4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Dan Williams <dan.j.willi...@intel.com> (cherry picked from 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.willi...@intel.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Acked-by: Paolo Bonzini <pbonz...@redhat.com> Cc: Andrew Honig <aho...@google.com> Cc: k...@vger.kernel.org Cc: Jim Mattson <jmatt...@google.com> Link: https://lkml.kernel.org/r/151744959670.6342.3001723920950249067.st...@dwillia2-desk3.amr.corp.intel.com Signed-off-by: David Woodhouse <d...@amazon.co.uk> [jwang: cherry pick to 4.4] Signed-off-by: Jack Wang <jinpu.w...@profitbricks.com> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- arch/x86/kvm/vmx.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-) --- 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" @@ -827,21 +828,18 @@ static const unsigned short vmcs_field_t 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)