KVM: VMX: Ensure that vmx_create_vcpu always returns proper error

In case certain allocations fail, vmx_create_vcpu may return 0 as error
instead of a negative value encoded via ERR_PTR. This causes a NULL
pointer dereferencing later on in kvm_vm_ioctl_vcpu_create.

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/vmx.c

@@ -4251,8 +4251,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 		goto free_vcpu;
 
 	vmx->guest_msrs = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	err = -ENOMEM;
 	if (!vmx->guest_msrs) {
-		err = -ENOMEM;
 		goto uninit_vcpu;
 	}
 
@@ -4271,7 +4271,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 	if (err)
 		goto free_vmcs;
 	if (vm_need_virtualize_apic_accesses(kvm))
-		if (alloc_apic_access_page(kvm) != 0)
+		err = alloc_apic_access_page(kvm);
+		if (err)
 			goto free_vmcs;
 
 	if (enable_ept) {