KVM: x86: Protect kvm_hv_msr_[get|set]_crash_data() from Spectre-v1/L1TF attacks

This fixes Spectre-v1/L1TF vulnerabilities in kvm_hv_msr_get_crash_data()
and kvm_hv_msr_set_crash_data().
These functions contain index computations that use the
(attacker-controlled) MSR number.

Fixes: e7d9513b ("kvm/x86: added hyper-v crash msrs into kvm hyperv context")
Signed-off-by: Nick Finco <nifi@google.com>
Signed-off-by: Marios Pomonis <pomonis@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/hyperv.c

@@ -810,11 +810,12 @@ static int kvm_hv_msr_get_crash_data(struct kvm_vcpu *vcpu,
 				     u32 index, u64 *pdata)
 {
 	struct kvm_hv *hv = &vcpu->kvm->arch.hyperv;
+	size_t size = ARRAY_SIZE(hv->hv_crash_param);
 
-	if (WARN_ON_ONCE(index >= ARRAY_SIZE(hv->hv_crash_param)))
+	if (WARN_ON_ONCE(index >= size))
 		return -EINVAL;
 
-	*pdata = hv->hv_crash_param[index];
+	*pdata = hv->hv_crash_param[array_index_nospec(index, size)];
 	return 0;
 }
 
@@ -853,11 +854,12 @@ static int kvm_hv_msr_set_crash_data(struct kvm_vcpu *vcpu,
 				     u32 index, u64 data)
 {
 	struct kvm_hv *hv = &vcpu->kvm->arch.hyperv;
+	size_t size = ARRAY_SIZE(hv->hv_crash_param);
 
-	if (WARN_ON_ONCE(index >= ARRAY_SIZE(hv->hv_crash_param)))
+	if (WARN_ON_ONCE(index >= size))
 		return -EINVAL;
 
-	hv->hv_crash_param[index] = data;
+	hv->hv_crash_param[array_index_nospec(index, size)] = data;
 	return 0;
 }