Messages in this thread | | | Date | Tue, 06 Oct 2015 20:03:55 +0200 | From | Daniel Borkmann <> | Subject | Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs |
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On 10/06/2015 07:50 PM, Alexei Starovoitov wrote: > On 10/6/15 1:39 AM, Daniel Borkmann wrote: >>>> [...] Also classic BPF would then need to test for it, since a socket >>>> filter >>>> doesn't really know whether native eBPF is loaded there or a >>>> classic-to-eBPF >>>> transformed one, and classic never makes use of this. Anyway, it >>>> could be done >>>> by adding a bit flag cb_access:1 to the bpf_prog, set it during eBPF >>>> verification phase, and test it inside sk_filter() if I see it >>>> correctly. >>> >>> That could also be done in an unlikely() branch, to keep the cost to >>> the non-eBPF >>> case near zero. >> >> Yes, agreed. For the time being, the majority of users are coming from the >> classic BPF side anyway and the unlikely() could still be changed later on >> if it should not be the case anymore. The flag and bpf_func would share the >> same cacheline as well. > > was also thinking that we can do it only in paths that actually > have multiple protocol layers, since today bpf is mainly used with > tcpdump(raw_socket) and new af_packet fanout both have cb cleared > on RX, because it just came out of alloc_skb and no layers were called, > and on TX we can clear 20 bytes in dev_queue_xmit_nit(). > af_unix/netlink also have clean skb. Need to analyze tun and sctp... > but it feels overly fragile to save a branch in sk_filter, > so planning to go with > if(unlikely(prog->cb_access)) memset in sk_filter().
I was also thinking that for dev_queue_xmit_nit(), since we do the skb_clone() there, to have a clone version (w/o affecting performance of the current one) that instead of copying cb[] over, it would just do a memset(). But that would just be limited to AF_PACKET, and doesn't catch all sk_filter() users.
Thanks, Daniel
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