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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 5E8B9C48BF6 for ; Thu, 7 Mar 2024 13:56:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1riEEW-00029X-RR; Thu, 07 Mar 2024 08:56:28 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1riEES-0001jr-9H for qemu-devel@nongnu.org; Thu, 07 Mar 2024 08:56:24 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1riEEP-0006n1-RT for qemu-devel@nongnu.org; Thu, 07 Mar 2024 08:56:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709819780; 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=8cvkgaBtTuoC3Wc+2TSS7zKm5F0tiDeYXB0fHBJZoHc=; b=dwVVHwsY1f/ZgZb97Pp15M8q0ZQN+OA+gCaynGYmy5A5wXiilJ6KXphzSvHnKcVasRz/bG 0GlvxG2OfDmvP4IJg0Me+Xm33C3Bl8QcSjghkSadJ5lR/d0EQwBVQPntOzbSPFfDEcn1QM iayqVoAmpGS8qRWIPU9BcXLofOvmMwE= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-551-ujLVtXAtM5ufl9nioQN28g-1; Thu, 07 Mar 2024 08:56:17 -0500 X-MC-Unique: ujLVtXAtM5ufl9nioQN28g-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 95AF41E441D5; Thu, 7 Mar 2024 13:56:16 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4F4C017A96; Thu, 7 Mar 2024 13:56:16 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4030821E6A24; Thu, 7 Mar 2024 14:56:15 +0100 (CET) From: Markus Armbruster To: Xiaoyao Li Cc: Paolo Bonzini , David Hildenbrand , Igor Mammedov , Eduardo Habkost , Marcel Apfelbaum , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Yanan Wang , "Michael S. Tsirkin" , Richard Henderson , Ani Sinha , Peter Xu , Cornelia Huck , Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Eric Blake , Marcelo Tosatti , kvm@vger.kernel.org, qemu-devel@nongnu.org, Michael Roth , Claudio Fontana , Gerd Hoffmann , Isaku Yamahata , Chenyi Qiang Subject: Re: [PATCH v5 30/65] i386/tdx: Support user configurable mrconfigid/mrowner/mrownerconfig In-Reply-To: <0f3df4b7-ffb9-4fc5-90eb-8a1d6fea5786@intel.com> (Xiaoyao Li's message of "Thu, 7 Mar 2024 19:24:04 +0800") References: <20240229063726.610065-1-xiaoyao.li@intel.com> <20240229063726.610065-31-xiaoyao.li@intel.com> <87edcv1x9j.fsf@pond.sub.org> <871q8vxuzx.fsf@pond.sub.org> <4602df24-029e-4a40-bdec-1b0a6aa30a3c@intel.com> <87v85yv3j9.fsf@pond.sub.org> <0f3df4b7-ffb9-4fc5-90eb-8a1d6fea5786@intel.com> Date: Thu, 07 Mar 2024 14:56:15 +0100 Message-ID: <87ttli87sw.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.583, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Xiaoyao Li writes: > On 3/7/2024 4:39 PM, Markus Armbruster wrote: >> Xiaoyao Li writes: >>=20 >>> On 2/29/2024 9:25 PM, Markus Armbruster wrote: >>>> Xiaoyao Li writes: >>>> >>>>> On 2/29/2024 4:37 PM, Markus Armbruster wrote: >>>>>> Xiaoyao Li writes: >>>>>> >>>>>>> From: Isaku Yamahata >>>>>>> >>>>>>> Three sha384 hash values, mrconfigid, mrowner and mrownerconfig, of= a TD >>>>>>> can be provided for TDX attestation. Detailed meaning of them can be >>>>>>> found: https://lore.kernel.org/qemu-devel/31d6dbc1-f453-4cef-ab08-4= 813f4e0ff92@intel.com/ >>>>>>> >>>>>>> Allow user to specify those values via property mrconfigid, mrowner= and >>>>>>> mrownerconfig. They are all in base64 format. >>>>>>> >>>>>>> example >>>>>>> -object tdx-guest, \ >>>>>>> mrconfigid=3DASNFZ4mrze8BI0VniavN7wEjRWeJq83vASNFZ4mrze8BI0Vni= avN7wEjRWeJq83v,\ >>>>>>> mrowner=3DASNFZ4mrze8BI0VniavN7wEjRWeJq83vASNFZ4mrze8BI0VniavN= 7wEjRWeJq83v,\ >>>>>>> mrownerconfig=3DASNFZ4mrze8BI0VniavN7wEjRWeJq83vASNFZ4mrze8BI0= VniavN7wEjRWeJq83v >>>>>>> >>>>>>> Signed-off-by: Isaku Yamahata >>>>>>> Co-developed-by: Xiaoyao Li >>>>>>> Signed-off-by: Xiaoyao Li >>>> [...] >>>> >>>>>>> diff --git a/qapi/qom.json b/qapi/qom.json >>>>>>> index 89ed89b9b46e..cac875349a3a 100644 >>>>>>> --- a/qapi/qom.json >>>>>>> +++ b/qapi/qom.json >>>>>>> @@ -905,10 +905,25 @@ >>>>>>> # pages. Some guest OS (e.g., Linux TD guest) may require t= his to >>>>>>> # be set, otherwise they refuse to boot. >>>>>>> # >>>>>>> +# @mrconfigid: ID for non-owner-defined configuration of the guest= TD, >>>>>>> +# e.g., run-time or OS configuration (base64 encoded SHA384 di= gest). >>>>>>> +# (A default value 0 of SHA384 is used when absent). >>>>>> >>>>>> Suggest to drop the parenthesis in the last sentence. >>>>>> >>>>>> @mrconfigid is a string, so the default value can't be 0. Actually, >>>>>> it's not just any string, but a base64 encoded SHA384 digest, which >>>>>> means it must be exactly 96 hex digits. So it can't be "0", either.= It >>>>>> could be >>>>>> "0000000000000000000000000000000000000000000000000000000000000000000= 00000000000000000000000000000". >>>>> >>>>> I thought value 0 of SHA384 just means it. >>>>> >>>>> That's my fault and my poor english. >>>> >>>> "Fault" is too harsh :) It's not as precise as I want our interface >>>> documentation to be. We work together to get there. >>>> >>>>>> More on this below. >>>>>> >>>>>>> +# >>>>>>> +# @mrowner: ID for the guest TD=E2=80=99s owner (base64 encoded SH= A384 digest). >>>>>>> +# (A default value 0 of SHA384 is used when absent). >>>>>>> +# >>>>>>> +# @mrownerconfig: ID for owner-defined configuration of the guest = TD, >>>>>>> +# e.g., specific to the workload rather than the run-time or OS >>>>>>> +# (base64 encoded SHA384 digest). (A default value 0 of SHA384= is >>>>>>> +# used when absent). >>>>>>> +# >>>>>>> # Since: 9.0 >>>>>>> ## >>>>>>> { 'struct': 'TdxGuestProperties', >>>>>>> - 'data': { '*sept-ve-disable': 'bool' } } >>>>>>> + 'data': { '*sept-ve-disable': 'bool', >>>>>>> + '*mrconfigid': 'str', >>>>>>> + '*mrowner': 'str', >>>>>>> + '*mrownerconfig': 'str' } } >>>>>>> ## >>>>>>> # @ThreadContextProperties: >>>>>>> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c >>>>>>> index d0ad4f57b5d0..4ce2f1d082ce 100644 >>>>>>> --- a/target/i386/kvm/tdx.c >>>>>>> +++ b/target/i386/kvm/tdx.c >>>>>>> @@ -13,6 +13,7 @@ >>>>>>> #include "qemu/osdep.h" >>>>>>> #include "qemu/error-report.h" >>>>>>> +#include "qemu/base64.h" >>>>>>> #include "qapi/error.h" >>>>>>> #include "qom/object_interfaces.h" >>>>>>> #include "standard-headers/asm-x86/kvm_para.h" >>>>>>> @@ -516,6 +517,7 @@ int tdx_pre_create_vcpu(CPUState *cpu, Error **= errp) >>>>>>> X86CPU *x86cpu =3D X86_CPU(cpu); >>>>>>> CPUX86State *env =3D &x86cpu->env; >>>>>>> g_autofree struct kvm_tdx_init_vm *init_vm =3D NULL; >>>>>>> + size_t data_len; >>>>>>> int r =3D 0; >>>>>>> object_property_set_bool(OBJECT(cpu), "pmu", false, &error_a= bort); >>>>>>> @@ -528,6 +530,38 @@ int tdx_pre_create_vcpu(CPUState *cpu, Error *= *errp) >>>>>>> init_vm =3D g_malloc0(sizeof(struct kvm_tdx_init_vm) + >>>>>>> sizeof(struct kvm_cpuid_entry2) * KVM_MA= X_CPUID_ENTRIES); >>>>>>> +#define SHA384_DIGEST_SIZE 48 >>>>>>> + >>>>>>> + if (tdx_guest->mrconfigid) { >>>>>>> + g_autofree uint8_t *data =3D qbase64_decode(tdx_guest->mrc= onfigid, >>>>>>> + strlen(tdx_guest->mrconfigid), &data= _len, errp); >>>>>>> + if (!data || data_len !=3D SHA384_DIGEST_SIZE) { >>>>>>> + error_setg(errp, "TDX: failed to decode mrconfigid"); >>>>>>> + return -1; >>>>>>> + } >>>>>>> + memcpy(init_vm->mrconfigid, data, data_len); >>>>>>> + } >>>>>> >>>>>> When @mrconfigid is absent, the property remains null, and this >>>>>> conditional is not executed. init_vm->mrconfigid[], an array of 6 >>>>>> __u64, remains all zero. How does the kernel treat that? >>>>> >>>>> A all-zero SHA384 value is still a valid value, isn't it? >>>>> >>>>> KVM treats it with no difference. >>>> >>>> Can you point me to the spot in the kernel where mrconfigid is used? >>> >>> https://github.com/intel/tdx/blob/66a10e258636fa8ec9f5ce687607bf2196a92= 341/arch/x86/kvm/vmx/tdx.c#L2322 >>> >>> KVM just copy what QEMU provides into its own data structure @td_params= . The format @of td_params is defined by TDX spec, and @td_params needs to = be passed to TDX module when initialize the context of TD via SEAMCALL(TDH.= MNG.INIT): https://github.com/intel/tdx/blob/66a10e258636fa8ec9f5ce687607bf= 2196a92341/arch/x86/kvm/vmx/tdx.c#L2450 >>> >>> >>> In fact, all the three SHA384 fields, will be hashed together with some= other fields (in td_params and other content of TD) to compromise the init= ial measurement of TD. >>> >>> TDX module doesn't care the value of td_params->mrconfigid. >> >> My problem is that I don't understand when and why users would omit the >> optional @mrFOO. > > When users don't care it and don't have an explicit value for them, they = can omit it. Then a default all-zero value is used. > > If making it mandatory field, then users have to explicit pass a all-zero= value when they don't care it. > >> I naively expected absent @mrFOO to mean something like "no attestation >> of FOO". >> >> But I see that they default to >> "00000000000000000000000000000000000000000000000000000000000000000000000= 0000000000000000000000000". >> >> If this zero value is special and means "no attestation", then we >> accidentally get no attestation when whatever is being hashed happens to >> hash to this zero value. Unlikely, but possible. >> >> If it's not special, then when and why is the ability to omit it useful? > > At some point, the zero value is special, because it is the default value= if no explicit one provided by user. But for TDX point of view, it is not = special. The field is a must for any TD, and whatever value it is, it will = be hashed into MRTD (Build-time Measurement Register) for later attestation. > > TDX architecture defines what fields are always hashed into measurement a= nd also provide other mechanism to hash optional field into measurement. Al= l this is known to users of TDX, and users can calculate the final measurem= ent by itself and compare to what gets reported by TDX to see they are iden= tical. > > For these three fields, they are must-to-have fields to be hashed into me= asurement. For user's convenience, we don't want to make it mandatory input= because not everyone cares it and have a specific value to input. > What people needs to know is that, when no explicit value is provided for= these three field, a all-zero value is used. Alright, the doc comment is not the place to educate me about TDX. Perhaps we can go with # @mrconfigid: ID for non-owner-defined configuration of the guest TD, # e.g., run-time or OS configuration (base64 encoded SHA384 digest). # Defaults to all zeroes.