Re: Re: Xen Security Advisory 467 v1 (CVE-2025-1713) - deadlock potential with VT-d and legacy PCI device pass-through

[Demi Marie Obenour <demi () invisiblethingslab com>]

On Thu, Feb 27, 2025 at 03:33:18PM +0000, Teddy Astie wrote:
> Hello,
>
> Le 27/02/2025 à 13:57, Xen.org security team a écrit :
> >              Xen Security Advisory CVE-2025-1713 / XSA-467
> >
> >      deadlock potential with VT-d and legacy PCI device pass-through
> >
> > ISSUE DESCRIPTION
> > =================
> >
> > When setting up interrupt remapping for legacy PCI(-X) devices,
> > including PCI(-X) bridges, a lookup of the upstream bridge is required.
> > This lookup, itself involving acquiring of a lock, is done in a context
> > where acquiring that lock is unsafe.  This can lead to a deadlock.
> >
> > IMPACT
> > ======
> >
> > The passing through of certain kinds of devices to an unprivileged guest
> > can result in a Denial of Service (DoS) affecting the entire host.
> >
> > Note: Normal usage of such devices by a privileged domain can also
> >        trigger the issue.  In such a scenario, the deadlock is not
> >        considered a security issue, but just a plain bug.
> >
> > VULNERABLE SYSTEMS
> > ==================
> >
> > Xen versions 4.0 and later are affected.  Xen versions 3.4 and earlier
> > are not directly affected, but had other issues.
> >
> > Systems with Intel IOMMU hardware (VT-d) are affected.  Systems using
> > AMD or non-x86 hardware are not affected.
> >
> > Only systems where certain kinds of devices are passed through to an
> > unprivileged guest are vulnerable.
> >
> > MITIGATION
> > ==========
> >
> > Avoiding the passing through of the affected device types will avoid
> > the vulnerability.
>
> Is disabling interrupt remapping another way of mitigating this
> vulnerability (e.g iommu=no-intremap) ?

No, as this allows other attacks that allow denial of service at the
very least.  See
https://lore.kernel.org/xen-devel/19915.58644.191837.671729 () mariner uk xensource com/.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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