From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C51AC1B0F2 for ; Wed, 20 Jun 2018 08:33:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 39F56208B0 for ; Wed, 20 Jun 2018 08:33:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 39F56208B0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=bootlin.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754198AbeFTIdb convert rfc822-to-8bit (ORCPT ); Wed, 20 Jun 2018 04:33:31 -0400 Received: from mail.bootlin.com ([62.4.15.54]:44107 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752750AbeFTId2 (ORCPT ); Wed, 20 Jun 2018 04:33:28 -0400 Received: by mail.bootlin.com (Postfix, from userid 110) id 9E1FD20750; Wed, 20 Jun 2018 09:38:15 +0200 (CEST) Received: from bbrezillon (AAubervilliers-681-1-50-153.w90-88.abo.wanadoo.fr [90.88.168.153]) by mail.bootlin.com (Postfix) with ESMTPSA id 4C29C203EC; Wed, 20 Jun 2018 09:38:05 +0200 (CEST) Date: Wed, 20 Jun 2018 09:38:05 +0200 From: Boris Brezillon To: Kees Cook Cc: Ivan Djelic , Brian Norris , David Woodhouse , Marek Vasut , Richard Weinberger , Linux mtd , LKML Subject: Re: [PATCH v3] lib/bch: Remove VLA usage Message-ID: <20180620093805.6d9c602e@bbrezillon> In-Reply-To: References: <20180531184525.GA11068@beast> <20180601110921.GC4695@parrot.com> X-Mailer: Claws Mail 3.15.0-dirty (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Kees, On Tue, 19 Jun 2018 16:48:17 -0700 Kees Cook wrote: > On Fri, Jun 1, 2018 at 4:09 AM, Ivan Djelic wrote: > > On Thu, May 31, 2018 at 11:45:25AM -0700, Kees Cook wrote: > >> In the quest to remove all stack VLA usage from the kernel[1], this > >> allocates a fixed size stack array to cover the range needed for > >> bch. This was done instead of a preallocation on the SLAB due to > >> performance reasons, shown by Ivan Djelic: > >> > >> little-endian, type sizes: int=4 long=8 longlong=8 > >> cpu: Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz > >> calibration: iter=4.9143µs niter=2034 nsamples=200 m=13 t=4 > >> > >> Buffer allocation | Encoding throughput (Mbit/s) > >> --------------------------------------------------- > >> on-stack, VLA | 3988 > >> on-stack, fixed | 4494 > >> kmalloc | 1967 > >> > >> So this change actually improves performance too, it seems. > >> > >> The resulting stack allocation can get rather large; without > >> CONFIG_BCH_CONST_PARAMS, it will allocate 4096 bytes, which > >> trips the stack size checking: > >> > >> lib/bch.c: In function ‘encode_bch’: > >> lib/bch.c:261:1: warning: the frame size of 4432 bytes is larger than 2048 bytes [-Wframe-larger-than=] > >> > >> Even the default case for "allmodconfig" (with CONFIG_BCH_CONST_M=14 and > >> CONFIG_BCH_CONST_T=4) would have started throwing a warning: > >> > >> lib/bch.c: In function ‘encode_bch’: > >> lib/bch.c:261:1: warning: the frame size of 2288 bytes is larger than 2048 bytes [-Wframe-larger-than=] > >> > >> But this is how large it's always been; it was just hidden from > >> the checker because it was a VLA. So the Makefile has been adjusted to > >> silence this warning for anything smaller than 4500 bytes, which should > >> provide room for normal cases, but still low enough to catch any future > >> pathological situations. > >> > >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com > >> > >> Signed-off-by: Kees Cook > >> --- > >> v3: fix r_bytes to whole-word size > >> v2: switch to fixed-size stack array > >> --- > >> lib/Makefile | 1 + > >> lib/bch.c | 23 +++++++++++++++-------- > >> 2 files changed, 16 insertions(+), 8 deletions(-) > > > > > > The patch looks good to me. It also passed my regression tests. > > > > Reviewed-by: Ivan Djelic > > Tested-by: Ivan Djelic > > Thanks for the review and testing! > > Who's the best person to carry this patch? Looks like all users of this lib are in drivers/mtd, so I can take the patches if you want, but I can also let you take them if you prefer. Here is my Acked-by: Boris Brezillon in case you were waiting for it. Regards, Boris