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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 36E7BC4361B for ; Thu, 17 Dec 2020 12:14:58 +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 C6E77238E8 for ; Thu, 17 Dec 2020 12:14:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C6E77238E8 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.55902.97508 (Exim 4.92) (envelope-from ) id 1kpsB4-0008Op-Jt; Thu, 17 Dec 2020 12:14:38 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 55902.97508; Thu, 17 Dec 2020 12:14:38 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kpsB4-0008Oi-Gy; Thu, 17 Dec 2020 12:14:38 +0000 Received: by outflank-mailman (input) for mailman id 55902; Thu, 17 Dec 2020 12:14:37 +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 1kpsB3-0008Oc-DQ for xen-devel@lists.xenproject.org; Thu, 17 Dec 2020 12:14:37 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id e92a102d-a6a6-48f1-9f82-3f6470365b82; Thu, 17 Dec 2020 12:14:35 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 98737AC7F; Thu, 17 Dec 2020 12:14:34 +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: e92a102d-a6a6-48f1-9f82-3f6470365b82 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=1608207274; 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=xrphdW29sKqk78WD/Xl6dHk4g7FXa40Q7mkMEDngeVc=; b=V9FIZWuOIwamNxZyRj7jIcvuH5dYpVaea+97qytNyjFEkEEL2Nxu0MdRRuyCkmlSFIV3sL 6xUlUIeYt7emk/4a/MiZWn2OtcaVeI9voyqZHj9PssnT7qucoBgiJdHkX5KVNqKTyr0ANw C2kodxqMpN9p3QvF6lf6+pj0kcfJ/Hs= Subject: Re: [PATCH v3 5/8] xen/hypfs: add support for id-based dynamic directories To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Cc: Andrew Cooper , George Dunlap , Ian Jackson , Julien Grall , Stefano Stabellini , Wei Liu , xen-devel@lists.xenproject.org References: <20201209160956.32456-1-jgross@suse.com> <20201209160956.32456-6-jgross@suse.com> <2894a231-9150-7c09-cc5c-7ef52087acf5@suse.com> From: Jan Beulich Message-ID: <5e0ac85e-ecba-86ad-b350-ff30e3a40a68@suse.com> Date: Thu, 17 Dec 2020 13:14:34 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 17.12.2020 12:32, Jürgen Groß wrote: > On 17.12.20 12:28, Jan Beulich wrote: >> On 09.12.2020 17:09, Juergen Gross wrote: >>> +static const struct hypfs_entry *hypfs_dyndir_enter( >>> + const struct hypfs_entry *entry) >>> +{ >>> + const struct hypfs_dyndir_id *data; >>> + >>> + data = hypfs_get_dyndata(); >>> + >>> + /* Use template with original enter function. */ >>> + return data->template->e.funcs->enter(&data->template->e); >>> +} >> >> At the example of this (applies to other uses as well): I realize >> hypfs_get_dyndata() asserts that the pointer is non-NULL, but >> according to the bottom of ./CODING_STYLE this may not be enough >> when considering the implications of a NULL deref in the context >> of a PV guest. Even this living behind a sysctl doesn't really >> help, both because via XSM not fully privileged domains can be >> granted access, and because speculation may still occur all the >> way into here. (I'll send a patch to address the latter aspect in >> a few minutes.) While likely we have numerous existing examples >> with similar problems, I guess in new code we'd better be as >> defensive as possible. > > What do you suggest? BUG_ON()? Well, BUG_ON() would be a step in the right direction, converting privilege escalation to DoS. The question is if we can't do better here, gracefully failing in such a case (the usual pair of ASSERT_UNREACHABLE() plus return/break/goto approach doesn't fit here, at least not directly). > You are aware that this is nothing a user can influence, so it would > be a clear coding error in the hypervisor? A user (or guest) can't arrange for there to be a NULL pointer, but if there is one that can be run into here, this would still require an XSA afaict. Jan