linux-kernel - Re: [PATCH v3] siphash: add cryptographically secure hashtable function

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Message-ID: <CAHmME9rViJoDbJ_30ocqHEFESjeLMZOerjbnXmhQ4P32pbXRFg@mail.gmail.com>
Date:   Tue, 13 Dec 2016 23:43:06 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        George Spelvin <linux@...izon.com>,
        Scott Bauer <sbauer@....utah.edu>,
        Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        "Daniel J . Bernstein" <djb@...yp.to>
Subject: Re: [PATCH v3] siphash: add cryptographically secure hashtable function

Hi Eric,

On Tue, Dec 13, 2016 at 9:39 AM, Eric Biggers <ebiggers3@...il.com> wrote:
> Hmm, I don't think you can really do load_unaligned_zeropad() without first
> checking for 'left != 0'.  The fixup section for load_unaligned_zeropad()
> assumes that rounding the pointer down to a word boundary will produce an
> address from which an 'unsigned long' can be loaded.  But if 'left = 0' and we
> happen to be on a page boundary with the next page unmapped, then this will not
> be true and the second load will still fault.

Excellent point. I haven't been able to trigger this in my
experiments, but it doesn't look like there's much to prevent this
from happening. I'll submit a v4 with this as fixed, since there
hasn't been any other code quality issues.

Jason