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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 622E6C38A2A for ; Thu, 7 May 2020 13:38:41 +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 3FC4D20643 for ; Thu, 7 May 2020 13:38:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FC4D20643 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jWgjO-0003zw-QV; Thu, 07 May 2020 13:38:30 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jWgjO-0003zq-48 for xen-devel@lists.xenproject.org; Thu, 07 May 2020 13:38:30 +0000 X-Inumbo-ID: 09028b66-9068-11ea-9f1a-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 09028b66-9068-11ea-9f1a-12813bfff9fa; Thu, 07 May 2020 13:38:29 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 4D582AC44; Thu, 7 May 2020 13:38:31 +0000 (UTC) Subject: Re: [PATCH 11/16] x86/spec-ctrl: Adjust DO_OVERWRITE_RSB to be shadow stack compatible To: Andrew Cooper References: <20200501225838.9866-1-andrew.cooper3@citrix.com> <20200501225838.9866-12-andrew.cooper3@citrix.com> <3c01d6c3-5a61-018b-13df-6e75256f6d6c@suse.com> From: Jan Beulich Message-ID: Date: Thu, 7 May 2020 15:38:27 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Xen-devel , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 07.05.2020 15:25, Andrew Cooper wrote: > On 07/05/2020 14:22, Jan Beulich wrote: >> On 02.05.2020 00:58, Andrew Cooper wrote: >>> @@ -114,6 +114,16 @@ >>> sub $1, %ecx >>> jnz .L\@_fill_rsb_loop >>> mov %\tmp, %rsp /* Restore old %rsp */ >>> + >>> +#ifdef CONFIG_XEN_SHSTK >>> + mov $1, %ecx >>> + rdsspd %ecx >>> + cmp $1, %ecx >>> + je .L\@_shstk_done >>> + mov $64, %ecx /* 64 * 4 bytes, given incsspd */ >>> + incsspd %ecx /* Restore old SSP */ >>> +.L\@_shstk_done: >>> +#endif >> The latest here I wonder why you don't use alternatives patching. >> I thought that's what you've introduced the synthetic feature >> flag for. > > We're already in the middle of an alternative and they don't nest.  More > importantly, this path gets used on the BSP, after patching and before > CET gets enabled. Oh, I should have noticed this. The first point could be dealt with, but I agree the second pretty much rules out patching. Reviewed-by: Jan Beulich Jan