x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest

Expose the CPUID.7.EDX[31] bit to the guest, and also guard against various
combinations of SPEC_CTRL MSR values.

The handling of the MSR (to take into account the host value of SPEC_CTRL
Bit(2)) is taken care of in patch:

  KVM/SVM/VMX/x86/spectre_v2: Support the combination of guest and host IBRS

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
CVE-2018-3639 (x86)

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 37b6ced2b2313126ee3dc5f6f5058e91ce6713b3..daed3050e2de8e2a01b71c151a7a6b941f27a820 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -395,7 +395,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
        /* cpuid 7.0.edx*/
        const u32 kvm_cpuid_7_0_edx_x86_features =
-               F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
+               F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) | F(RDS) |
                F(ARCH_CAPABILITIES);
 
        /* all calls to cpuid_count() should be made on the same cpu */

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a3e3e67b5574aac364f1be765c626c74fa46b411..dcf2a2d34b39b5b4f8fa0492c5170f06cc07ef3f 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3297,7 +3297,8 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
        case MSR_IA32_SPEC_CTRL:
                if (!msr_info->host_initiated &&
                    !guest_cpuid_has(vcpu, X86_FEATURE_IBRS) &&
-                   !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+                   !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
+                   !guest_cpuid_has(vcpu, X86_FEATURE_RDS))
                        return 1;
 
                msr_info->data = to_vmx(vcpu)->spec_ctrl;
@@ -3418,11 +3419,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
        case MSR_IA32_SPEC_CTRL:
                if (!msr_info->host_initiated &&
                    !guest_cpuid_has(vcpu, X86_FEATURE_IBRS) &&
-                   !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+                   !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
+                   !guest_cpuid_has(vcpu, X86_FEATURE_RDS))
                        return 1;
 
                /* The STIBP bit doesn't fault even if it's not advertised */
-               if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))
+               if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_RDS))
                        return 1;
 
                vmx->spec_ctrl = data;