From: Hannes Frederic Sowa <hannes@stressinduktion.org>
Subject: Re: BPF hash algo (Re: [kernel-hardening] Re: [PATCH v7 3/6] random:
 use SipHash in place of MD5)
Date: Thu, 22 Dec 2016 21:02:29 +0100
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Cc: Daniel Borkmann <daniel@iogearbox.net>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        "kernel-hardening@lists.openwall.com"
        <kernel-hardening@lists.openwall.com>,
        Theodore Ts'o <tytso@mit.edu>, Netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        David Laight <David.Laight@aculab.com>,
        Eric Dumazet <edumazet@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Eric Biggers <ebiggers3@gmail.com>,
        Tom Herbert <tom@herbertland.com>,
        Andi Kleen <ak@linux.intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
To: Andy Lutomirski <luto@kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>
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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.