KVM: SEV: Disallow COPY_ENC_CONTEXT_FROM if target has created vCPUs

Reject COPY_ENC_CONTEXT_FROM if the destination VM has created vCPUs.
KVM relies on SEV activation to occur before vCPUs are created, e.g. to
set VMCB flags and intercepts correctly.

Fixes: 54526d1fd593 ("KVM: x86: Support KVM VMs sharing SEV context")
Cc: stable@vger.kernel.org
Cc: Peter Gonda <pgonda@google.com>
Cc: Marc Orr <marcorr@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Nathan Tempelman <natet@google.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211109215101.2211373-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 3e27698..eeec499 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1775,7 +1775,12 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
        mutex_unlock(&source_kvm->lock);
        mutex_lock(&kvm->lock);
 
-       if (sev_guest(kvm)) {
+       /*
+        * Disallow out-of-band SEV/SEV-ES init if the target is already an
+        * SEV guest, or if vCPUs have been created.  KVM relies on vCPUs being
+        * created after SEV/SEV-ES initialization, e.g. to init intercepts.
+        */
+       if (sev_guest(kvm) || kvm->created_vcpus) {
                ret = -EINVAL;
                goto e_mirror_unlock;
        }