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[v5,10/12] kvm, x86: update spectre-v1 mitigation

Message ID 151703976714.26578.17488222459772354305.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Dan Williams Jan. 27, 2018, 7:56 a.m. UTC 
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_idx' helper designed for these types of
fixes.

Cc: Andrew Honig <ahonig@google.com>
Cc: Jim Mattson <jmattson@google.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/x86/kvm/vmx.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)
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Patch

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 924589c53422..5345e68cc506 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"
 
@@ -883,13 +884,18 @@  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 sz = ARRAY_SIZE(vmcs_field_to_offset_table);
+	unsigned short offset;
 
-	if (field >= ARRAY_SIZE(vmcs_field_to_offset_table) ||
-	    vmcs_field_to_offset_table[field] == 0)
+	BUILD_BUG_ON(sz > SHRT_MAX);
+	if (field >= sz)
 		return -ENOENT;
 
-	return vmcs_field_to_offset_table[field];
+	field = array_idx(field, sz);
+	offset = vmcs_field_to_offset_table[field];
+	if (offset == 0)
+		return -ENOENT;
+	return offset;
 }
 
 static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)