linux-kernel - Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF

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Message-Id: <1481922923.2204853.821591377.2CD623CB@webmail.messagingengine.com>
Date:   Fri, 16 Dec 2016 22:15:23 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        kernel-hardening@...ts.openwall.com,
        "Theodore Ts'o" <tytso@....edu>,
        George Spelvin <linux@...encehorizons.net>,
        Andi Kleen <ak@...ux.intel.com>,
        David Miller <davem@...emloft.net>,
        David Laight <David.Laight@...lab.com>,
        "Daniel J . Bernstein" <djb@...yp.to>,
        Eric Biggers <ebiggers3@...il.com>,
        "Jean-Philippe Aumasson" <jeanphilippe.aumasson@...il.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Netdev <netdev@...r.kernel.org>,
        Tom Herbert <tom@...bertland.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add cryptographically
 secure PRF

On Fri, Dec 16, 2016, at 22:01, Jason A. Donenfeld wrote:
> Yes, on x86-64. But on i386 chacha20 incurs nearly the same kind of
> slowdown as siphash, so I expect the comparison to be more or less
> equal. There's another thing I really didn't like about your chacha20
> approach which is that it uses the /dev/urandom pool, which means
> various things need to kick in in the background to refill this.
> Additionally, having to refill the buffered chacha output every 32 or
> so longs isn't nice. These things together make for inconsistent and
> hard to understand general operating system performance, because
> get_random_long is called at every process startup for ASLR. So, in
> the end, I believe there's another reason for going with the siphash
> approach: deterministic performance.

*Hust*, so from where do you generate your key for siphash if called
early from ASLR?

Bye,
Hannes