netdev - Re: __sk_buff.data

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 20 Apr 2017 01:51:55 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Johannes Berg <johannes@...solutions.net>,
        Alexei Starovoitov <ast@...nel.org>
CC:     netdev <netdev@...r.kernel.org>
Subject: Re: __sk_buff.data_end

On 04/19/2017 11:31 PM, Johannes Berg wrote:
> Hi Alexei, Daniel,
>
> I'm looking at adding the __wifi_sk_buff I talked about, and I notice
> that it uses CB space to store data_end. Unfortunately, in a lot of
> cases, we don't have any CB space to spare in wifi.
>
> Is there any way to generate a series of instructions that instead does
> the necessary calculations? I don't actually *see* such a way, because
> I don't see how I could have a scratch register or scratch stack space,
> but perhaps there's a way to do it?

One option would be, similarly as in bpf_prog_run_save_cb(), to just
save / restore _only_ the data_end pointer portion for this. Calculating
this inline via bpf_convert_ctx_access() would indeed need one more
reg than just the dst reg available in order to perform the data_end
calculation only as BPF insns.