linux-kernel - Re: [patch V2 04/25] x86/apic: Make apic_pending_intr

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Date:   Fri, 5 Jul 2019 22:49:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Nadav Amit <namit@...are.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [patch V2 04/25] x86/apic: Make apic_pending_intr_clear() more
 robust

On 05/07/19 22:25, Thomas Gleixner wrote:
> In practice, this makes Linux vulnerable to CVE-2011-1898 / XSA-3, which
> I'm disappointed to see wasn't shared with other software vendors at the
> time.

Oh, that brings back memories.  At the time I was working on Xen, so I
remember that CVE.  IIRC there was some mitigation but the fix was
basically to print a very scary error message if you used VT-d without
interrupt remapping.  Maybe force the user to add something on the Xen
command line too?

> The more interesting question is whether this is all relevant. If I
> understood the issue correctly then this is mitigated by proper interrupt
> remapping.

Yes, and for Linux we're good I think.  VFIO by default refuses to use
the IOMMU if interrupt remapping is absent or disabled, and KVM's own
(pre-VFIO) IOMMU support was removed a couple years ago.  I guess the
secure boot lockdown patches should outlaw VFIO's
allow_unsafe_interrupts option, but that's it.

> Is there any serious usage of virtualization w/o interrupt remapping left
> or have the machines which are not capable been retired already?

I think they were already starting to disappear in 2011, as I don't
remember much worry about customers that were using systems without it.

Paolo