netdev - Re: [PATCH net-next v3 2/2] enic: use netdev_dma

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.LNX.2.03.1503111428210.3394@ws.cisco>
Date:	Wed, 11 Mar 2015 14:57:39 +0530 (IST)
From:	Govindarajulu Varadarajan <_govind@....com>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
cc:	Govindarajulu Varadarajan <_govind@....com>, davem@...emloft.net,
	netdev@...r.kernel.org, ssujith@...co.com, benve@...co.com
Subject: Re: [PATCH net-next v3 2/2] enic: use netdev_dma_alloc


On Tue, 10 Mar 2015, Alexander Duyck wrote:

>
> On 03/10/2015 10:43 AM, Govindarajulu Varadarajan wrote:
>> This patches uses dma cache skb allocator fot rx buffers.
>> 
>> netdev_dma_head is initialized per rq. All calls to netdev_dma_alloc_skb() 
>> and
>> netdev_dma_frag_unmap() happens in napi_poll and they are serialized.
>> 
>> Signed-off-by: Govindarajulu Varadarajan <_govind@....com>
>
> This isn't going to work. The problem is the way you are using your fragments 
> you can end up with a memory corruption as the frame headers that were 
> updated by the stack may be reverted for any frames received before the last 
> frame was unmapped.  I ran into that issue when I was doing page reuse with 
> build_skb on the Intel drivers and I suspect you will see the same issue.
>

Is this behaviour platform dependent? I tested this patch for more than a month
and I did not face any issue. I ran normal traffic like ssh, nfs and iperf/netperf.
Is there a special scenario when this could occur?

Will using DMA_BIDIRECTIONAL and sync_to_cpu & sync_to_device solve this?
Each desc should have different dma address to write to. Can you explain me how
this can happen?

> The way to work around it is to receive the data in to the fragments, and 
> then pull the headers out and store them in a separate skb via something 
> similar to copy-break.  You can then track the fragments in frags.
>

If I split the pkt header into another frame, is it guaranteed that stack will
not modify the pkt data?

Thanks a lot for reviewing this patch.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html