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=-6.4 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,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 98E6DC433E7 for ; Thu, 15 Oct 2020 07:00:44 +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 097EE22247 for ; Thu, 15 Oct 2020 07:00:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="GoiSPSAL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 097EE22247 Authentication-Results: mail.kernel.org; dmarc=fail (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 list by lists.xenproject.org with outflank-mailman.7108.18625 (Exim 4.92) (envelope-from ) id 1kSxFF-00027v-1H; Thu, 15 Oct 2020 07:00:13 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 7108.18625; Thu, 15 Oct 2020 07:00:13 +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" Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kSxFE-00027o-Tu; Thu, 15 Oct 2020 07:00:12 +0000 Received: by outflank-mailman (input) for mailman id 7108; Thu, 15 Oct 2020 07:00:11 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kSxFD-00027j-L1 for xen-devel@lists.xenproject.org; Thu, 15 Oct 2020 07:00:11 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id f1e7be84-3501-444e-b44b-ac9151109f10; Thu, 15 Oct 2020 07:00:10 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 52FC8AD83; Thu, 15 Oct 2020 07:00:09 +0000 (UTC) Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kSxFD-00027j-L1 for xen-devel@lists.xenproject.org; Thu, 15 Oct 2020 07:00:11 +0000 X-Inumbo-ID: f1e7be84-3501-444e-b44b-ac9151109f10 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id f1e7be84-3501-444e-b44b-ac9151109f10; Thu, 15 Oct 2020 07:00:10 +0000 (UTC) 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=1602745209; h=from:from:reply-to:subject:subject: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=stXzUWWNNn0tlYniH0/+yke3yDVk8S39bV2uE3ntIgc=; b=GoiSPSALtfp/uFpw8+LcU0TRAdcuBcEoQlikDW7cWDqBLxvZD7zfSMY9QXM+6vumg2WGHE 7e4Hs4JFbvg18QxBT45Tz/S0JReTZKlCi2t5B3h1h5RLx8hNj1PQp7aX4bcnx1pQHn1LGj 078BOWyRNhkLuWechv9gpKESz08raic= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 52FC8AD83; Thu, 15 Oct 2020 07:00:09 +0000 (UTC) Subject: Re: [PATCH] libelf: Handle PVH kernels lacking ENTRY elfnote To: Jason Andryuk Cc: xen-devel , Andrew Cooper , George Dunlap , Ian Jackson , Julien Grall , Stefano Stabellini , Wei Liu References: <20201014153150.83875-1-jandryuk@gmail.com> <6d373cae-c7dc-e109-1df3-ccbbe4bdd9c8@suse.com> From: Jan Beulich Message-ID: <4229544b-e98d-6f3c-14aa-a884c403ba74@suse.com> Date: Thu, 15 Oct 2020 09:00:09 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 14.10.2020 18:27, Jason Andryuk wrote: > On Wed, Oct 14, 2020 at 12:02 PM Jan Beulich wrote: >> >> On 14.10.2020 17:31, Jason Andryuk wrote: >>> Linux kernels only have an ENTRY elfnote when built with CONFIG_PV. A >>> kernel build CONFIG_PVH=y CONFIG_PV=n lacks the note. In this case, >>> virt_entry will be UNSET_ADDR, overwritten by the ELF header e_entry, >>> and fail the check against the virt address range. > > Oh, these should be CONFIG_XEN_PVH=y and CONFIG_XEN_PV=n > >>> Change the code to only check virt_entry against the virtual address >>> range if it was set upon entry to the function. >> >> Not checking at all seems wrong to me. The ELF spec anyway says >> "virtual address", so an out of bounds value is at least suspicious. >> >>> Maybe the overwriting of virt_entry could be removed, but I don't know >>> if there would be unintended consequences where (old?) kernels don't >>> have an elfnote, but do have an in-range e_entry? The failing kernel I >>> just looked at has an e_entry of 0x1000000. >> >> And if you dropped the overwriting, what entry point would we use >> in the absence of an ELF note? > > elf_xen_note_check currently has: > > /* PVH only requires one ELF note to be set */ > if ( parms->phys_entry != UNSET_ADDR32 ) > { > elf_msg(elf, "ELF: Found PVH image\n"); > return 0; > } > >> I'd rather put up the option of adjusting the entry (or the check), >> if it looks like a valid physical address. > > The function doesn't know if the image will be booted PV or PVH, so I > guess we do all the checks, but use 'parms->phys_entry != UNSET_ADDR32 > && parms->virt_entry == UNSET_ADDR' to conditionally skip checking > virt? Like Jürgen, the purpose of the patch hadn't become clear to me from reading the description. As I understand it now, we're currently refusing to boot such a kernel for no reason. If that's correct, perhaps you could say so in the description in a more direct way? As far as actual code adjustments go - how much of elf_xen_addr_calc_check() is actually applicable when booting PVH? And why is there no bounds check of ->phys_entry paralleling the ->virt_entry one? On the whole, as long as we don't know what mode we're planning to boot in, we can't skip any checks, as the mere presence of XEN_ELFNOTE_PHYS32_ENTRY doesn't mean that's also what gets used. Therefore simply bypassing any of the checks is not an option. In particular what you suggest would lead to failure to check e_entry-derived ->virt_entry when the PVH-specific note is present but we're booting in PV mode. For now I don't see how to address this without making the function aware of the intended booting mode. Jan