From: Dan Williams dan.j.williams@intel.com
This patch has been added to the 4.1 stable tree. If you have any objections, please let us know.
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[ Upstream commit 085331dfc6bbe3501fb936e657331ca943827600 ]
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'.
The lfence can be avoided in this path by using the array_index_nospec() helper designed for these types of fixes.
Signed-off-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Acked-by: Paolo 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@dwilli... Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- 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 6092e6c83de0..e8f34eaac2c8 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -32,6 +32,7 @@ #include <linux/slab.h> #include <linux/tboot.h> #include <linux/hrtimer.h> +#include <linux/nospec.h> #include "kvm_cache_regs.h" #include "x86.h"
@@ -770,21 +771,18 @@ 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)