Re: [PATCH v9] virtio-net: support inner header hash

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Feb 18, 2023 at 10:37:15PM +0800, Heng Qi wrote:
> +\subparagraph{Security risks between encapsulated packets and RSS}
> +There may be potential security risks when encapsulated packets using RSS to
> +select queues for placement.

Is this just with RSS? I assume hash calculation is also used for
something like queueing so there's a similar risk even just
with hash reporting, no?


> When a user inside a tunnel tries to control the
> +enqueuing of encapsulated packets, then the user can flood the device with invaild
> +packets, and the flooded packets may be hashed into the same queue as packets in
> +other normal tunnels, which causing the queue to overflow.
> +
> +This can pose several security risks:
> +\begin{itemize}
> +\item  Encapsulated packets in the normal tunnels cannot be enqueued due to queue
> +       overflow, resulting in a large amount of packet loss.
> +\item  The delay and retransmission of packets in the normal tunnels are extremely increased.
> +\item  The user can observe the traffic information and enqueue information of other normal
> +       tunnels, and conduct targeted DoS attacks.
> +\end{\itemize}
> +


So for RSS specifically, we brain-stormed with Amnon (Cc'd) and came
up with an idea: RSS indirection table entries are 16 bit but
onlu 15 bits are used to indentify an RX queue.
We can use the remaining bit as a "tunnel bit" to signal whether to use the
inner or the outer hash for queue selection.

The lookup will work like this then:

calculate outer hash
if (rss[outer hash] & tunnel bit)
then
	calculate inner hash
	return rss[inner hash] & ~tunnel bit
else
	return rss[outer hash]


this fixes the security issue returning us back to
status quo : specific tunnels can be directed to separate queues.


This is for RSS.


For hash reporting indirection table is not used.
Maybe it is enough to signal to driver that inner hash was used.
We do need that signalling though.

My question would be whether it's practical to implement in hardware.

-- 
MST