0)
 		return -ENOENT;
-
-	return vmcs_field_to_offset_table[field];
+	return offset;
 }
 
 static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)