Messages in this thread Patch in this message | | | From | Ben Hutchings <> | Date | Mon, 12 Mar 2018 03:06:12 +0000 | Subject | [PATCH 3.16 62/76] x86/kvm: Update spectre-v1 mitigation |
| |
3.16.56-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Dan Williams <dan.j.williams@intel.com>
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 <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@dwillia2-desk3.amr.corp.intel.com [bwh: Backported to 3.16: - Replace max_vmcs_field with the local size variable - Adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- --- 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" @@ -695,23 +696,21 @@ static const unsigned short vmcs_field_t 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)
| |