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 56D4FC433EF for ; Wed, 23 Feb 2022 08:35:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238989AbiBWIgO (ORCPT ); Wed, 23 Feb 2022 03:36:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233549AbiBWIgM (ORCPT ); Wed, 23 Feb 2022 03:36:12 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 511116B084 for ; Wed, 23 Feb 2022 00:35:45 -0800 (PST) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id EF53C21138; Wed, 23 Feb 2022 08:35:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1645605343; 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=02cl20i2Gq77a/yxNfOu7oH0En+DuGmAqR7Fchia8K0=; b=UzvwPXkBd9GmrXx/Os/RtO2ydkyecHnJjjKFIucWXNY6ETW01xsThg3eHy0msviPF3aR5D eg+jkY3WePRE4zvxvtOfACRlph9JnzkS0/7zkidwE3BP8x513apnBzIpDMmdzbikRHUiQb N7IEkNCLlAqd84+mqfIgEujKsDkATNE= 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 AEC6FA3B81; Wed, 23 Feb 2022 08:35:43 +0000 (UTC) Date: Wed, 23 Feb 2022 09:35:43 +0100 From: Michal Hocko To: Dan Carpenter Cc: "Schaufler, Casey" , Mike Kravetz , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Baolin Wang , Zhenguo Yao , Liu Yuntao , Andrew Morton , "casey@schaufler-ca.com" 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> <20220222163610.GG3943@kadam> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220222163610.GG3943@kadam> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 22-02-22 19:36:10, Dan Carpenter wrote: > On Tue, Feb 22, 2022 at 04:15:45PM +0000, Schaufler, Casey wrote: > > > -----Original Message----- > > > From: Michal Hocko > > > Sent: Monday, February 21, 2022 11:48 PM > > > To: Mike Kravetz > > > Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; Baolin Wang > > > ; Zhenguo Yao > > > ; Liu Yuntao ; Dan > > > Carpenter ; Andrew Morton > > foundation.org> > > > Subject: Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings > > > > > > 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. > > > > Why is Smack getting called out? The relationship is not obvious. > > > > He meant Smatch. It's a really common mistake that I did not anticipate > in 2002. Right. My bad. > I can probably silence the spectre warnings for __init functions. TBH, > I don't really understand spectre at all so I mostly ignore those > warnings. :/ AFAIU the spectre gadget would need to be called repeatedly to be usable for a side channel attack. I might be really missing some scenario but to me it seems that __init functions cannot really be used for that. -- Michal Hocko SUSE Labs