linux-kernel - Re: [PATCH 0/3] add %pX specifier

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Date:   Wed, 11 Oct 2017 14:29:09 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     "Tobin C. Harding" <me@...in.cc>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        KVM list <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ker.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>
Subject: Re: [PATCH 0/3] add %pX specifier

On Wed, Oct 11, 2017 at 1:11 PM, Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Indeed the correct functions to use would be siphash_1u32 or
> siphash_1u64, depending. Depending on the popularity of that, we might
> even consider making a siphash_1ulong helper, I suppose.

Yeah, siphash is probably the sanest thing to use.

How bad would it be to use HalfSipHash on 32-bit architectures?

On a 32-bit machine, the full siphash is pretty expensive - big
constants, and lots of 64-bit shifts. And 32-bit machines also tend to
mean "slow machines" these days.

I suspect there's little point in worrying a ton about the 64-bit key,
considering that I think the *input* is generally more guessable than
the output or the key.

           Linus