netdev - Re: [DRAFT PATCH] random32: make prandom

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Date:   Fri, 14 Aug 2020 17:32:32 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Willy Tarreau <w@....eu>
Cc:     George Spelvin <lkml@....org>, Amit Klein <aksecurity@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        netdev@...r.kernel.org
Subject: Re: [DRAFT PATCH] random32: make prandom_u32() output unpredictable

On Thu, Aug 13, 2020 at 10:06 AM Willy Tarreau <w@....eu> wrote:
>
> On Thu, Aug 13, 2020 at 09:53:11AM +0200, Sedat Dilek wrote:
> > On Wed, Aug 12, 2020 at 5:21 AM Willy Tarreau <w@....eu> wrote:
> > >
> > > On Tue, Aug 11, 2020 at 12:51:43PM +0200, Sedat Dilek wrote:
> > > > Can you share this "rebased to mainline" version of George's patch?
> > >
> > > You can pick it from there if that helps, but keep in mind that
> > > it's just experimental code that we use to explain our ideas and
> > > that we really don't care a single second what kernel it's applied
> > > to:
> > >
> > >    https://git.kernel.org/pub/scm/linux/kernel/git/wtarreau/cleanups.git/log/?h=20200811-prandom-1
> > >
> >
> > Thanks Willy.
> >
> > I disagree: the base for testing should be clear(ly communicated).
>
> It is. As you can see on the log above, this was applied on top of
> fc80c51fd4b2, there's nothing special here. In addition we're not even
> talking about testing nor calling for testers, just trying to find a
> reasonable solution. Maybe today I'll be able to re-run a few tests by
> the way.
>
> > There are two diffs from Eric to #1: add a trace event for
> > prandom_u32() and #2: a removal of prandom_u32() call in
> > tcp_conn_request().
> > In case you have not seen.
>
> I've seen, just not had the time to test yet.
>

Now with Eric' patch (see [1]) in mainline...

commit 94c7eb54c4b8e81618ec79f414fe1ca5767f9720
"random32: add a tracepoint for prandom_u32()"

...I gave Willy's patches a try and used the Linux Test Project (LTP)
for testing.

[ PERF SESSION #2 ]

Link: https://github.com/linux-test-project/ltp/blob/master/doc/mini-howto-building-ltp-from-git.txt

cd /opt/ltp

/home/dileks/bin/perf record -a -g -e random:prandom_u32 ./runltp -f
net.features -s tcp_fastopen

/home/dileks/bin/perf report --no-children --stdio > ./perf-report.txt
/home/dileks/bin/perf script > ./perf-script.txt

du -h perf*
34M     perf.data
20K     perf-report.txt
134M    perf-script.txt

Note: For a first test I used net.features::tcp_fastopen.

Attached is my perf-report.txt.

- Sedat -

[1] https://git.kernel.org/linus/94c7eb54c4b8e81618ec79f414fe1ca5767f9720

View attachment "perf-report.txt" of type "text/plain" (20177 bytes)