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=-12.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 530E3C433E0 for ; Tue, 9 Feb 2021 14:22:12 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E43F664E4F for ; Tue, 9 Feb 2021 14:22:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E43F664E4F Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.83267.154494 (Exim 4.92) (envelope-from ) id 1l9Ttt-0000p7-27; Tue, 09 Feb 2021 14:21:57 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 83267.154494; Tue, 09 Feb 2021 14:21:57 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l9Tts-0000p0-TB; Tue, 09 Feb 2021 14:21:56 +0000 Received: by outflank-mailman (input) for mailman id 83267; Tue, 09 Feb 2021 14:21:56 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l9Tts-0000ov-C0 for xen-devel@lists.xenproject.org; Tue, 09 Feb 2021 14:21:56 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id d1a553e2-f37c-4660-9402-b38d3034adc0; Tue, 09 Feb 2021 14:21:55 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 1B0AFAD6A; Tue, 9 Feb 2021 14:21:54 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d1a553e2-f37c-4660-9402-b38d3034adc0 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1612880514; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=mIQB3lHLlmRhkVMcXJDBArQs4ArE4UWm4/bPgZ6ct9A=; b=Yq1vrBGj7DGnnkuAVbyaw2O4Ws/sJE7DJZq0pEBEMipj9uMSzKhHFoD1Aeo/SDBaSQF7w0 3RS6l6spLAtasQLLNAnuZ0aQYzJ4sJSlcLLnwDhkMyNmF534UFlQrDSEIQ7tiGfGL+Q1tu y5MCn3EEGBpoTaRWLO/FYRceyUJ7xwU= Subject: Re: [PATCH HVM v2 1/1] hvm: refactor set param To: Norbert Manthey Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , Ian Jackson , xen-devel@lists.xenproject.org References: <20210205203905.8824-1-nmanthey@amazon.de> <9f753ee9-73c5-aa2c-3c68-eed7e0c2608b@amazon.de> From: Jan Beulich Message-ID: <1a50a8c3-44f5-9ea9-7ff1-0d716bc05ebd@suse.com> Date: Tue, 9 Feb 2021 15:21:54 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 09.02.2021 14:56, Norbert Manthey wrote: > On 2/9/21 2:45 PM, Jan Beulich wrote: >> On 09.02.2021 14:41, Norbert Manthey wrote: >>> On 2/9/21 10:40 AM, Jan Beulich wrote: >>>> On 08.02.2021 20:47, Norbert Manthey wrote: >>>>> On 2/8/21 3:21 PM, Jan Beulich wrote: >>>>>> On 05.02.2021 21:39, Norbert Manthey wrote: >>>>>>> @@ -4108,6 +4108,13 @@ static int hvm_allow_set_param(struct domain *d, >>>>>>> if ( rc ) >>>>>>> return rc; >>>>>>> >>>>>>> + if ( index >= HVM_NR_PARAMS ) >>>>>>> + return -EINVAL; >>>>>>> + >>>>>>> + /* Make sure we evaluate permissions before loading data of domains. */ >>>>>>> + block_speculation(); >>>>>>> + >>>>>>> + value = d->arch.hvm.params[index]; >>>>>>> switch ( index ) >>>>>>> { >>>>>>> /* The following parameters should only be changed once. */ >>>>>> I don't see the need for the heavier block_speculation() here; >>>>>> afaict array_access_nospec() should do fine. The switch() in >>>>>> context above as well as the switch() further down in the >>>>>> function don't have any speculation susceptible code. >>>>> The reason to block speculation instead of just using the hardened index >>>>> access is to not allow to speculatively load data from another domain. >>>> Okay, looks like I got mislead by the added bounds check. Why >>>> do you add that, when the sole caller already has one? It'll >>>> suffice since you move the array access past the barrier, >>>> won't it? >>> I can drop that bound check again. This was added to make sure other >>> callers would be save as well. Thinking about this a little more, the >>> check could actually be moved into the hvm_allow_set_param function, >>> above the first index access in that function. Are there good reasons to >>> not move the index check into the allow function? >> I guess I'm confused: We're talking about dropping the check >> you add to hvm_allow_set_param() and you suggest to "move" it >> right there? > > Yes. I can either just no introduce that check in that function (which > is what you suggested). As an alternative, to have all checks in one > function, I proposed to instead move it into hvm_allow_set_param. Oh, I see. What I'd like to be the result of your re-arrangement is symmetry between "get" and "set" where possible in this regard, and asymmetry having a clear reason. Seeing that hvm_{get,set}_param() are the non-static functions here, I think it would be quite desirable for the bounds checking to live there. Since hvm_allow_{get,set}_param() are specifically helpers of the two earlier named functions, checks consistently living there would as well be fine with me. Jan