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=-12.3 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 A5680C433DB for ; Tue, 26 Jan 2021 13:51:17 +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 56EDE2223D for ; Tue, 26 Jan 2021 13:51:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 56EDE2223D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org 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.75089.135110 (Exim 4.92) (envelope-from ) id 1l4OkO-00045I-7z; Tue, 26 Jan 2021 13:51:08 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 75089.135110; Tue, 26 Jan 2021 13:51:08 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4OkO-00045B-4x; Tue, 26 Jan 2021 13:51:08 +0000 Received: by outflank-mailman (input) for mailman id 75089; Tue, 26 Jan 2021 13:51:07 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4OkM-000453-Ux for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 13:51:06 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4OkK-0007Cd-6q; Tue, 26 Jan 2021 13:51:04 +0000 Received: from [54.239.6.190] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1l4OkJ-0001pV-Ti; Tue, 26 Jan 2021 13:51:04 +0000 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" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=1tc9hFA197322mpvaJnWk9qc2mRqp+pPobOFiWuFLH8=; b=B26tgF1foXTVjOu12duHTy66OQ 9xh4Dd3NHpUsok4LFbDoML+1Ksolxqf+7T4/Ova72QNGyYdD0hePkTScuUpovk757l7LkRqC9lw8C xaFh1/D8tN34GJ4o5b1N6BmBs1fZ4rUMCECkeCa3XDmO/huIWR1lmjmBzdxUTCPOI0h4=; Subject: Re: [PATCH v4 1/2] xen: EXPERT clean-up and introduce UNSUPPORTED To: Stefano Stabellini , xen-devel@lists.xenproject.org Cc: Stefano Stabellini , andrew.cooper3@citrix.com, george.dunlap@citrix.com, iwj@xenproject.org, jbeulich@suse.com, wl@xen.org References: <20210125212747.26676-1-sstabellini@kernel.org> From: Julien Grall Message-ID: <616b0552-33fc-360e-664c-44178e5afc6a@xen.org> Date: Tue, 26 Jan 2021 13:51:01 +0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210125212747.26676-1-sstabellini@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi Stefano, On 25/01/2021 21:27, Stefano Stabellini wrote: > config ARM_SSBD > - bool "Speculative Store Bypass Disable" if EXPERT > + bool "Speculative Store Bypass Disable (UNSUPPORTED)" if UNSUPPORTED > depends on HAS_ALTERNATIVE > default y > help > @@ -87,7 +87,7 @@ config ARM_SSBD > If unsure, say Y. > > config HARDEN_BRANCH_PREDICTOR > - bool "Harden the branch predictor against aliasing attacks" if EXPERT > + bool "Harden the branch predictor against aliasing attacks (UNSUPPORTED)" if UNSUPPORTED > default y > help > Speculation attacks against some high-performance processors rely on I read through the back and forth between Bertrand and Jan about "UNSUPPORTED". However, I still don't understand why those two options are moved to UNSUPPORTED. Both options will only build the code to enable the mitigation. The decision is still based on the processor you are running on. In addition to that, ARM_SSBD can also be forced enabled/disabled on the command line. A user may want to compile out the code if the target processor is not the affected by the two issues. This wouldn't be much different to Xen deciding to not enabling the mitigation. I would view the two options as supported but not security supported. So this seems to fit exactly in the definition of EXPERT rather than UNSUPPORTED. Cheers, -- Julien Grall