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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 0BDE0C43441 for ; Thu, 22 Nov 2018 16:19:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5A3420672 for ; Thu, 22 Nov 2018 16:19:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5A3420672 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405930AbeKWC7t (ORCPT ); Thu, 22 Nov 2018 21:59:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38748 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730352AbeKWC7s (ORCPT ); Thu, 22 Nov 2018 21:59:48 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DEE6931256C9; Thu, 22 Nov 2018 16:19:45 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.142]) by smtp.corp.redhat.com (Postfix) with SMTP id 3DF485C21E; Thu, 22 Nov 2018 16:19:43 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 22 Nov 2018 17:19:45 +0100 (CET) Date: Thu, 22 Nov 2018 17:19:42 +0100 From: Oleg Nesterov To: Andrea Parri Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , stable@kernel.org Subject: Re: [PATCH] uprobes: Fix handle_swbp() vs. unregister() + register() race once more Message-ID: <20181122161942.GG28270@redhat.com> References: <20181122161031.15179-1-andrea.parri@amarulasolutions.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181122161031.15179-1-andrea.parri@amarulasolutions.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Thu, 22 Nov 2018 16:19:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/22, Andrea Parri wrote: > > Commit 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + > register() race") added the UPROBE_COPY_INSN flag, and corresponding > smp_wmb() and smp_rmb() memory barriers, to ensure that handle_swbp() > uses fully-initialized uprobes only. > > However, the smp_rmb() is mis-placed: this barrier should be placed > after handle_swbp() has tested for the flag, thus guaranteeing that > (program-order) subsequent loads from the uprobe can see the initial > stores performed by prepare_uprobe(). > > Move the smp_rmb() accordingly. Also amend the comments associated > to the two memory barriers to indicate their actual locations. > > Signed-off-by: Andrea Parri > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Arnaldo Carvalho de Melo > Cc: Alexander Shishkin > Cc: Jiri Olsa > Cc: Namhyung Kim > Cc: Oleg Nesterov > Cc: stable@kernel.org > Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race") Thanks, Acked-by: Oleg Nesterov > --- > kernel/events/uprobes.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 96d4bee83489b..322e97bbb4370 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -829,7 +829,7 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file, > BUG_ON((uprobe->offset & ~PAGE_MASK) + > UPROBE_SWBP_INSN_SIZE > PAGE_SIZE); > > - smp_wmb(); /* pairs with rmb() in find_active_uprobe() */ > + smp_wmb(); /* pairs with the smp_rmb() in handle_swbp() */ > set_bit(UPROBE_COPY_INSN, &uprobe->flags); > > out: > @@ -2178,10 +2178,18 @@ static void handle_swbp(struct pt_regs *regs) > * After we hit the bp, _unregister + _register can install the > * new and not-yet-analyzed uprobe at the same address, restart. > */ > - smp_rmb(); /* pairs with wmb() in install_breakpoint() */ > if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags))) > goto out; > > + /* > + * Pairs with the smp_wmb() in prepare_uprobe(). > + * > + * Guarantees that if we see the UPROBE_COPY_INSN bit set, then > + * we must also see the stores to &uprobe->arch performed by the > + * prepare_uprobe() call. > + */ > + smp_rmb(); > + > /* Tracing handlers use ->utask to communicate with fetch methods */ > if (!get_utask()) > goto out; > -- > 2.17.1 >