linux-kernel - Re: BPF hash algo (Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in place of MD5)

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Date:   Thu, 22 Dec 2016 21:02:29 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Andy Lutomirski <luto@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Theodore Ts'o <tytso@....edu>, Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
Subject: Re: BPF hash algo (Re: [kernel-hardening] Re: [PATCH v7 3/6] random:
 use SipHash in place of MD5)

On 22.12.2016 20:56, Andy Lutomirski wrote:
> It's also not quite clear to me why userspace needs to be able to
> calculate the digest on its own.  A bpf(BPF_CALC_PROGRAM_DIGEST)
> command that takes a BPF program as input and hashes it would seem to
> serve the same purpose, and that would allow the kernel to key the
> digest and change the algorithm down the road without breaking things.

I think that people expect digests of BPF programs to be stable over
time and reboots.