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=-5.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_MUTT 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 26146C10F13 for ; Tue, 16 Apr 2019 16:47:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE1DB206B6 for ; Tue, 16 Apr 2019 16:47:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="u3YzQ7Vj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728478AbfDPQr5 (ORCPT ); Tue, 16 Apr 2019 12:47:57 -0400 Received: from mail-ed1-f66.google.com ([209.85.208.66]:40386 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727180AbfDPQr5 (ORCPT ); Tue, 16 Apr 2019 12:47:57 -0400 Received: by mail-ed1-f66.google.com with SMTP id d46so13690580eda.7; Tue, 16 Apr 2019 09:47:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ZbeA4skiXNxO1iYF0snjEHkfBR0nml9mqhKeCLbw2NI=; b=u3YzQ7VjuUhA+ihj/tBV05JuV+DIrpX7tszf6cQQVUk1RCxWvxFzer4AyGTZMEyTER EzOM1qO4ce6h5NgbhyrwkI82YmV2ajU+M5UtmBTE97oX/O/xidof09knZMj7yUOR9uQx x4OdG/cYpKqTWYIQ5DMAdW78sYXJl45m2ZVsVjoDwmipDhPIpRcaQPZ0pwVr0XUYbFgw D11tA7GGUN0mNITUl36sCmUq0he0zyM63VbvYWYz2/7qH57eHit2bDXWiQrqJh3eR07P nVlW8C35EqroC2DuFnGnh17jLPwx3q5za42G1bdjQCHpt6ZYps173UQ/I1cepsutKWtZ TE6w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ZbeA4skiXNxO1iYF0snjEHkfBR0nml9mqhKeCLbw2NI=; b=Ld5IFkY66Rzdc8AkBhKtB6+0HkJpj2GkwOlgk3DZuAz2FMg0PdGgwnZvIPy1aZYo3A 3s0dMrJN8d3pXfm1mb4KhkMG8Z3BVMkJ92OsKO9IHsW2UeawNI9dtE/6gTeSHVu9sEo7 teff4goaNNBuiODjyEhK2LQGjq89neTKKKR4IkvjFZ6vEqQlL8dsTS2B8X9yvvLz7OmH 1UwyKOsTml+UBQZSI/z+RaUer/Rg+ESjMpGp5fCNp5KTTcKc5YS+FX5FfTxyODMoOY+a nMZDceM5pc8Irv6US8ZeUziojsOAnRW/HzD9EJDTe3ZlhfqWxRbzFmJyyThwuon9I1gU 4cyA== X-Gm-Message-State: APjAAAXYs+tbsgjd7vLP9cHEs+atI72c/kgFgAjy5R77Z1e9IoUr3Cd0 s8d9Dh1A3OfWPKZuLOgthGE= X-Google-Smtp-Source: APXvYqwXBz8b+g3OQY4ABMTSG8vvvO8CKGMQIZ7SC30Nl4v3l+igwznD1AsqsnLvmuO6NSW2npypsg== X-Received: by 2002:a50:b4c9:: with SMTP id x9mr51827673edd.132.1555433274278; Tue, 16 Apr 2019 09:47:54 -0700 (PDT) Received: from archlinux-i9 ([2a01:4f9:2b:2b84::2]) by smtp.gmail.com with ESMTPSA id j11sm7547256edk.9.2019.04.16.09.47.52 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 16 Apr 2019 09:47:53 -0700 (PDT) Date: Tue, 16 Apr 2019 09:47:51 -0700 From: Nathan Chancellor To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, stable@kernel.org, Will Deacon Subject: Re: [PATCH 4.9 72/76] arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value Message-ID: <20190416164751.GA25801@archlinux-i9> References: <20190415183707.712011689@linuxfoundation.org> <20190415183729.170980546@linuxfoundation.org> <20190415220151.GA23056@archlinux-i9> <20190416090052.GD4209@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190416090052.GD4209@kroah.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, Apr 16, 2019 at 11:00:52AM +0200, Greg Kroah-Hartman wrote: > On Mon, Apr 15, 2019 at 03:01:51PM -0700, Nathan Chancellor wrote: > > On Mon, Apr 15, 2019 at 08:44:36PM +0200, Greg Kroah-Hartman wrote: > > > From: Will Deacon > > > > > > commit 045afc24124d80c6998d9c770844c67912083506 upstream. > > > > > > Rather embarrassingly, our futex() FUTEX_WAKE_OP implementation doesn't > > > explicitly set the return value on the non-faulting path and instead > > > leaves it holding the result of the underlying atomic operation. This > > > means that any FUTEX_WAKE_OP atomic operation which computes a non-zero > > > value will be reported as having failed. Regrettably, I wrote the buggy > > > code back in 2011 and it was upstreamed as part of the initial arm64 > > > support in 2012. > > > > > > The reasons we appear to get away with this are: > > > > > > 1. FUTEX_WAKE_OP is rarely used and therefore doesn't appear to get > > > exercised by futex() test applications > > > > > > 2. If the result of the atomic operation is zero, the system call > > > behaves correctly > > > > > > 3. Prior to version 2.25, the only operation used by GLIBC set the > > > futex to zero, and therefore worked as expected. From 2.25 onwards, > > > FUTEX_WAKE_OP is not used by GLIBC at all. > > > > > > Fix the implementation by ensuring that the return value is either 0 > > > to indicate that the atomic operation completed successfully, or -EFAULT > > > if we encountered a fault when accessing the user mapping. > > > > > > Cc: > > > Fixes: 6170a97460db ("arm64: Atomic operations") > > > Signed-off-by: Will Deacon > > > Signed-off-by: Greg Kroah-Hartman > > > > > > --- > > > arch/arm64/include/asm/futex.h | 16 ++++++++-------- > > > 1 file changed, 8 insertions(+), 8 deletions(-) > > > > > > --- a/arch/arm64/include/asm/futex.h > > > +++ b/arch/arm64/include/asm/futex.h > > > @@ -33,8 +33,8 @@ > > > " prfm pstl1strm, %2\n" \ > > > "1: ldxr %w1, %2\n" \ > > > insn "\n" \ > > > -"2: stlxr %w3, %w0, %2\n" \ > > > -" cbnz %w3, 1b\n" \ > > > +"2: stlxr %w0, %w3, %2\n" \ > > > +" cbnz %w0, 1b\n" \ > > > " dmb ish\n" \ > > > "3:\n" \ > > > " .pushsection .fixup,\"ax\"\n" \ > > > @@ -53,29 +53,29 @@ > > > static inline int > > > arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr) > > > { > > > - int oldval = 0, ret, tmp; > > > + int oldval, ret, tmp; > > > > > > pagefault_disable(); > > > > > > switch (op) { > > > case FUTEX_OP_SET: > > > - __futex_atomic_op("mov %w0, %w4", > > > + __futex_atomic_op("mov %w3, %w4", > > > ret, oldval, uaddr, tmp, oparg); > > > break; > > > case FUTEX_OP_ADD: > > > - __futex_atomic_op("add %w0, %w1, %w4", > > > + __futex_atomic_op("add %w3, %w1, %w4", > > > ret, oldval, uaddr, tmp, oparg); > > > break; > > > case FUTEX_OP_OR: > > > - __futex_atomic_op("orr %w0, %w1, %w4", > > > + __futex_atomic_op("orr %w3, %w1, %w4", > > > ret, oldval, uaddr, tmp, oparg); > > > break; > > > case FUTEX_OP_ANDN: > > > - __futex_atomic_op("and %w0, %w1, %w4", > > > + __futex_atomic_op("and %w3, %w1, %w4", > > > ret, oldval, uaddr, tmp, ~oparg); > > > break; > > > case FUTEX_OP_XOR: > > > - __futex_atomic_op("eor %w0, %w1, %w4", > > > + __futex_atomic_op("eor %w3, %w1, %w4", > > > ret, oldval, uaddr, tmp, oparg); > > > break; > > > default: > > > > > > > > > > This causes a (false) build warning with AOSP's GCC 4.9.4 (which is > > used to build nearly all arm64 Android kernels before 4.14): > > > > CC kernel/futex.o > > ../kernel/futex.c: In function 'do_futex': > > ../kernel/futex.c:1492:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized] > > return oldval == cmparg; > > ^ > > In file included from ../kernel/futex.c:69:0: > > ../arch/arm64/include/asm/futex.h:56:6: note: 'oldval' was declared here > > int oldval, ret, tmp; > > ^ > > > > The only reason I bring this up is Qualcomm based kernels have a Python > > script that emulates -Werror, meaning this will be fatal for a large > > number of kernels, when this eventually gets merged into them. > > Argh, really? That's a buggy compiler that you have there, as oldval > will be set correctly if all is good, and if not, ret will be and the > code will error out. > Correct. > Working around broken compilers is not something I really like doing :( > Indeed, I wouldn't have brought it up if it wasn't the compiler for all Android 4.9 kernels aside from the Pixel 3 (XL). > That being said, does this also show up in the 4.19.y and 5.0.y tree > right now? If not, why not? > It does. $ make ARCH=arm64 CROSS_COMPILE=/bin/aarch64-linux-gnu- defconfig kernel/futex.o > thanks, > > greg k-h