x86/kvm: Be careful not to clear KVM_VCPU_FLUSH_TLB bit

BugLink: https://bugs.launchpad.net/bugs/1866678
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@google.com>)

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 43f953813fb2ed2fad3233615c2655afa86305b6..355b302e9ff7bd4744ff575eb34926e4fbbfdda1 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3098,6 +3098,9 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
        if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
                return;
 
+       if (vcpu->arch.st.steal.preempted)
+               return;
+
        vcpu->arch.st.steal.preempted = 1;
 
        kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime,