linux-kernel - Re: [PATCH v6 5/7] KVM: x86: VMX: Prevent MSR passthrough when MSR access is denied

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 16 Sep 2020 13:13:00 -0700
From:   Aaron Lewis <aaronlewis@...gle.com>
To:     Alexander Graf <graf@...zon.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        KarimAllah Raslan <karahmed@...zon.de>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        kvm list <kvm@...r.kernel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/7] KVM: x86: VMX: Prevent MSR passthrough when MSR
 access is denied

> >
> >> +
> >>   /*
> >>    * These 2 parameters are used to config the controls for Pause-Loop Exiting:
> >>    * ple_gap:    upper bound on the amount of time between two successive
> >> @@ -622,6 +642,41 @@ static inline bool report_flexpriority(void)
> >>          return flexpriority_enabled;
> >>   }
> >
> > One thing that seems to be missing is removing MSRs from the
> > permission bitmap or resetting the permission bitmap to its original
> > state before adding changes on top of it.  This would be needed on
> > subsequent calls to kvm_vm_ioctl_set_msr_filter().  When that happens
> > the original changes made by KVM_REQ_MSR_FILTER_CHANGED need to be
> > backed out before applying the new set.
>
> I'm not sure I follow. Subsequent calls to set_msr_filter() will invoke
> the "please reset the whole MSR passthrough bitmap to a consistent
> state" which will then reapply the in-kvm desired state through the
> bitmap and filter state on top on each of those.
>

Yes, you're correct.  I discovered this after the fact by adding a
test to the selftest I wrote for the deny list system which I revamped
to work for your filter system.  It proved the permission bitmaps are
in fact set as expected on subsequent calls.  You can disregard this
comment.

As a side note, I'm happy to share the test if you'd like. I also used
it to uncover an issue in the first commit of this series.