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=-8.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED 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 A4146C282DE for ; Mon, 21 Jan 2019 07:38:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7336F20989 for ; Mon, 21 Jan 2019 07:38:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548056281; bh=XoWXVEff0N0Es0WH64+yM8SQAwzjbwWOP5nYX709aF4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=kAgldp+s/JnTsO5NOnR8nVZoY06hI0mSl9T/uciEjWice25h25Ov+buhRJMBf6cE9 Hqhfej5isYtNcksDdv92BZeMb7S2rhHguHDAsipjpMC9kJldzxoLGuaoLHTil8SF7+ gP388c3XGtH8nuaAH/AXqkReOQNR4n8arWI9rY20= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728562AbfAUHh7 (ORCPT ); Mon, 21 Jan 2019 02:37:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:54220 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725976AbfAUHh7 (ORCPT ); Mon, 21 Jan 2019 02:37:59 -0500 Received: from devbox (unknown [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6DFCC20855; Mon, 21 Jan 2019 03:57:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548043081; bh=XoWXVEff0N0Es0WH64+yM8SQAwzjbwWOP5nYX709aF4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=rgjZrhwdYbf86tjfRguycgCS1B3N3ws0/FPcPa2s6+Db2tSKPdU43erasTbtO5rM+ tQgKBLo9LTygz/+bEsflSYLu4ZDlrOf35/q7bk256IXxEsQEw8OEQVVNRipLj01sRW 2VFwjT0qcoH773Ljclu6wPtE5cPL6TzXe9DR3xM4= Date: Mon, 21 Jan 2019 12:57:56 +0900 From: Masami Hiramatsu To: Steven Rostedt , Srikar Dronamraju , Oleg Nesterov Cc: Elena Reshetova , peterz@infradead.org, mingo@redhat.com, akpm@linux-foundation.org, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, linux-kernel@vger.kernel.org, keescook@chromium.org, Masami Hiramatsu , Namhyung Kim Subject: Re: [PATCH] uprobes: convert uprobe.ref to refcount_t Message-Id: <20190121125756.b06de37c0c52b1b882b3df67@kernel.org> In-Reply-To: <20190116084452.773833d4@gandalf.local.home> References: <1547637627-29526-1-git-send-email-elena.reshetova@intel.com> <20190116084452.773833d4@gandalf.local.home> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 16 Jan 2019 08:44:52 -0500 Steven Rostedt wrote: > > [ Cc'ing Masami as he maintains uprobes (we need to add uprobes to > the MAINTAINERS file ] Thanks Steve, I think it is maintained mainly by Srikar and Oleg. Srikar, Oleg, could you update MAINTAINERS file to add UPROBES entry? And ack this change? Thank you, > > -- Steve > > On Wed, 16 Jan 2019 13:20:27 +0200 > Elena Reshetova wrote: > > > atomic_t variables are currently used to implement reference > > counters with the following properties: > > - counter is initialized to 1 using atomic_set() > > - a resource is freed upon counter reaching zero > > - once counter reaches zero, its further > > increments aren't allowed > > - counter schema uses basic atomic operations > > (set, inc, inc_not_zero, dec_and_test, etc.) > > > > Such atomic variables should be converted to a newly provided > > refcount_t type and API that prevents accidental counter overflows > > and underflows. This is important since overflows and underflows > > can lead to use-after-free situation and be exploitable. > > > > The variable uprobe.ref is used as pure reference counter. > > Convert it to refcount_t and fix up the operations. > > > > **Important note for maintainers: > > > > Some functions from refcount_t API defined in lib/refcount.c > > have different memory ordering guarantees than their atomic > > counterparts. > > The full comparison can be seen in > > https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon > > in state to be merged to the documentation tree. > > Normally the differences should not matter since refcount_t provides > > enough guarantees to satisfy the refcounting use cases, but in > > some rare cases it might matter. > > Please double check that you don't have some undocumented > > memory guarantees for this variable usage. > > > > For the uprobe.ref it might make a difference > > in following places: > > - put_uprobe(): decrement in refcount_dec_and_test() only > > provides RELEASE ordering and control dependency on success > > vs. fully ordered atomic counterpart > > > > Suggested-by: Kees Cook > > Reviewed-by: David Windsor > > Reviewed-by: Hans Liljestrand > > Signed-off-by: Elena Reshetova > > --- > > kernel/events/uprobes.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > index ad415f7..750aece 100644 > > --- a/kernel/events/uprobes.c > > +++ b/kernel/events/uprobes.c > > @@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem; > > > > struct uprobe { > > struct rb_node rb_node; /* node in the rb tree */ > > - atomic_t ref; > > + refcount_t ref; > > struct rw_semaphore register_rwsem; > > struct rw_semaphore consumer_rwsem; > > struct list_head pending_list; > > @@ -561,13 +561,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v > > > > static struct uprobe *get_uprobe(struct uprobe *uprobe) > > { > > - atomic_inc(&uprobe->ref); > > + refcount_inc(&uprobe->ref); > > return uprobe; > > } > > > > static void put_uprobe(struct uprobe *uprobe) > > { > > - if (atomic_dec_and_test(&uprobe->ref)) { > > + if (refcount_dec_and_test(&uprobe->ref)) { > > /* > > * If application munmap(exec_vma) before uprobe_unregister() > > * gets called, we don't get a chance to remove uprobe from > > @@ -658,7 +658,7 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe) > > rb_link_node(&uprobe->rb_node, parent, p); > > rb_insert_color(&uprobe->rb_node, &uprobes_tree); > > /* get access + creation ref */ > > - atomic_set(&uprobe->ref, 2); > > + refcount_set(&uprobe->ref, 2); > > > > return u; > > } > -- Masami Hiramatsu