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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 E2B8BC47404 for ; Thu, 10 Oct 2019 02:25:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 682ED206C0 for ; Thu, 10 Oct 2019 02:25:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="ubZZhCQg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732659AbfJJCZJ (ORCPT ); Wed, 9 Oct 2019 22:25:09 -0400 Received: from conssluserg-05.nifty.com ([210.131.2.90]:32086 "EHLO conssluserg-05.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726370AbfJJCZI (ORCPT ); Wed, 9 Oct 2019 22:25:08 -0400 Received: from mail-vs1-f46.google.com (mail-vs1-f46.google.com [209.85.217.46]) (authenticated) by conssluserg-05.nifty.com with ESMTP id x9A2P043031114 for ; Thu, 10 Oct 2019 11:25:01 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-05.nifty.com x9A2P043031114 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1570674301; bh=uAYAlfm4I1nuexyDN7gOVUdZQWvIy84+ATaXpAvlJI4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=ubZZhCQga6eTUmSm6lVevSCPPlLS9xjbohJljRiDmwO5dXhugLcPuxtiMiIP2tz6n hy4NEAnJ9Sd1nT/2rRywjbA8tWpURZJFq96c61sWwnyA8Jwx0vzJP5f5B3sMjzPLwg TWURmkctSyinFGAiYbUmItws4+5ujpwbvkGX/HoHHCG6AfgU7e3tHCVzZAFTqB54zB z1rNtbvEL48VmxLrGLpiC4RBHu893Rd68IBdxHUF1BCA+JhvJYqVVs0iCYRGqYEIn7 2r1STnUpB/YoF13vhNFzN56QNFA034FuZLY53n9nnKWl8QU9noIlPF965w5aIvOCt6 tBnx9/yfRNOQQ== X-Nifty-SrcIP: [209.85.217.46] Received: by mail-vs1-f46.google.com with SMTP id w195so2862225vsw.11 for ; Wed, 09 Oct 2019 19:25:00 -0700 (PDT) X-Gm-Message-State: APjAAAUrXWn5lKPzVhdyEnLUZhvzEIz4FbBftDsrk0xbn3xaqczjhyb7 DyEl417WDUl6WYQT1vKVapzAo2sdy7oIXOFYClM= X-Google-Smtp-Source: APXvYqwssDuxB9ZpZp9504VgABsJ5XwuyUqMbmaC2qDT8E2b8FltAisFnRI5dPw1JVsHMKXVp22c9OlQChyZ/3eePN8= X-Received: by 2002:a67:ff14:: with SMTP id v20mr3832680vsp.215.1570674299760; Wed, 09 Oct 2019 19:24:59 -0700 (PDT) MIME-Version: 1.0 References: <20190811184938.1796-1-rikard.falkeborn@gmail.com> <20191009214502.637875-1-rikard.falkeborn@gmail.com> <20191009214502.637875-3-rikard.falkeborn@gmail.com> In-Reply-To: <20191009214502.637875-3-rikard.falkeborn@gmail.com> From: Masahiro Yamada Date: Thu, 10 Oct 2019 11:24:23 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [Patch v4 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs To: Rikard Falkeborn Cc: Andrew Morton , Borislav Petkov , Joe Perches , Johannes Berg , Kees Cook , Linux Kernel Mailing List , Ingo Molnar , Thomas Gleixner , Geert Uytterhoeven , Haren Myneni Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 10, 2019 at 6:45 AM Rikard Falkeborn wrote: > > GENMASK() and GENMASK_ULL() are supposed to be called with the high bit > as the first argument and the low bit as the second argument. Mixing > them will return a mask with zero bits set. > > Recent commits show getting this wrong is not uncommon, see e.g. > commit aa4c0c9091b0 ("net: stmmac: Fix misuses of GENMASK macro") and > commit 9bdd7bb3a844 ("clocksource/drivers/npcm: Fix misuse of GENMASK > macro"). > > To prevent such mistakes from appearing again, add compile time sanity > checking to the arguments of GENMASK() and GENMASK_ULL(). If both > arguments are known at compile time, and the low bit is higher than the > high bit, break the build to detect the mistake immediately. > > Since GENMASK() is used in declarations, BUILD_BUG_ON_ZERO() must be > used instead of BUILD_BUG_ON(). > > __builtin_constant_p does not evaluate is argument, it only checks if it > is a constant or not at compile time, and __builtin_choose_expr does not > evaluate the expression that is not chosen. Therefore, GENMASK(x++, 0) > does only evaluate x++ once. > > Commit 95b980d62d52 ("linux/bits.h: make BIT(), GENMASK(), and friends > available in assembly") made the macros in linux/bits.h available in > assembly. Since BUILD_BUG_OR_ZERO() is not asm compatible, disable the > checks if the file is included in an asm file. > > Due to bugs in GCC versions before 4.9 [0], disable the check if > building with a too old GCC compiler. > > [0]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449 > > Signed-off-by: Rikard Falkeborn Reviewed-by: Masahiro Yamada > --- > Geert, can you check if this works better? I do not have gcc 4.6-4.8 > readily installed. > > Kees, Masahiro, since I changed this patch, I didn't include your > reviewed-by tags. > > Changes in v4: > - Disable the argument check for GCC < 4.9 due to a compiler bug. > Changes in v3: > - Changed back to shorter macro argument names > - Remove casts and use 0 instead of UL(0) in GENMASK_INPUT_CHECK(), > since all results in GENMASK_INPUT_CHECK() are now ints. Update > commit message to reflect that. > > Changes in v2: > - Add comment about why inputs are not checked when used in asm file > - Use UL(0) instead of 0 > - Extract mask creation in a separate macro to improve readability > - Use high and low instead of h and l (part of this was extracted to a > separate patch) > - Updated commit message > > Joe Perches sent a series to fix the existing misuses of GENMASK(). > Those patches have been merged into Linus tree except two places where > the GENMASK misuse is in unused macros, which will not fail to build. > There was also a patch by Nathan Chancellor that have now been merged. > > include/linux/bits.h | 22 ++++++++++++++++++++-- > 1 file changed, 20 insertions(+), 2 deletions(-) > > diff --git a/include/linux/bits.h b/include/linux/bits.h > index 669d69441a62..f108302a3121 100644 > --- a/include/linux/bits.h > +++ b/include/linux/bits.h > @@ -18,12 +18,30 @@ > * position @h. For example > * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. > */ > -#define GENMASK(h, l) \ > +#if !defined(__ASSEMBLY__) && \ > + (!defined(CONFIG_CC_IS_GCC) || CONFIG_GCC_VERSION >= 49000) > +#include > +#define GENMASK_INPUT_CHECK(h, l) \ > + (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > + __builtin_constant_p((l) > (h)), (l) > (h), 0))) > +#else > +/* > + * BUILD_BUG_ON_ZERO is not available in h files included from asm files, > + * disable the input check if that is the case. > + */ > +#define GENMASK_INPUT_CHECK(h, l) 0 > +#endif > + > +#define __GENMASK(h, l) \ > (((~UL(0)) - (UL(1) << (l)) + 1) & \ > (~UL(0) >> (BITS_PER_LONG - 1 - (h)))) > +#define GENMASK(h, l) \ > + (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > > -#define GENMASK_ULL(h, l) \ > +#define __GENMASK_ULL(h, l) \ > (((~ULL(0)) - (ULL(1) << (l)) + 1) & \ > (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h)))) > +#define GENMASK_ULL(h, l) \ > + (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l)) > > #endif /* __LINUX_BITS_H */ > -- > 2.23.0 > -- Best Regards Masahiro Yamada