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From:   Jiang Jiasheng <jiasheng@iscas.ac.cn>
To:     pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com,
        wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        hpa@zytor.com, jarkko@kernel.org, dave.hansen@linux.intel.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-sgx@vger.kernel.org, Jiang Jiasheng <jiasheng@iscas.ac.cn>
Subject: [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
Date:   Fri,  3 Sep 2021 07:55:00 +0000
Message-Id: <1630655700-798374-1-git-send-email-jiasheng@iscas.ac.cn>
Precedence: bulk

The kvm_get_vcpu() will call for the array_index_nospec()
with the value of atomic_read(&(v->kvm)->online_vcpus) as size,
and the value of constant '0' as index.
If the size is also '0', it will be unreasonabe
that the index is no less than the size.

Signed-off-by: Jiang Jiasheng <jiasheng@iscas.ac.cn>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0f4a46..c59013c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2871,7 +2871,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 				       offsetof(struct compat_vcpu_info, time));
 	if (vcpu->xen.vcpu_time_info_set)
 		kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0);
-	if (v == kvm_get_vcpu(v->kvm, 0))
+	if (atomic_read(&(v->kvm)->online_vcpus) > 0 && v == kvm_get_vcpu(v->kvm, 0))
 		kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
 	return 0;
 }
-- 
2.7.4