From: Daniel Borkmann <daniel@iogearbox•net>
To: Johannes Berg <johannes@sipsolutions•net>
Cc: "netdev@vger•kernel.org" <netdev@vger•kernel.org>,
Alexei Starovoitov <ast@kernel•org>
Subject: Re: eBPF - little-endian load instructions?
Date: Tue, 11 Apr 2017 13:22:40 +0200 [thread overview]
Message-ID: <58ECBC80.1050009@iogearbox.net> (raw)
In-Reply-To: <1491909330.31620.21.camel@sipsolutions.net>
On 04/11/2017 01:15 PM, Johannes Berg wrote:
>
>> Are you working with an skb at that point in time in wifi?
>
> Yes.
>
>> There are
>> 3 different ways of accessing skb data, see [1] slide 7 - 10. The BPF
>> LD_ABS/IND instructions were carried over from cBPF and are the only
>> ones that convert to host endianess. It can be used in eBPF as well,
>> but there are more efficient ways like 'direct packet access' or
>> helpers such as bpf_skb_load_bytes() that load the raw buffers as-is,
>> which is probably what you want if I understand you correctly.
>
> Sounds like, yeah.
>
>> There are instructions to convert endianess, see __bpf_prog_run(),
>> the ALU_END_TO_BE, ALU_END_TO_LE labels for details. There's a
>> BPF_ENDIAN() macro used in the test suite and other places.
>
> Ok, thanks! :)
>
> So sounds like I don't need anything special - should have a patch to
> hook up the wifi stuff soon.
Yeah, you shouldn't need anything special. In case the wifi progs have
their own BPF program type, I wouldn't even add it to may_access_skb()
to not further encourage LD_ABS/IND usage. F.e. lwt BPF programs are not
hooked up there either.
Thanks,
Daniel
next prev parent reply other threads:[~2017-04-11 11:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-11 10:38 eBPF - little-endian load instructions? Johannes Berg
2017-04-11 11:06 ` Daniel Borkmann
2017-04-11 11:15 ` Johannes Berg
2017-04-11 11:22 ` Daniel Borkmann [this message]
2017-04-11 11:26 ` Johannes Berg
2017-04-12 13:02 ` Johannes Berg
2017-04-12 16:58 ` Alexei Starovoitov
2017-04-12 19:38 ` Johannes Berg
2017-04-13 3:08 ` Alexei Starovoitov
2017-04-13 5:58 ` Johannes Berg
2017-04-14 18:42 ` Alexei Starovoitov
2017-04-15 7:06 ` Johannes Berg
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