Commit 085331df authored by Dan Williams's avatar Dan Williams Committed by Thomas Gleixner
Browse files

x86/kvm: Update spectre-v1 mitigation

Commit 75f139aa

 "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'.

The lfence can be avoided in this path by using the array_index_nospec()
helper designed for these types of fixes.

Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Cc: Andrew Honig <ahonig@google.com>
Cc: kvm@vger.kernel.org
Cc: Jim Mattson <jmattson@google.com>
Link: https://lkml.kernel.org/r/151744959670.6342.3001723920950249067.stgit@dwillia2-desk3.amr.corp.intel.com
parent 12c69f1e
......@@ -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)
......
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