linux-kernel - Re: [PATCH RFC net-next 13/14] samples: bpf: example of stateful socket filtering

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Date:	Fri, 27 Jun 2014 17:21:07 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 13/14] samples: bpf: example of stateful
 socket filtering

On Fri, Jun 27, 2014 at 5:06 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
> this socket filter example does:
>
> - creates a hashtable in kernel with key 4 bytes and value 8 bytes
>
> - populates map[6] = 0; map[17] = 0;  // 6 - tcp_proto, 17 - udp_proto
>
> - loads eBPF program:
>   r0 = skb[14 + 9]; // load one byte of ip->proto
>   *(u32*)(fp - 4) = r0;
>   value = bpf_map_lookup_elem(map_id, fp - 4);
>   if (value)
>        (*(u64*)value) += 1;

In the code below, this is XADD.  Is there anything that validates
that shared things like this can only be poked at by atomic
operations?

--Andy
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