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 02A27C433E0 for ; Thu, 14 Jan 2021 15:49:50 +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 A0B8123A50 for ; Thu, 14 Jan 2021 15:49:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A0B8123A50 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.67268.119949 (Exim 4.92) (envelope-from ) id 1l04sW-0005km-D2; Thu, 14 Jan 2021 15:49:40 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 67268.119949; Thu, 14 Jan 2021 15:49:40 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l04sW-0005kf-9s; Thu, 14 Jan 2021 15:49:40 +0000 Received: by outflank-mailman (input) for mailman id 67268; Thu, 14 Jan 2021 15:49:39 +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 1l04iu-0002Sh-La for xen-devel@lists.xenproject.org; Thu, 14 Jan 2021 15:39:44 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id b10f933e-20d4-4214-b2bd-0791d0c6b377; Thu, 14 Jan 2021 15:38:28 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 66A63AEAB; Thu, 14 Jan 2021 15:38:27 +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: b10f933e-20d4-4214-b2bd-0791d0c6b377 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=1610638707; 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=oLfI5O1odNAJ2FlprWdwHJpbz3Zme4dt/wvDbg3b8jM=; b=RGKIGsIHwurRRLEgvM6Cm1e6HrGnR082hNzZ1BtOaqBmqIwegQtSjm6IjPmmSEKWytd4yy nnssj4qqzBSwCkdYyCA5ApC27fLFVjJWinOPcrQRpdEFoZ3vS+hwn8RpIb8L77QVC5gwnl R4hw/8f3oqtYJlQLbZ8bEpjpgFhmYw0= Subject: Re: [PATCH] common: don't require use of DOMID_SELF To: Andrew Cooper Cc: George Dunlap , Ian Jackson , Julien Grall , Stefano Stabellini , Wei Liu , "xen-devel@lists.xenproject.org" References: <72c9f0ec-81e3-63f9-2513-46e463642219@suse.com> <3c0ebca6-a5e9-36a8-cfeb-6abc0fc7c2af@citrix.com> From: Jan Beulich Message-ID: Date: Thu, 14 Jan 2021 16:38:27 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <3c0ebca6-a5e9-36a8-cfeb-6abc0fc7c2af@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 14.01.2021 16:01, Andrew Cooper wrote: > On 14/01/2021 14:02, Jan Beulich wrote: >> --- a/xen/common/grant_table.c >> +++ b/xen/common/grant_table.c >> @@ -2776,15 +2776,19 @@ struct gnttab_copy_buf { >> static int gnttab_copy_lock_domain(domid_t domid, bool is_gref, >> struct gnttab_copy_buf *buf) >> { >> - /* Only DOMID_SELF may reference via frame. */ >> - if ( domid != DOMID_SELF && !is_gref ) >> - return GNTST_permission_denied; >> - >> buf->domain = rcu_lock_domain_by_any_id(domid); >> >> if ( !buf->domain ) >> return GNTST_bad_domain; >> >> + /* Only the local domain may reference via frame. */ >> + if ( buf->domain != current->domain && !is_gref ) >> + { >> + rcu_unlock_domain(buf->domain); >> + buf->domain = NULL; >> + return GNTST_permission_denied; >> + } > > In this case, it's also a weird asymmetry where this is one grant table > operation which a privileged domain can't issue on behalf of an > unprivileged one. Well, in a way, perhaps. If it was useful, perhaps it would have been made work and allowed, so I wonder whether there simply is no good use for it? >> --- a/xen/common/page_alloc.c >> +++ b/xen/common/page_alloc.c >> @@ -2566,13 +2566,7 @@ __initcall(register_heap_trigger); >> >> struct domain *get_pg_owner(domid_t domid) >> { >> - struct domain *pg_owner = NULL, *curr = current->domain; >> - >> - if ( unlikely(domid == curr->domain_id) ) >> - { >> - gdprintk(XENLOG_WARNING, "Cannot specify itself as foreign domain\n"); >> - goto out; >> - } >> + struct domain *pg_owner; > > I'm not sure this is correct. > > It isn't a DOMID_SELF check.  It's a "confirm the nominated domid is > remote" check, and I don't see all the callers of this interface having > appropriate checks to prohibit trying to do a foreign operation on > oneself, however they specify the foreign domid. No, I don't think so. Prior to a625c335593e ("common: don't (kind of) open-code rcu_lock_domain_by_any_id()") DOMID_SELF was explicitly permitted. As of that change, it's implicitly permitted. I don't see how using DOMID_SELF would be okay when using the numeric ID isn't. (I'm not going to exclude there may be missing checks in some of the callers, but from prior audits I don't recall recognizing any.) Jan