oss-security - Re: Xen Security Advisory 329 v2 - Linux ioperm bitmap context switching issues

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Message-ID: <CAA8xKjVib9UERsMrAy3nNdVssNxLciXTmmhmXqq1gvhO16URew@mail.gmail.com>
Date: Fri, 17 Jul 2020 09:54:21 +0200
From: Mauro Matteo Cascella <mcascell@...hat.com>
To: oss-security@...ts.openwall.com
Cc: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, 
	xen-users@...ts.xen.org, 
	"Xen.org security team" <security-team-members@....org>
Subject: Re: Xen Security Advisory 329 v2 - Linux ioperm bitmap
 context switching issues

Hello,

Will a CVE be assigned to this flaw?

Thanks,

On Thu, Jul 16, 2020 at 3:21 PM Xen.org security team <security@....org>
wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
>
>                     Xen Security Advisory XSA-329
>                               version 2
>
>              Linux ioperm bitmap context switching issues
>
> UPDATES IN VERSION 2
> ====================
>
> Public release.
>
> ISSUE DESCRIPTION
> =================
>
> Linux 5.5 overhauled the internal state handling for the iopl() and
> ioperm()
> system calls.  Unfortunately, one aspect on context switch wasn't wired up
> correctly for the Xen PVOps case.
>
> IMPACT
> ======
>
> IO port permissions don't get rescinded when context switching to an
> unprivileged task.  Therefore, all userspace can use the IO ports granted
> to
> the most recently scheduled task with IO port permissions.
>
> VULNERABLE SYSTEMS
> ==================
>
> Only x86 guests are vulnerable.
>
> All versions of Linux from 5.5 are potentially vulnerable.
>
> Linux is only vulnerable when running as x86 PV guest.  Linux is not
> vulnerable when running as an x86 HVM/PVH guests.
>
> The vulnerability can only be exploited in domains which have been granted
> access to IO ports by Xen.  This is typically only the hardware domain, and
> guests configured with PCI Passthrough.
>
> MITIGATION
> ==========
>
> Running only HVM/PVH guests avoids the vulnerability.
>
> CREDITS
> =======
>
> This issue was discovered by Andy Lutomirski.
>
> RESOLUTION
> ==========
>
> Applying the appropriate attached patch resolves this issue.
>
> xsa329.patch           Linux 5.5 and later
>
> $ sha256sum xsa329*
> cdb5ac9bfd21192b5965e8ec0a1c4fcf12d0a94a962a8158cd27810e6aa362f0
> xsa329.patch
> $
>
> DEPLOYMENT DURING EMBARGO
> =========================
>
> Deployment of the patches and/or mitigations described above (or
> others which are substantially similar) is permitted during the
> embargo, even on public-facing systems with untrusted guest users and
> administrators.
>
> But: Distribution of updated software is prohibited (except to other
> members of the predisclosure list).
>
> Predisclosure list members who wish to deploy significantly different
> patches and/or mitigations, please contact the Xen Project Security
> Team.
>
>
> (Note: this during-embargo deployment notice is retained in
> post-embargo publicly released Xen Project advisories, even though it
> is then no longer applicable.  This is to enable the community to have
> oversight of the Xen Project Security Team's decisionmaking.)
>
> For more information about permissible uses of embargoed information,
> consult the Xen Project community's agreed Security Policy:
>   http://www.xenproject.org/security-policy.html
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>


-- 
Mauro Matteo Cascella, Red Hat Product Security
6F78 E20B 5935 928C F0A8  1A9D 4E55 23B8 BB34 10B0

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