On Tue, 20 Sep 2016 10:39:20 -0700 Eric Dumazet <eric.duma...@gmail.com> wrote:
> On Tue, 2016-09-20 at 09:45 -0700, Alexei Starovoitov wrote: > > > because 'div by zero' is an abnormal situation that shouldn't be exploited. > > Meaning if xdp program is doing DoS prevention and it has a bug that > > attacker can now exploit by sending a crafted packet that causes > > 'div by zero' and kernel will warn then attack got successful. > > Therefore it has to be silent drop. > > A silent drop means a genuine error in a BPF program might be never > caught, since a tracepoint might never be enabled. I do see your point. But we can document our way out of it. > > tracpoint in such case is great, since the user can do debugging with it > > and even monitoring 24/7 and if suddenly the control plan sees a lot > > of such trace_xdp_abotred events, it can disable that tracepoint to avoid > > spam and adjust the program or act on attack some other way. > > Hardcoded warnings and counters are not generic enough for all > > the use cases people want to throw at XDP. > > The tracepoints idea is awesome, in a sense that it's optional. > > > Note that tracepoints are optional in a kernel. Well, that is a good thing, as it can be compiled out (as that provides an option for zero cost). > Many existing supervision infrastructures collect device snmp > counters, and run as unprivileged programs. A supervision infrastructures is a valid use-case. It again indicate that such XDP stats need to structured, not just a random driver specific ethtool counter, to make it easy for such collection daemons. > tracepoints might not fit the need here, compared to a mere > tx_ring->tx_drops++ I do see your point. I really liked the tracepoint idea, but now I'm uncertain again... I do have a use-case where I want to use the NIC HW-RX-ingress-overflow and TX-overflow drop indicators, but I don't want to tie it into this discussion. The abort and error indicators a not relevant for that use-case. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer
