On Fri, Feb 24, 2023 at 12:42:40PM +0800, Heng Qi wrote:
>
>
> 在 2023/2/23 下午9:13, Michael S. Tsirkin 写道:
> > 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?
>
> I don't understand why it would be risky to just report hash when not used
> for queuing,
> and even we don't report whether hash come from inner or outer now because
> there is no more hash_report_tunnel.
Well what is the hash used for? Presumably it's used for queueing within
driver, no? Collisions there then have exactly the same effect as queue
collisions in the device.
> >
> > > 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)
>
> How a tunnel bit distinguishes between multiple tunnel types, and I think it
> is not so reasonable to use the
> indirection table to determine the switch of the inner hash. The inner hash
> is only the ability to calculate the hash,
> and does not involve the indirection table.
>
> Thanks.
>
> > 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.
> >
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