Re: [patch V2 04/25] x86/apic: Make apic_pending_intr_clear() more robust

From: Paolo Bonzini
Date: Fri Jul 05 2019 - 16:50:01 EST

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.