From eba7e6e7249cfaf779eb1e19bad1a3feff01b758 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Wed, 31 Jan 2018 17:47:03 -0800 Subject: [PATCH] x86/kvm: Update spectre-v1 mitigation commit 085331dfc6bbe3501fb936e657331ca943827600 upstream. 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 Signed-off-by: Thomas Gleixner Acked-by: Paolo Bonzini Cc: Andrew Honig Cc: kvm@vger.kernel.org Cc: Jim Mattson Link: https://lkml.kernel.org/r/151744959670.6342.3001723920950249067.stgit@dwillia2-desk3.amr.corp.intel.com [bwh: Backported to 3.2: - Replace max_vmcs_field with the local size variable - Adjust context] Signed-off-by: Ben Hutchings --- arch/x86/kvm/vmx.c | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 00ad49780230..24227a820ee3 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -29,6 +29,7 @@ #include #include #include +#include #include "kvm_cache_regs.h" #include "x86.h" @@ -570,23 +571,21 @@ static unsigned short vmcs_field_to_offset_table[] = { FIELD(HOST_RSP, host_rsp), FIELD(HOST_RIP, host_rip), }; -static const int max_vmcs_field = ARRAY_SIZE(vmcs_field_to_offset_table); static inline short vmcs_field_to_offset(unsigned long field) { - if (field >= max_vmcs_field) - return -1; + const size_t size = ARRAY_SIZE(vmcs_field_to_offset_table); + unsigned short offset; - /* - * FIXME: Mitigation for CVE-2017-5753. To be replaced with a - * generic mechanism. - */ - asm("lfence"); - - if (vmcs_field_to_offset_table[field] == 0) + BUILD_BUG_ON(size > SHRT_MAX); + if (field >= size) return -1; - return vmcs_field_to_offset_table[field]; + field = array_index_nospec(field, size); + offset = vmcs_field_to_offset_table[field]; + if (offset == 0) + return -1; + return offset; } static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu) -- 2.39.2