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=-19.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 1519CC432C3 for ; Tue, 3 Dec 2019 11:28:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BC38520675 for ; Tue, 3 Dec 2019 11:28:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="TkqU1bgH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BC38520675 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 551306B049E; Tue, 3 Dec 2019 06:28:04 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 527B56B04AD; Tue, 3 Dec 2019 06:28:04 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 43E016B04AE; Tue, 3 Dec 2019 06:28:04 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0003.hostedemail.com [216.40.44.3]) by kanga.kvack.org (Postfix) with ESMTP id 2F4356B049E for ; Tue, 3 Dec 2019 06:28:04 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id DE4122473 for ; Tue, 3 Dec 2019 11:28:03 +0000 (UTC) X-FDA: 76223606046.08.drug25_464d08f1b0524 X-HE-Tag: drug25_464d08f1b0524 X-Filterd-Recvd-Size: 8731 Received: from mail-wm1-f66.google.com (mail-wm1-f66.google.com [209.85.128.66]) by imf49.hostedemail.com (Postfix) with ESMTP for ; Tue, 3 Dec 2019 11:28:02 +0000 (UTC) Received: by mail-wm1-f66.google.com with SMTP id p17so3035041wmi.3 for ; Tue, 03 Dec 2019 03:28:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=dJIeUwIGkKfd5G6Dn+RjqiwNFQhIAfQfW+Oe2wdQ7qI=; b=TkqU1bgH+jJ4P1qVGchLQ+wibSsM6CtIf33Q9qZpbwVMQ64iebywSlzhLX8NptOh+1 K8ARwPylJOX+NRUrnzGzdhYwHB+dvkxKToChMNBS5ufWqNc3NZC2l/a4mWByWU11IH9l r4TVUoslBWxXFkewbqpLOvjsPewuvofElBVlRWTMH9hzCCgfIUTcQ1u1YxnurmZfdWDB 8l/qr5mxNzWEfYllDfVAdsqpBB7MmQBDOa1DyhA50+pUemAV/CoAxEAAnqyVn9PiNpgG xO9iK4LDadA/YAzpvxpPfw9/aC/tJEZgaz8uk6dQvunc2uNE5DXWKTWqspvGWbhUiK0D OYEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=dJIeUwIGkKfd5G6Dn+RjqiwNFQhIAfQfW+Oe2wdQ7qI=; b=iDTvUwF13WezTcCkfik+mTaFuz2EBtAW3i8vD7fzPlboJAt4XZ79KOx+y6XDvIgZAK ta1MQ1k9cHD0wFm1ikaxVFmBJ8GxywVoiRLDFIvSV5ymYEC2FptM0PUyXUnZ4XwG5K2H 0dX+82Rk3nwk1vSYRhJoG6um7JXdB5bjIj8OhevevmvAU6NqR6uXRibvSLAuvwS1a1RZ JaQyVsg4csR+XRipgG5yNsCwdJ1knx5pmha4EhLJyyDf/1lraIMEHsANHjUcCclR4VIk oH5xI75eqX272jePQ83jtfJhv9i7VsBVooAIfghD7seaMqByrHLLbMDHS9+QfHuvH++A zl9w== X-Gm-Message-State: APjAAAUnL93yvLscdR5g2xfrRyJe5i1lnsjCK6jlyvPOtJ1xQKo3jApd AmQ32vuBudbq9npYQYuAf2NVGEB3ppYL9DFMXbSGUA== X-Google-Smtp-Source: APXvYqwUI8YrCgueIhjpK3Obmx+imlqQVyq0ohNwGXCRwwMLHm+IE5pvmhLoQ9tv3IA+brbxyRRA7FdCKFjItu9iBpQ= X-Received: by 2002:a05:600c:1:: with SMTP id g1mr33916156wmc.131.1575372481401; Tue, 03 Dec 2019 03:28:01 -0800 (PST) MIME-Version: 1.0 References: <20191122112621.204798-1-glider@google.com> <20191122112621.204798-32-glider@google.com> In-Reply-To: From: Alexander Potapenko Date: Tue, 3 Dec 2019 12:27:50 +0100 Message-ID: Subject: Re: [PATCH RFC v3 31/36] kmsan: disable strscpy() optimization under KMSAN To: Marco Elver Cc: Vegard Nossum , Dmitry Vyukov , Linux Memory Management List , Al Viro , Andreas Dilger , Andrew Morton , Andrey Konovalov , Andrey Ryabinin , Andy Lutomirski , Ard Biesheuvel , Arnd Bergmann , Christoph Hellwig , Christoph Hellwig , "Darrick J. Wong" , "David S. Miller" , Dmitry Torokhov , Eric Biggers , Eric Dumazet , Eric Van Hensbergen , Greg Kroah-Hartman , Harry Wentland , Herbert Xu , Ilya Leoshkevich , Ingo Molnar , Jason Wang , Jens Axboe , Marek Szyprowski , Mark Rutland , "Martin K. Petersen" , Martin Schwidefsky , Matthew Wilcox , "Michael S. Tsirkin" , Michal Simek , Petr Mladek , Qian Cai , Randy Dunlap , Robin Murphy , Sergey Senozhatsky , Steven Rostedt , Takashi Iwai , "Theodore Ts'o" , Thomas Gleixner , Vasily Gorbik , Wolfram Sang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Dec 3, 2019 at 12:25 PM Marco Elver wrote: > > On Tue, 3 Dec 2019 at 12:19, Alexander Potapenko wrot= e: > > > > On Mon, Dec 2, 2019 at 5:23 PM Alexander Potapenko = wrote: > > > > > > On Mon, Dec 2, 2019 at 4:51 PM Marco Elver wrote: > > > > > > > > On Fri, 22 Nov 2019 at 12:28, wrote: > > > > > > > > > > Disable the efficient 8-byte reading under KMSAN to avoid false p= ositives. > > > > > > > > > > Signed-off-by: Alexander Potapenko > > > > > To: Alexander Potapenko > > > > > Cc: Vegard Nossum > > > > > Cc: Dmitry Vyukov > > > > > Cc: linux-mm@kvack.org > > > > > > > > > > --- > > > > > > > > > > Change-Id: I25d1acf5c3df6eff85894cd94f5ddbe93308271c > > > > > --- > > > > > lib/string.c | 5 ++++- > > > > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/lib/string.c b/lib/string.c > > > > > index 08ec58cc673b..15efdc51bda6 100644 > > > > > --- a/lib/string.c > > > > > +++ b/lib/string.c > > > > > @@ -186,7 +186,10 @@ ssize_t strscpy(char *dest, const char *src,= size_t count) > > > > > if (count =3D=3D 0 || WARN_ON_ONCE(count > INT_MAX)) > > > > > return -E2BIG; > > > > > > > > > > -#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > > > > > +/** > > > > > > > > Why a doc comment? > > > Will fix, thanks! > > > > > + * Disable the efficient 8-byte reading under KMSAN to avoid fal= se positives. > > > > > + */ > > > > > > > > AFAIK the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS case is about > > > > unaligned accesses crossing page boundaries. In the #else case it's > > > > still going to do word-at-a-time if both src and dest are aligned, = so > > > > the comment above is somewhat inaccurate. > > > Yes, this makes little sense. > > > Reading word-at-a-time shouldn't induce any errors, although it may > > > generate redundant stack IDs for values that will never be used. > > > I'll try to drop this patch. > > Turns out the patch is still needed, as read_word_at_a_time may read > > uninitialized bytes which are then used in comparisons. > > I've changed the patch to always set max=3D0 under KMSAN: > > https://github.com/google/kmsan/commit/3ff43863bf53dd871a3d4dc4fbb2a76d= 79b4db4f > > Will include this version in v4 series. > > So was the previous version working because all strscpy where this was > relevant were unaligned? Right. > Re new patch: I think here it should be trivial to use 'if > (IS_ENABLED(CONFIG_KMSAN))' instead of #ifdef. Yes, sorry, I always forget about IS_ENABLED. > Thanks, > -- Marco > > > > > > +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && !defined(= CONFIG_KMSAN) > > > > > /* > > > > > * If src is unaligned, don't cross a page boundary, > > > > > * since we don't know if the next page is mapped. > > > > > -- > > > > > 2.24.0.432.g9d3f5f5b63-goog > > > > > > > > > > > > > > > > > -- > > > Alexander Potapenko > > > Software Engineer > > > > > > Google Germany GmbH > > > Erika-Mann-Stra=C3=9Fe, 33 > > > 80636 M=C3=BCnchen > > > > > > Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Halimah DeLaine Prado > > > Registergericht und -nummer: Hamburg, HRB 86891 > > > Sitz der Gesellschaft: Hamburg > > > > > > > > -- > > Alexander Potapenko > > Software Engineer > > > > Google Germany GmbH > > Erika-Mann-Stra=C3=9Fe, 33 > > 80636 M=C3=BCnchen > > > > Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Halimah DeLaine Prado > > Registergericht und -nummer: Hamburg, HRB 86891 > > Sitz der Gesellschaft: Hamburg --=20 Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Stra=C3=9Fe, 33 80636 M=C3=BCnchen Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg