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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 676D7C433DB for ; Wed, 3 Feb 2021 09:17:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 856F964E38 for ; Wed, 3 Feb 2021 09:17:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 856F964E38 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:49086 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7EHb-0008Eb-8q for qemu-devel@archiver.kernel.org; Wed, 03 Feb 2021 04:17:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52394) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7EFi-0007D9-Kq for qemu-devel@nongnu.org; Wed, 03 Feb 2021 04:15:10 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:42899) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7EFg-0008Jx-O7 for qemu-devel@nongnu.org; Wed, 03 Feb 2021 04:15:10 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612343708; 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: in-reply-to:in-reply-to:references:references; bh=lVoM1SEOdg9b6fe5xZYMPKeccXIZSp7ke8EvSNBpkds=; b=GPtQ/xAQAeZIHmTp24zzuDqrwjoLjtB++jPvXATkSds8wc6C/tJzCpDFagLKsQ3HZw9w4J vQXdji2Jl9o69+wc6kKIgv02gQERdzhkVeUi4Yb/Ko67/pL4vVqw8MKWfKs14N40hmqSB3 i09VqZ6uiJSnuryiaG+slxCX0F38ijw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-156-z5fJ_-pQOOOoCumL72bq2w-1; Wed, 03 Feb 2021 04:15:04 -0500 X-MC-Unique: z5fJ_-pQOOOoCumL72bq2w-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AA4AD81621; Wed, 3 Feb 2021 09:14:59 +0000 (UTC) Received: from work-vm (ovpn-115-70.ams2.redhat.com [10.36.115.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0FB6A7216C; Wed, 3 Feb 2021 09:14:56 +0000 (UTC) Date: Wed, 3 Feb 2021 09:14:54 +0000 From: "Dr. David Alan Gilbert" To: James Bottomley Subject: Re: [PATCH v2 1/2] pc: add parser for OVMF reset block Message-ID: <20210203091454.GB2950@work-vm> References: <20201214154429.11023-1-jejb@linux.ibm.com> <20201214154429.11023-2-jejb@linux.ibm.com> <20210126122207.GA4221@work-vm> <5bb73ef97b40eda029c54c9443274d5227372f8d.camel@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: <5bb73ef97b40eda029c54c9443274d5227372f8d.camel@linux.ibm.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.386, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: thomas.lendacky@amd.com, ashish.kalra@amd.com, brijesh.singh@amd.com, david.kaplan@amd.com, berrange@redhat.com, jon.grimm@amd.com, tobin@ibm.com, qemu-devel@nongnu.org, frankeh@us.ibm.com, Dov.Murik1@il.ibm.com, pbonzini@redhat.com, dovmurik@linux.vnet.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * James Bottomley (jejb@linux.ibm.com) wrote: > On Tue, 2021-01-26 at 12:22 +0000, Dr. David Alan Gilbert wrote: > > * James Bottomley (jejb@linux.ibm.com) wrote: > > > OVMF is developing a mechanism for depositing a GUIDed table just > > > below the known location of the reset vector. The table goes > > > backwards in memory so all entries are of the form > > > > > > |len| > > > > > > Where is arbtrary size and type, is a uint16_t and > > > describes the entire length of the entry from the beginning of the > > > data to the end of the guid. > > > > > > The foot of the table is of this form and for this case > > > describes the entire size of the table. The table foot GUID is > > > defined by OVMF as 96b582de-1fb2-45f7-baea-a366c55a082d and if the > > > table is present this GUID is just below the reset vector, 48 bytes > > > before the end of the firmware file. > > > > > > Add a parser for the ovmf reset block which takes a copy of the > > > block, > > > if the table foot guid is found, minus the footer and a function > > > for > > > later traversal to return the data area of any specified GUIDs. > > > > > > Signed-off-by: James Bottomley > > > > > > --- > > > > > > v2: fix brace warnings and return values > > > --- > > > hw/i386/pc_sysfw.c | 106 > > > +++++++++++++++++++++++++++++++++++++++++++ > > > include/hw/i386/pc.h | 4 ++ > > > 2 files changed, 110 insertions(+) > > > > > > diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c > > > index 92e90ff013..436b78c587 100644 > > > --- a/hw/i386/pc_sysfw.c > > > +++ b/hw/i386/pc_sysfw.c > > > @@ -124,6 +124,107 @@ void > > > pc_system_flash_cleanup_unused(PCMachineState *pcms) > > > } > > > } > > > > > > +#define OVMF_TABLE_FOOTER_GUID "96b582de-1fb2-45f7-baea- > > > a366c55a082d" > > > + > > > +static uint8_t *ovmf_table; > > > +static int ovmf_table_len; > > > + > > > +static void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, int > > > flash_size) > > > > Maybe size_t for flash_size? > > Heh, sure, who knows how big OVMF will get ... but I get the point > about an int overflow attack. To be honest I was more style than actually worrying about overflow; I like size_t for sizes. > > > +{ > > > + uint8_t *ptr; > > > + QemuUUID guid; > > > + int tot_len; > > > + > > > + /* should only be called once */ > > > + if (ovmf_table) { > > > + return; > > > + } > > > + > > > + /* > > > + * if this is OVMF there will be a table footer > > > + * guid 48 bytes before the end of the flash file. If it's > > > + * not found, silently abort the flash parsing. > > > + */ > > > + qemu_uuid_parse(OVMF_TABLE_FOOTER_GUID, &guid); > > > + guid = qemu_uuid_bswap(guid); /* guids are LE */ > > > + ptr = flash_ptr + flash_size - 48; > > > > I think since flash_size is coming from memory_region_size it's > > probably rounded to a page size by now, but perhaps we should always > > check we have enough space before we start moving pointers around > > I think OVMF must be at least a page, so I can add that check. > > > (Given that the OVMF binary might be provided by the guest owner, we > > have to consider it might be a vector to attack the hypervisor). > > > > > + if (!qemu_uuid_is_equal((QemuUUID *)ptr, &guid)) { > > > + return; > > > + } > > > + > > > + /* if found, just before is two byte table length */ > > > + ptr -= sizeof(uint16_t); > > > + tot_len = le16_to_cpu(*(uint16_t *)ptr) - sizeof(guid) - > > > sizeof(uint16_t); > > > + > > > + if (tot_len <= 0) { > > > + return; > > > + } > > > + > > > + ovmf_table = g_malloc(tot_len); > > > + ovmf_table_len = tot_len; > > > + > > > + /* > > > + * ptr is the foot of the table, so copy it all to the newly > > > + * allocated ovmf_table and then set the ovmf_table pointer > > > + * to the table foot > > > + */ > > > + memcpy(ovmf_table, ptr - tot_len, tot_len); > > > + ovmf_table += tot_len; > > > +} > > > + > > > +bool pc_system_ovmf_table_find(const char *entry, uint8_t **data, > > > + int *data_len) > > > +{ > > > + uint8_t *ptr = ovmf_table; > > > + int tot_len = ovmf_table_len; > > > + QemuUUID entry_guid; > > > + > > > + if (qemu_uuid_parse(entry, &entry_guid) < 0) { > > > + return false; > > > + } > > > + > > > + if (!ptr) { > > > + return false; > > > + } > > > + > > > + entry_guid = qemu_uuid_bswap(entry_guid); /* guids are LE */ > > > + while (tot_len > 0) { > > > + int len; > > > + QemuUUID *guid; > > > + > > > + /* > > > + * The data structure is > > > + * arbitrary length data > > > + * 2 byte length of entire entry > > > + * 16 byte guid > > > + */ > > > + guid = (QemuUUID *)(ptr - sizeof(QemuUUID)); > > > + len = le16_to_cpu(*(uint16_t *)(ptr - sizeof(QemuUUID) - > > > + sizeof(uint16_t))); > > > > Again I think we need to be checking tot_len > (sizeof(QemuUUID) + > > sizeof(uint16_t)) before doing this dereference. > > I can make the loop start > > while (tot_len > sizeof(QemuUUID) + sizeof(uint16_t)) Yep. Dave > > > + /* > > > + * just in case the table is corrupt, wouldn't want to > > > spin in > > > + * the zero case > > > + */ > > > + if (len < sizeof(QemuUUID) + sizeof(uint16_t)) { > > > + return false; > > > + } > > > + > > > + ptr -= len; > > > + tot_len -= len; > > > > and that len is smaller or equal to tot_len here. > > OK. > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK