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Re: Security support status of xnf(4) and xbf(4)
- To: Chris Cappuccio <chris@xxxxxxxxxx>, Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Fri, 25 Mar 2022 23:50:24 +0000
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Marek Marczykowski-G?recki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Xen developer discussion <xen-devel@xxxxxxxxxxxxxxxxxxxx>, OpenBSD technical mailing list <tech@xxxxxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHYQGN+XBaov1qn+kGEeGg+qt+r9qzQsngAgAAS8IA=
- Thread-topic: Security support status of xnf(4) and xbf(4)
On 25/03/2022 22:42, Chris Cappuccio wrote:
> Demi Marie Obenour [demi@xxxxxxxxxxxxxxxxxxxxxx] wrote:
>> Linux???s netfront and blkfront drivers recently had a security
>> vulnerability (XSA-396) that allowed a malicious backend to potentially
>> compromise them. In follow-up audits, I found that OpenBSD???s xnf(4)
>> currently trusts the backend domain. I reported this privately to Theo
>> de Raadt, who indicated that OpenBSD does not consider this to be a
>> security concern.
>>
> A malicious backend could completely compromise the virtual host in an
> infinite number of ways.
Xen PV front/back pairs have had far better security
properties/guarantees for longer than virtio has existed. Under the Xen
architecture, the backend has never had the ability to "DMA" to areas
which aren't explicitly permitted by the frontend.
If a frontend handles it's grants correctly, then it need only trust Xen
but not the backend for any problems beyond "backend refuses to transmit
data".
The backend can of course cease transmitting data. That's mitigated
with market pressures of "OK I'll take my credit card elsewhere". Data
integrity issues can be mitigated by using encryption techniques.
With the advent of encrypted VM technologies (AMD SEV-SNP, Intel TXT)
the VM need not trust Xen any further than "will continue to schedule
you" which equally is mitigated with market pressures related to money.
~Andrew
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