4.15-stable review patch. If anyone has any objections, please let me know.
------------------ From: Dan Williams [email protected] 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 <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Acked-by: Paolo Bonzini <[email protected]> Cc: Andrew Honig <[email protected]> Cc: [email protected] Cc: Jim Mattson <[email protected]> Link: https://lkml.kernel.org/r/151744959670.6342.3001723920950249067.st...@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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 @@ -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_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)
