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,URIBL_BLOCKED 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 71C3FC43142 for ; Sun, 24 Jun 2018 20:13:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2717425300 for ; Sun, 24 Jun 2018 20:13:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2717425300 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 S1751745AbeFXUNC convert rfc822-to-8bit (ORCPT ); Sun, 24 Jun 2018 16:13:02 -0400 Received: from mail.bootlin.com ([62.4.15.54]:57975 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750972AbeFXUNB (ORCPT ); Sun, 24 Jun 2018 16:13:01 -0400 Received: by mail.bootlin.com (Postfix, from userid 110) id 2EA142079C; Sun, 24 Jun 2018 22:12:59 +0200 (CEST) Received: from bbrezillon (unknown [91.160.177.164]) by mail.bootlin.com (Postfix) with ESMTPSA id DD023206A0; Sun, 24 Jun 2018 22:12:58 +0200 (CEST) Date: Sun, 24 Jun 2018 22:12:59 +0200 From: Boris Brezillon To: Kees Cook Cc: Richard Weinberger , LKML , Marek Vasut , Linux mtd , Ivan Djelic , Brian Norris , David Woodhouse Subject: Re: [PATCH v3] lib/bch: Remove VLA usage Message-ID: <20180624221259.3c39c77e@bbrezillon> In-Reply-To: References: <20180531184525.GA11068@beast> <20180601110921.GC4695@parrot.com> <20180620093805.6d9c602e@bbrezillon> 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 On Wed, 20 Jun 2018 11:16:11 -0700 Kees Cook wrote: > On Wed, Jun 20, 2018 at 12:38 AM, Boris Brezillon > wrote: > > 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. > > I'd love it if you could take it; thank you! Applied to mtd/next. Thanks, Boris