netdev - RE: [net-next PATCH v1 1/3] net: sched: af_packet support for direct ring access

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Date:	Fri, 10 Oct 2014 03:49:23 +0000
From:	"Zhou, Danny" <danny.zhou@...el.com>
To:	David Miller <davem@...emloft.net>
CC:	"willemb@...gle.com" <willemb@...gle.com>,
	"john.fastabend@...il.com" <john.fastabend@...il.com>,
	"dborkman@...hat.com" <dborkman@...hat.com>,
	"fw@...len.de" <fw@...len.de>,
	"gerlitz.or@...il.com" <gerlitz.or@...il.com>,
	"hannes@...essinduktion.org" <hannes@...essinduktion.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"amirv@...lanox.com" <amirv@...lanox.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: RE: [net-next PATCH v1 1/3] net: sched: af_packet support for
 direct ring access


> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Wednesday, October 08, 2014 12:06 AM
> To: Zhou, Danny
> Cc: willemb@...gle.com; john.fastabend@...il.com; dborkman@...hat.com; fw@...len.de; gerlitz.or@...il.com;
> hannes@...essinduktion.org; netdev@...r.kernel.org; Ronciak, John; amirv@...lanox.com; eric.dumazet@...il.com
> Subject: Re: [net-next PATCH v1 1/3] net: sched: af_packet support for direct ring access
> 
> From: "Zhou, Danny" <danny.zhou@...el.com>
> Date: Tue, 7 Oct 2014 15:21:15 +0000
> 
> > Once qpairs split-off is done, the user space driver, as a slave
> > driver, will re-initialize those queues completely in user space by
> > using paddr(in the case of DPDK, vaddr of DPDK used huge pages are
> > translated to paddr) to fill in the packet descriptors.  As of
> > security concern raised in previous discussion, the reason we
> > think(BTW, correct me if I am wrong) af_packet is most suitable is
> > because only user application with root permission is allowed to
> > successfully split-off queue pairs and mmap a small window of PCIe
> > I/O space to user space, so concern regarding "device can DMA
> > from/to any arbitrary physical memory." is not that big. As all user
> > space device drivers based on UIO mechanism has the same concern
> > issue, VFIO adds protection but it is based on IOMMU which is
> > specific to Intel silicons.
> 
> Wait a second.
> 
> If there is no memory protection performed I'm not merging this.
> 
> I thought the user has to associate a fixed pool of memory to the
> queueus, the kernel attaches that memory, and then the user cannot
> modify the addresses _AT_ _ALL_.
> 
> If the user can modify the addresses in the descriptors and make
> the chip crap on random memory, this is a non-starter.
> 
> Sorry.

Fairly enough, we will manage to add memory protection in future versions. 
Several options are under investigation.


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