From: Sean Christopherson <seanjc@google.com>

commit 8727906fde6ea665b52e68ddc58833772537f40a upstream.

Reject KVM_SEV_INIT and KVM_SEV_ES_INIT if they are attempted after one
or more vCPUs have been created.  KVM assumes a VM is tagged SEV/SEV-ES
prior to vCPU creation, e.g. init_vmcb() needs to mark the VMCB as SEV
enabled, and svm_create_vcpu() needs to allocate the VMSA.  At best,
creating vCPUs before SEV/SEV-ES init will lead to unexpected errors
and/or behavior, and at worst it will crash the host, e.g.
sev_launch_update_vmsa() will dereference a null svm->vmsa pointer.

Fixes: 1654efcbc431 ("KVM: SVM: Add KVM_SEV_INIT command")
Fixes: ad73109ae7ec ("KVM: SVM: Provide support to launch and run an SEV-ES guest")
Cc: stable@vger.kernel.org
Cc: Brijesh Singh <redacted>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: [off-list ref]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kvm/svm/sev.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c

@@ -182,6 +182,9 @@ static int sev_guest_init(struct kvm *kv
 	bool es_active = argp->id == KVM_SEV_ES_INIT;
 	int asid, ret;
 
+	if (kvm->created_vcpus)
+		return -EINVAL;
+
 	ret = -EBUSY;
 	if (unlikely(sev->active))
 		return ret;