linux-kernel - [PATCH 5.4 214/309] x86/kvm: Be careful not to clear KVM_VCPU_FLUSH

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Date:   Mon, 10 Feb 2020 04:32:50 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.4 214/309] x86/kvm: Be careful not to clear KVM_VCPU_FLUSH_TLB bit

From: Boris Ostrovsky <boris.ostrovsky@...cle.com>

commit 8c6de56a42e0c657955e12b882a81ef07d1d073e upstream.

kvm_steal_time_set_preempted() may accidentally clear KVM_VCPU_FLUSH_TLB
bit if it is called more than once while VCPU is preempted.

This is part of CVE-2019-3016.

(This bug was also independently discovered by Jim Mattson
<jmattson@...gle.com>)

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Reviewed-by: Joao Martins <joao.m.martins@...cle.com>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/x86.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3499,6 +3499,9 @@ static void kvm_steal_time_set_preempted
 	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
 		return;
 
+	if (vcpu->arch.st.steal.preempted)
+		return;
+
 	vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
 
 	kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime,