[dpdk-dev] [PATCH] vhost: fix segfault on bad descriptor address.

Yuanhan Liu yuanhan.liu at linux.intel.com
Mon May 30 16:25:40 CEST 2016


Hi Ilya,

Generically speaking, this patch looks good to me. But I guess still
need more time to check this issue later; I still failed to reproduce
it on my side after all. So, please allow a late merge.

Thanks.

	--yliu

On Mon, May 30, 2016 at 02:05:07PM +0300, Ilya Maximets wrote:
> Ping.
> 
> Best regards, Ilya Maximets.
> 
> On 23.05.2016 14:04, Ilya Maximets wrote:
> > On 23.05.2016 13:57, Yuanhan Liu wrote:
> >> On Fri, May 20, 2016 at 03:50:04PM +0300, Ilya Maximets wrote:
> >>> In current implementation guest application can reinitialize vrings
> >>> by executing start after stop. In the same time host application
> >>> can still poll virtqueue while device stopped in guest and it will
> >>> crash with segmentation fault while vring reinitialization because
> >>> of dereferencing of bad descriptor addresses.
> >>>
> >>> OVS crash for example:
> >>> <------------------------------------------------------------------------>
> >>> [test-pmd inside guest VM]
> >>>
> >>> 	testpmd> port stop all
> >>> 	    Stopping ports...
> >>> 	    Checking link statuses...
> >>> 	    Port 0 Link Up - speed 10000 Mbps - full-duplex
> >>> 	    Done
> >>> 	testpmd> port config all rxq 2
> >>> 	testpmd> port config all txq 2
> >>> 	testpmd> port start all
> >>> 	    Configuring Port 0 (socket 0)
> >>> 	    Port 0: 52:54:00:CB:44:C8
> >>> 	    Checking link statuses...
> >>> 	    Port 0 Link Up - speed 10000 Mbps - full-duplex
> >>> 	    Done
> >>
> >> I actually didn't manage to reproduce it on my side, with the
> >> vhost-example instead of OVS though. Is that all the commands
> >> to reproduce it, and run them just after start test-pmd?
> > 
> > Actually, I think, packet flow should be enabled while performing
> > above actions and some traffic already should be sent through port
> > to change last used idx on vhost side.
> > 
> > Something like:
> > 	start
> > 	..wait a while.. see that packets are flowing.
> > 	stop
> > 	port stop
> > 	port config
> > 	port config
> > 	port start
> >>
> >>> [OVS on host]
> >>> 	Program received signal SIGSEGV, Segmentation fault.
> >>> 	rte_memcpy (n=2056, src=0xc, dst=0x7ff4d5247000) at rte_memcpy.h
> >>>
> >>> 	(gdb) bt
> >>> 	    #0  rte_memcpy (n=2056, src=0xc, dst=0x7ff4d5247000)
> >>> 	    #1  copy_desc_to_mbuf
> >>> 	    #2  rte_vhost_dequeue_burst
> >>> 	    #3  netdev_dpdk_vhost_rxq_recv
> >>> 	    ...
> >>>
> >>> 	(gdb) bt full
> >>> 	    #0  rte_memcpy
> >>> 	        ...
> >>> 	    #1  copy_desc_to_mbuf
> >>> 	        desc_addr = 0
> >>> 	        mbuf_offset = 0
> >>> 	        desc_offset = 12
> >>> 	        ...
> >>> <------------------------------------------------------------------------>
> >>>
> >>> Fix that by checking addresses of descriptors before using them.
> >>>
> >>> Note: For mergeable buffers this patch checks only guest's address for
> >>> zero, but in non-meargeable case host's address checked. This is done
> >>> because checking of host's address in mergeable case requires additional
> >>> refactoring to keep virtqueue in consistent state in case of error.
> >>>
> >>> Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
> >>> ---
> >>>
> >>> Actually, current virtio implementation looks broken for me. Because
> >>> 'virtio_dev_start' breaks virtqueue while it still available from the vhost
> >>> side.
> >>>
> >>> There was 2 patches about this behaviour:
> >>>
> >>> 	1. a85786dc816f ("virtio: fix states handling during initialization")
> >>> 	2. 9a0615af7746 ("virtio: fix restart")
> >>>
> >>> The second patch fixes somehow issue intoduced in the first patch, but actually
> >>> also breaks vhost in the way described above.
> >>> It's not pretty clear for me what to do in current situation with virtio,
> >>> because it will be broken for guest application even if vhost will not crash.
> >>>
> >>> May be it'll be better to forbid stopping of virtio device and force user to
> >>> exit and start again (may be implemented in hidden from user way)?
> >>>
> >>> This patch adds additional sane checks, so it should be applied anyway, IMHO.
> >>
> >> Agreed.
> >>
> >> 	--yliu
> >>
> >>


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