[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Mon, 12 Dec 2016 22:57:14 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "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 v2] siphash: add cryptographically secure hashtable function
On Mon, Dec 12, 2016 at 10:44 PM, Jason A. Donenfeld <Jason@...c4.com> wrote:
> #if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
> switch (left) {
> case 0: break;
> case 1: b |= data[0]; break;
> case 2: b |= get_unaligned_le16(data); break;
> case 4: b |= get_unaligned_le32(data); break;
> default:
> b |= le64_to_cpu(load_unaligned_zeropad(data) &
> bytemask_from_count(left));
> break;
> }
> #else
> switch (left) {
> case 7: b |= ((u64)data[6]) << 48;
> case 6: b |= ((u64)data[5]) << 40;
> case 5: b |= ((u64)data[4]) << 32;
> case 4: b |= get_unaligned_le32(data); break;
> case 3: b |= ((u64)data[2]) << 16;
> case 2: b |= get_unaligned_le16(data); break;
> case 1: b |= data[0];
> }
> #endif
As it turns out, perhaps unsurprisingly, the code generation here is
really not nice, resulting in many branches instead of a computed
jump. I'll submit v3 with just a branch-less load_unaligned_zeropad
for the 64-bit/dcache case and the duff's device for the other case.
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
