KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest

Intercept RDTSCP to inject #UD if RDTSC is disabled in the guest.

Note, SVM does not support intercepting RDPID.  Unlike VMX's
ENABLE_RDTSCP control, RDTSCP interception does not apply to RDPID.  This
is a benign virtualization hole as the host kernel (incorrectly) sets
MSR_TSC_AUX if RDTSCP is supported, and KVM loads the guest's MSR_TSC_AUX
into hardware if RDTSCP is supported in the host, i.e. KVM will not leak
the host's MSR_TSC_AUX to the guest.

But, when the kernel bug is fixed, KVM will start leaking the host's
MSR_TSC_AUX if RDPID is supported in hardware, but RDTSCP isn't available
for whatever reason.  This leak will be remedied in a future commit.

Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-4-seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index be5cf61..ebcb584 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1100,7 +1100,9 @@ static u64 svm_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
        return svm->vmcb->control.tsc_offset;
 }
 
-static void svm_check_invpcid(struct vcpu_svm *svm)
+/* Evaluate instruction intercepts that depend on guest CPUID features. */
+static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu,
+                                             struct vcpu_svm *svm)
 {
        /*
         * Intercept INVPCID if shadow paging is enabled to sync/free shadow
@@ -1113,6 +1115,13 @@ static void svm_check_invpcid(struct vcpu_svm *svm)
                else
                        svm_clr_intercept(svm, INTERCEPT_INVPCID);
        }
+
+       if (kvm_cpu_cap_has(X86_FEATURE_RDTSCP)) {
+               if (guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
+                       svm_clr_intercept(svm, INTERCEPT_RDTSCP);
+               else
+                       svm_set_intercept(svm, INTERCEPT_RDTSCP);
+       }
 }
 
 static void init_vmcb(struct kvm_vcpu *vcpu)
@@ -1248,7 +1257,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
                svm_clr_intercept(svm, INTERCEPT_PAUSE);
        }
 
-       svm_check_invpcid(svm);
+       svm_recalc_instruction_intercepts(vcpu, svm);
 
        /*
         * If the host supports V_SPEC_CTRL then disable the interception
@@ -3084,6 +3093,7 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
        [SVM_EXIT_STGI]                         = stgi_interception,
        [SVM_EXIT_CLGI]                         = clgi_interception,
        [SVM_EXIT_SKINIT]                       = skinit_interception,
+       [SVM_EXIT_RDTSCP]                       = kvm_handle_invalid_op,
        [SVM_EXIT_WBINVD]                       = kvm_emulate_wbinvd,
        [SVM_EXIT_MONITOR]                      = kvm_emulate_monitor,
        [SVM_EXIT_MWAIT]                        = kvm_emulate_mwait,
@@ -4007,8 +4017,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
        svm->nrips_enabled = kvm_cpu_cap_has(X86_FEATURE_NRIPS) &&
                             guest_cpuid_has(vcpu, X86_FEATURE_NRIPS);
 
-       /* Check again if INVPCID interception if required */
-       svm_check_invpcid(svm);
+       svm_recalc_instruction_intercepts(vcpu, svm);
 
        /* For sev guests, the memory encryption bit is not reserved in CR3.  */
        if (sev_guest(vcpu->kvm)) {