[PATCH 3/3] KVM: SVM: Do not allow SEV/SEV-ES initialization after vCPUs are created

From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>
Subject: [PATCH 3/3] KVM: SVM: Do not allow SEV/SEV-ES initialization after vCPUs are created
Date: Tue, 30 Mar 2021 20:19:36 -0700	[thread overview]
Message-ID: <20210331031936.2495277-4-seanjc@google.com> (raw)
In-Reply-To: <20210331031936.2495277-1-seanjc@google.com>

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 <brijesh.singh@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/sev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 97d42a007b86..824bc7d22e77 100644
--- 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 *kvm, struct kvm_sev_cmd *argp)
 	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;
-- 
2.31.0.291.g576ba9dcdaf-goog

