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=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 2C8E2C10F11 for ; Wed, 24 Apr 2019 17:35:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3BB921904 for ; Wed, 24 Apr 2019 17:35:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jne7BXuj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391912AbfDXRfb (ORCPT ); Wed, 24 Apr 2019 13:35:31 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:35736 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391874AbfDXRf0 (ORCPT ); Wed, 24 Apr 2019 13:35:26 -0400 Received: by mail-ed1-f65.google.com with SMTP id y67so16702895ede.2; Wed, 24 Apr 2019 10:35:24 -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=OhpoHmH9PcYpTjBCsGg1mfwgw+1CbGnmdprEyZaStxA=; b=jne7BXujXzAXTl3apOZxrfu6xC7HbjkZHCBjPNkQxYQ1ZGNa4cunDdfN6HOqWCXLhi XlROIYZfUHxV2U56KNSJXZovZ7bmCGRVM+IcWssvy/rEEdg/caovKcjEtS1GAzaMpsuH 8xtuT2x6SUVueeiF9Sp3Y31vyc+AB5YNQ2Zv8AVpfqL7QCiBXmU/sWELiRBaneS1qxC7 MN8ID/1KijEdvFeXsczyoPW2uDkSmejJ2GEFUI2nzb9onCpavxHeAMdazepSg9VehwCS 7PUed78S13Vijd89aZEZrf0T9G+7LvMI1CyPR9aYM5Vx6U52FdWIzbnf/KzV1gJTssxF EYlQ== 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=OhpoHmH9PcYpTjBCsGg1mfwgw+1CbGnmdprEyZaStxA=; b=XsDUa816dWKvfqU03Q1pJgtUM5PNaCzMGwoNQylLbHbugKLEmcWpWLeGzRtNrccGVk 2Zgm8Ydy1Lj+VDbnh/Lc2fq+Mjvv4McYsJU6CflAHYVWuzyBYsjhlQjycPZFZErcyKIl xdSFuuIQzvOBBev+dEo697smETCBTbijDkw2WjlQh+nd64wSKax9Bxw85/QBk6sKT++P 9CyY8ATPPwbREhZWzQZeHauZpT3hnMCN4Zyf//icPl69tyHYqsUIxXxJ5Y2EMiElqeNN me5HaJmkGw/6q+xFi15vDFINoNcEPHOZe9dxRlfL+FnLt7XHLOUgR0er4GRJkCBCF195 xkXQ== X-Gm-Message-State: APjAAAXHBelI2tBuokYyaBCm6lnV7ahFGuSjNrctE7ai2l017szqf2kY OBjBARrid0jppxdXnMKTe0k= X-Google-Smtp-Source: APXvYqyxZgZCAvraPT6EJp2RWAEwdu3e9Jp6ngThgUqfCvFMv+NsacHWaLM/xuQKyVOmhgJ9fgT3yw== X-Received: by 2002:a17:906:1249:: with SMTP id u9mr12568856eja.58.1556127323368; Wed, 24 Apr 2019 10:35:23 -0700 (PDT) Received: from archlinux-i9 ([2a01:4f9:2b:2b84::2]) by smtp.gmail.com with ESMTPSA id i41sm4003372ede.36.2019.04.24.10.35.22 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 24 Apr 2019 10:35:22 -0700 (PDT) Date: Wed, 24 Apr 2019 10:35:20 -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 3.18 055/104] arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value Message-ID: <20190424173520.GA13727@archlinux-i9> References: <20190424170839.996641496@linuxfoundation.org> <20190424170902.623665551@linuxfoundation.org> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="GvXjxJ+pjyke8COw" Content-Disposition: inline In-Reply-To: <20190424170902.623665551@linuxfoundation.org> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --GvXjxJ+pjyke8COw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hi Greg, On Wed, Apr 24, 2019 at 07:09:12PM +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 > @@ -26,8 +26,8 @@ > asm volatile( \ > "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" \ > @@ -50,7 +50,7 @@ futex_atomic_op_inuser(unsigned int enco > int cmp = (encoded_op >> 24) & 15; > int oparg = (int)(encoded_op << 8) >> 20; > int cmparg = (int)(encoded_op << 20) >> 20; > - int oldval = 0, ret, tmp; > + int oldval, ret, tmp; Please ensure the follow up fix gets queued up for 3.18 as well (backport attached). Thanks, Nathan > > if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) > oparg = 1U << (oparg & 0x1f); > @@ -62,23 +62,23 @@ futex_atomic_op_inuser(unsigned int enco > > 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: > > --GvXjxJ+pjyke8COw Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="0001-arm64-futex-Restore-oldval-initialization-to-work-ar.patch" >From 334d683655a0a4a68792ab1de6b20f4b559b0fcd Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Wed, 17 Apr 2019 00:21:21 -0700 Subject: [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers commit ff8acf929014b7f87315588e0daf8597c8aa9d1c upstream. Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") removed oldval's zero initialization in arch_futex_atomic_op_inuser because it is not necessary. Unfortunately, Android's arm64 GCC 4.9.4 [1] does not agree: ../kernel/futex.c: In function 'do_futex': ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized] return oldval == cmparg; ^ In file included from ../kernel/futex.c:73:0: ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here int oldval, ret, tmp; ^ GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser returns right away, avoiding the uninitialized use that it claims. Restoring the zero initialization works around this issue. [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/ Cc: stable@vger.kernel.org Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") Reviewed-by: Greg Kroah-Hartman Signed-off-by: Nathan Chancellor Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/futex.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h index 66bc1ef344f9..f7fda38d7183 100644 --- a/arch/arm64/include/asm/futex.h +++ b/arch/arm64/include/asm/futex.h @@ -50,7 +50,7 @@ futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr) int cmp = (encoded_op >> 24) & 15; int oparg = (int)(encoded_op << 8) >> 20; int cmparg = (int)(encoded_op << 20) >> 20; - int oldval, ret, tmp; + int oldval = 0, ret, tmp; if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) oparg = 1U << (oparg & 0x1f); -- 2.21.0 --GvXjxJ+pjyke8COw--