netdev - Re: [PATCH iwl-next v4 09/12] ice: Save and load TX Queue head

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Date: Thu, 7 Dec 2023 10:48:07 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: "Cao, Yahui" <yahui.cao@...el.com>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Liu, Lingyu" <lingyu.liu@...el.com>,
	"Chittim, Madhu" <madhu.chittim@...el.com>,
	"Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"yishaih@...dia.com" <yishaih@...dia.com>,
	"shameerali.kolothum.thodi@...wei.com" <shameerali.kolothum.thodi@...wei.com>,
	"brett.creeley@....com" <brett.creeley@....com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>
Subject: Re: [PATCH iwl-next v4 09/12] ice: Save and load TX Queue head

On Thu, Dec 07, 2023 at 08:22:53AM +0000, Tian, Kevin wrote:
> > In virtual channel model, VF driver only send TX queue ring base and
> > length info to PF, while rest of the TX queue context are managed by PF.
> > TX queue length must be verified by PF during virtual channel message
> > processing. When PF uses dummy descriptors to advance TX head, it will
> > configure the TX ring base as the new address managed by PF itself. As a
> > result, all of the TX queue context is taken control of by PF and this
> > method won't generate any attacking vulnerability
> 
> So basically the key points are:
> 
> 1) TX queue head cannot be directly updated via VF mmio interface;
> 2) Using dummy descriptors to update TX queue head is possible but it
>     must be done in PF's context;
> 3) FW provides a way to keep TX queue head intact when moving
>     the TX queue ownership between VF and PF;
> 4) the TX queue context affected by the ownership change is largely
>     initialized by the PF driver already, except ring base/size coming from
>     virtual channel messages. This implies that a malicious guest VF driver
>     cannot attack this small window though the tx head restore is done
>     after all the VF state are restored;
> 5) and a missing point is that the temporary owner change doesn't
>     expose the TX queue to the software stack on top of the PF driver
>     otherwise that would be a severe issue.

This matches my impression of these patches. It is convoluted but the
explanation sounds find, and if Intel has done an internal security
review then I have no issue.

Jason