linux-kernel - [PATCH V2] KVM: SEV: Disable KVM_CAP_VM_COPY_ENC_CONTEXT

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Message-Id: <20210914190125.3289256-1-pgonda@google.com>
Date:   Tue, 14 Sep 2021 12:01:25 -0700
From:   Peter Gonda <pgonda@...gle.com>
To:     kvm@...r.kernel.org
Cc:     Peter Gonda <pgonda@...gle.com>, Marc Orr <marcorr@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Nathan Tempelman <natet@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH V2] KVM: SEV: Disable KVM_CAP_VM_COPY_ENC_CONTEXT_FROM for SEV-ES

Copying an ASID into new vCPUs will not work for SEV-ES since the vCPUs
VMSAs need to be setup and measured before SEV_LAUNCH_FINISH. Return an
error if a users tries to KVM_CAP_VM_COPY_ENC_CONTEXT_FROM from an
SEV-ES guest. The destination VM is already checked for SEV and SEV-ES
with sev_guest(), so this ioctl already fails if the destination is SEV
enabled.

Enabling mirroring a VM or copying its encryption context with an SEV-ES
VM is more involved and should happen in its own feature patch if that's
needed. This is because the vCPUs of SEV-ES VMs need to be updated with
LAUNCH_UPDATE_VMSA before LAUNCH_FINISH. This needs KVM changes because
the mirror VM has all its SEV ioctls blocked and the original VM doesn't
know about the mirrors vCPUs.

Fixes: 54526d1fd593 ("KVM: x86: Support KVM VMs sharing SEV context")

V2:
 * Updated changelog with more information and added stable CC.

Signed-off-by: Peter Gonda <pgonda@...gle.com>
Cc: Marc Orr <marcorr@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Nathan Tempelman <natet@...gle.com>
Cc: Brijesh Singh <brijesh.singh@....com>
Cc: kvm@...r.kernel.org
Cc: stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 arch/x86/kvm/svm/sev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 75e0b21ad07c..8a279027425f 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1728,7 +1728,7 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
 	source_kvm = source_kvm_file->private_data;
 	mutex_lock(&source_kvm->lock);

-	if (!sev_guest(source_kvm)) {
+	if (!sev_guest(source_kvm) || sev_es_guest(source_kvm)) {
 		ret = -EINVAL;
 		goto e_source_unlock;
 	}
-- 
2.33.0.309.g3052b89438-goog