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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB5F7C433F5 for ; Tue, 22 Feb 2022 07:47:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229744AbiBVHsS (ORCPT ); Tue, 22 Feb 2022 02:48:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58222 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229501AbiBVHsE (ORCPT ); Tue, 22 Feb 2022 02:48:04 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 226243968D for ; Mon, 21 Feb 2022 23:47:38 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id AD318212C5; Tue, 22 Feb 2022 07:47:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1645516056; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zqbKLfETHquQ//zH4sZBb/82594i7vrpZQI+kAgZZqo=; b=Ohsx3hUek/PGfa0AeORpHGURrKbjTevTEyxTe83vBBnN5JQxIft9Z0FTgbEQHc+XOeevQl APddYYsaRPnxB8nbR1jsqLlIDldZ6KEFSCbZDIexVwkp2QuNtNFjKf/w2tD559IcVYYyzU mJgnGqUTkxSliFbu/F3x7eI9mocqHn8= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 875C5A3B9A; Tue, 22 Feb 2022 07:47:36 +0000 (UTC) Date: Tue, 22 Feb 2022 08:47:36 +0100 From: Michal Hocko To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baolin Wang , Zhenguo Yao , Liu Yuntao , Dan Carpenter , Andrew Morton Subject: Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings Message-ID: References: <20220218212946.35441-1-mike.kravetz@oracle.com> <26565cd7-01b0-197c-6ce9-af92f5bc8563@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <26565cd7-01b0-197c-6ce9-af92f5bc8563@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 21-02-22 12:24:25, Mike Kravetz wrote: > On 2/21/22 00:42, Michal Hocko wrote: > > On Fri 18-02-22 13:29:46, Mike Kravetz wrote: > > [...] > >> @@ -4161,7 +4162,7 @@ static int __init hugepages_setup(char *s) > >> } > >> if (tmp >= nr_online_nodes) > >> goto invalid; > >> - node = tmp; > >> + node = array_index_nospec(tmp, nr_online_nodes); > >> p += count + 1; > >> /* Parse hugepages */ > >> if (sscanf(p, "%lu%n", &tmp, &count) != 1) > >> @@ -6889,9 +6890,9 @@ static int __init cmdline_parse_hugetlb_cma(char *p) > >> break; > >> > >> if (s[count] == ':') { > >> - nid = tmp; > >> - if (nid < 0 || nid >= MAX_NUMNODES) > >> + if (tmp >= MAX_NUMNODES) > >> break; > >> + nid = array_index_nospec(tmp, MAX_NUMNODES); > >> > >> s += count + 1; > >> tmp = memparse(s, &s); > > > > This is an early boot code, how is this supposed to be used as a side > > channel? > > I do not have an evil hacker mind, but I can not think of a way this one time > use of a user specified index could be an issue. It does add noise to the > BUILD REGRESSION emails sent to Andrew. Maybe Smack can be taught to ignore __init and other early boot functions. I do not have any strong objections to using array_index_nospec because it won't do any harm. Except that it makes a security measure a normal comodity so any future changes to array_index_nospec and its users will have to consult additional callers. Whether that is something we should deeply care about, I don't know. At minimum make sure to be explicit that this can hardly be a Spectre gadget as it is a _one_ time early boot call. If there is a scenario where this could be really abused then it should be mentioned explicitly. -- Michal Hocko SUSE Labs