[patch] kvm: sev: Fail KVM_SEV_INIT if already initialized

From: David Rientjes <rientjes@google.com>
To: "Brijesh Singh" <brijesh.singh@amd.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Cc: Thomas Lendacky <Thomas.Lendacky@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [patch] kvm: sev: Fail KVM_SEV_INIT if already initialized
Date: Wed, 2 Jan 2019 12:56:33 -0800 (PST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1901021255410.62182@chino.kir.corp.google.com> (raw)

By code inspection, it was found that multiple calls to KVM_SEV_INIT
could deplete asid bits and overwrite kvm_sev_info's regions_list.

Multiple calls to KVM_SVM_INIT is not likely to occur with QEMU, but this
should likely be fixed anyway.

This code is serialized by kvm->lock.

Fixes: 1654efcbc431 ("KVM: SVM: Add KVM_SEV_INIT command")
Reported-by: Cfir Cohen <cfir@google.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 arch/x86/kvm/svm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -6278,6 +6278,9 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	int asid, ret;
 
 	ret = -EBUSY;
+	if (unlikely(sev->active))
+		return ret;
+
 	asid = sev_asid_new();
 	if (asid < 0)
 		return ret;
