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=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 06E8AC433E6 for ; Mon, 22 Feb 2021 14:22:46 +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 A242764E41 for ; Mon, 22 Feb 2021 14:22:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A242764E41 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.88109.165556 (Exim 4.92) (envelope-from ) id 1lEC6f-0001YI-CN; Mon, 22 Feb 2021 14:22:37 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 88109.165556; Mon, 22 Feb 2021 14:22:37 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lEC6f-0001YA-98; Mon, 22 Feb 2021 14:22:37 +0000 Received: by outflank-mailman (input) for mailman id 88109; Mon, 22 Feb 2021 14:22:36 +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 1lEC6e-0001Xi-8w for xen-devel@lists.xenproject.org; Mon, 22 Feb 2021 14:22:36 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 891291a7-b0cb-4b34-9f74-99a3651c5535; Mon, 22 Feb 2021 14:22:34 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0422FACBF; Mon, 22 Feb 2021 14:22:34 +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: 891291a7-b0cb-4b34-9f74-99a3651c5535 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=1614003754; 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=ib9VfTPPSxo8nkl5zZBa2u0I49i3UgZnQHQiTXZfQbg=; b=emEbzEV0u0dr1jl9bUc3l0lBMjTGDhSryhOm32YbeFIbaK2AvyKydvOb6cbqr+Ky3xcGis j5TQ8fisz7SRytI0iY9aguv0rqtnEwuRfanbmc6NbRynPTGudwz/iR01S6CPX3VlGrNoGY 2+ddxLI0cmxxJEnFLksBn6D0E02QnYA= Subject: Re: [PATCH][4.15] x86: mirror compat argument translation area for 32-bit PV To: Andrew Cooper Cc: Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Ian Jackson , "xen-devel@lists.xenproject.org" References: <9eade40b-bd95-b850-2dec-f7def66c3c7b@citrix.com> From: Jan Beulich Message-ID: <77a36366-9157-c3d3-b1f0-211f4fc39a93@suse.com> Date: Mon, 22 Feb 2021 15:22:33 +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: <9eade40b-bd95-b850-2dec-f7def66c3c7b@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 22.02.2021 15:14, Andrew Cooper wrote: > On 22/02/2021 10:27, Jan Beulich wrote: >> Now that we guard the entire Xen VA space against speculative abuse >> through hypervisor accesses to guest memory, the argument translation >> area's VA also needs to live outside this range, at least for 32-bit PV >> guests. To avoid extra is_hvm_*() conditionals, use the alternative VA >> uniformly. >> >> While this could be conditionalized upon CONFIG_PV32 && >> CONFIG_SPECULATIVE_HARDEN_GUEST_ACCESS, omitting such extra conditionals >> keeps the code more legible imo. >> >> Fixes: 4dc181599142 ("x86/PV: harden guest memory accesses against speculative abuse") >> Signed-off-by: Jan Beulich >> >> --- a/xen/arch/x86/mm.c >> +++ b/xen/arch/x86/mm.c >> @@ -1727,6 +1727,11 @@ void init_xen_l4_slots(l4_pgentry_t *l4t >> (ROOT_PAGETABLE_FIRST_XEN_SLOT + slots - >> l4_table_offset(XEN_VIRT_START)) * sizeof(*l4t)); >> } >> + >> + /* Slot 511: Per-domain mappings mirror. */ >> + if ( !is_pv_64bit_domain(d) ) >> + l4t[l4_table_offset(PERDOMAIN2_VIRT_START)] = >> + l4e_from_page(d->arch.perdomain_l3_pg, __PAGE_HYPERVISOR_RW); > > This virtual address is inside the extended directmap. No. That one covers only the range excluding the last L4 slot. >  You're going to > need to rearrange more things than just this, to make it safe. I specifically picked that entry because I don't think further arrangements are needed. > While largely a theoretical risk as far as the directmap goes, there is > now a rather higher risk of colliding with the ERR_PTR() range.  Its bad > enough this infrastructure is inherently unsafe with 64bit PV guests, The ERR_PTR() range is still _far_ away from the sub-ranges we use in the per-domain area. Jan