3.16.56-rc1 review patch. If anyone has any objections, please let me know.
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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@dwilli... [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)