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, URIBL_BLOCKED,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 8F593C10F0E for ; Mon, 15 Apr 2019 22:01:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DC3020880 for ; Mon, 15 Apr 2019 22:01:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="LhL8C6TG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726621AbfDOWB5 (ORCPT ); Mon, 15 Apr 2019 18:01:57 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:35496 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725804AbfDOWB5 (ORCPT ); Mon, 15 Apr 2019 18:01:57 -0400 Received: by mail-ed1-f68.google.com with SMTP id y67so2810027ede.2; Mon, 15 Apr 2019 15:01:55 -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=RJqS8aUhikcYPZrVt+ASSZGTsN7hObt7ZSRvFLdA9Mk=; b=LhL8C6TGF5qrwHscLfvYjjPlw4g5okjx2s5ZgM9HOzroeGIQMzvqhISoAfAYth10a2 dr9wc9VU21x4R/Nur2+AQsIHbTRTj9DyHAHnHdEM5p/ZImk4dw8/u7LYxGixa7s4qtLN iT6hxRE2b6PlL1q2AOYsT8W/FWqvIpz+LC6m6oNnx3nQdzES3CasL2gwnkFeP3nzdZ60 bYzCTuGQGH+q+bgkko+fEwlJPsJ2OxL0+TLNohlwvPgI311SMMRamCDAWYO4sv71FrNt jv5nWOABfUxIWUIyrj6IBbsyncnlSIQDabslysHhVtRyJrnPowjPn9gfPV5WfCUKUIRM tXRw== 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=RJqS8aUhikcYPZrVt+ASSZGTsN7hObt7ZSRvFLdA9Mk=; b=TrZv7vbSyBWfshD6sa0atW+frgPqP7kbQcCEms6u/gFHDsxktblwVmGvZ11igEthCt xbDuijs4u0I1OGS2LDiKbo77P2THwMRR/4eNJJ52KLHNQb6piHmM7a3vMoN79+3LHjIW DB5GPLPJOiESfhB1XcWyg6vkVIAiFqy1riGO7d4a5u4tAnShZWiyo83AfnaVEe0jbxYR OHId6VKj1qvpcLpQLqxloF7ClGJye8hzyW4+PNzS2Gd4gnMcGrxJV4cW2/2OEyTd1mXT 5hBNhNOnC+1mB1dTIK1OrZRwMyen3RYo7xqf+A1+oroOGG89ndMLcSzTfOUWbHR49eKQ B+bA== X-Gm-Message-State: APjAAAXrsDtremosMju0wDcHQVx6PU5AYq9PGGRbt4GCu1imntRWecwI URLk8+jqUOGNkMhB+3jfe20tM96IHNc= X-Google-Smtp-Source: APXvYqw7VZYDNV9MDxala6jKYeIHzOAnspA9bIpEKpijftLvnT4Wl6/M/VqXeJqHn+m7bFpZJD6xUQ== X-Received: by 2002:a50:b80e:: with SMTP id j14mr10773402ede.170.1555365714762; Mon, 15 Apr 2019 15:01:54 -0700 (PDT) Received: from archlinux-i9 ([2a01:4f9:2b:2b84::2]) by smtp.gmail.com with ESMTPSA id x13sm1862556eda.13.2019.04.15.15.01.53 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 15 Apr 2019 15:01:53 -0700 (PDT) Date: Mon, 15 Apr 2019 15:01:51 -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: <20190415220151.GA23056@archlinux-i9> References: <20190415183707.712011689@linuxfoundation.org> <20190415183729.170980546@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190415183729.170980546@linuxfoundation.org> 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 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. Nathan