linux-kernel - [PATCH 1/3] KVM: SVM: Use online_vcpus, not created

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Message-Id: <20210331031936.2495277-2-seanjc@google.com>
Date:   Tue, 30 Mar 2021 20:19:34 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 1/3] KVM: SVM: Use online_vcpus, not created_vcpus, to iterate
 over vCPUs

Use the kvm_for_each_vcpu() helper to iterate over vCPUs when encrypting
VMSAs for SEV, which effectively switches to use online_vcpus instead of
created_vcpus.  This fixes a possible null-pointer dereference as
created_vcpus does not guarantee a vCPU exists, since it is updated at
the very beginning of KVM_CREATE_VCPU.  created_vcpus exists to allow the
bulk of vCPU creation to run in parallel, while still correctly
restricting the max number of max vCPUs.

Fixes: ad73109ae7ec ("KVM: SVM: Provide support to launch and run an SEV-ES guest")
Cc: stable@...r.kernel.org
Cc: Brijesh Singh <brijesh.singh@....com>
Cc: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/sev.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 83e00e524513..6481d7165701 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -564,6 +564,7 @@ static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
 {
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
 	struct sev_data_launch_update_vmsa *vmsa;
+	struct kvm_vcpu *vcpu;
 	int i, ret;
 
 	if (!sev_es_guest(kvm))
@@ -573,8 +574,8 @@ static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	if (!vmsa)
 		return -ENOMEM;
 
-	for (i = 0; i < kvm->created_vcpus; i++) {
-		struct vcpu_svm *svm = to_svm(kvm->vcpus[i]);
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		struct vcpu_svm *svm = to_svm(vcpu);
 
 		/* Perform some pre-encryption checks against the VMSA */
 		ret = sev_es_sync_vmsa(svm);
-- 
2.31.0.291.g576ba9dcdaf-goog