Messages in this thread Patch in this message | | | Date | Thu, 1 Feb 2018 02:03:50 -0800 | From | tip-bot for Dan Williams <> | Subject | [tip:x86/pti] x86/kvm: Update spectre-v1 mitigation |
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Commit-ID: 085331dfc6bbe3501fb936e657331ca943827600 Gitweb: https://git.kernel.org/tip/085331dfc6bbe3501fb936e657331ca943827600 Author: Dan Williams <dan.j.williams@intel.com> AuthorDate: Wed, 31 Jan 2018 17:47:03 -0800 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Thu, 1 Feb 2018 10:59:10 +0100
x86/kvm: Update spectre-v1 mitigation
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
--- 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 a8b96dc..2894282 100644 --- 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_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)
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