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AHgh+Rog2aTypjYSn5T6Afj3IJqUVjwNkJg48DyvyRLS1URXGyiMCyIqYF0bS/Fvr1Fk2zrKqSY=@vger.kernel.org X-Gm-Message-State: AOJu0YxO9X+e7E8epdXF5AE6uphAm8ZIXI5Yo+6AE7wbubfGYPjCqfdG N4o88K8LQgtfIMzZSG4LNxMesHp8iuPFKu9x3IjTYfPK07kR9Rkkw9kYnpSlFTRq7jCO8yhe/CS g3jBZZA== X-Received: from plbkr8.prod.google.com ([2002:a17:903:808:b0:2cc:8741:f340]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:2cb:b0:2ca:d658:d874 with SMTP id d9443c01a7336-2d345713af3mr80782795ad.23.1786553027152; Wed, 12 Aug 2026 09:43:47 -0700 (PDT) Date: Wed, 12 Aug 2026 09:43:46 -0700 In-Reply-To: <86d532f33816cd4fa3e29c40079a6003abf89324.camel@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260729122939.1340412-1-peter.fang@intel.com> <80b4ea89ebf17398c3bee21d157c7f97ea32aadf.camel@intel.com> <86d532f33816cd4fa3e29c40079a6003abf89324.camel@intel.com> Message-ID: Subject: Re: [PATCH v3 0/4] tdx-guest: Make Quote buffer size dynamic From: Sean Christopherson To: Rick P Edgecombe Cc: "hpa@zytor.com" , Xiaoyao Li , "bp@alien8.de" , "kas@kernel.org" , "binbin.wu@linux.intel.com" , "x86@kernel.org" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "mingo@redhat.com" , "dave.hansen@linux.intel.com" , "linux-kernel@vger.kernel.org" , Artem Bityutskiy , Peter Fang , "tglx@kernel.org" , "linux-coco@lists.linux.dev" , "kvm@vger.kernel.org" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Wed, Aug 12, 2026, Rick P Edgecombe wrote: > On Wed, 2026-08-12 at 07:08 -0700, Sean Christopherson wrote: > > > =C2=A0 |Normal quote=C2=A0=C2=A0=C2=A0 |Migration quote |Report size|= Quote size|uAPI location=C2=A0 | > > > -|----------------|----------------|-----------|----------|----------= -----| > > > 1|Platform scoped |Platform scoped |Grows=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0 |Grows=C2=A0=C2=A0=C2=A0=C2=A0 |TDX host driver| > >=20 > > With my KVM hat on, this option looks very attractive. > >=20 > > And with the caveat that I'm most definitely not an attestation expert,= from a > > separate of concerns perspective, IMO it seems like the report should c= ontain > > the TD-specific information while the quote just wraps that information= in > > platform-specific goo. > >=20 > > In other words, to me, TD-scoped quotes feel like a hack that was throw= n in to > > avoid having to modify the guest because y'all didn't plan ahead. >=20 > Caveman crypto person here too.=C2=A0It seems scattered and makes me simi= larly > suspicious about some lack of planning. But I kind of came to a different > conclusion on what went wrong. >=20 > It seems to me that from the overall solution level, the report should ne= ver > have had the details in it. It should just be some nonce or some type of = thing > that can tie the guest request to the quote that it ends up getting > back.=C2=A0Doesn't it seem weird to get a bunch of details from the TDX m= odule, then > pass them from the guest to host KVM to host userspace then back to the T= DX > module... which already had all those details? Hmm, my mental model of this is that the report contains the "real" payload= , i.e. the metadata describing what is running and whatnot, while the quote effect= ively signs the payload to prove the provenance of the report. That's why I view= the report as TD-specific (what's running) and the quote as platform-specific (= provides root of trust). > My understanding was that the original SGX attestation was a complicator = of the > design of this stuff. Because I'm not sure that SGX had all those details= about > the TD. In fact I can't see how it could have. Is that right Peter? So it= needs > them all to be passed in. All the extra validations etc of this shuffling= is > TDX's problems to deal with, but for Linux, it would be at least a lot le= ss > confusing if there was not two things that have the TD details in them. >=20 > That said, from KVM POV, (1) kicks the attestation out of KVM. I see the > benefit. But a TD quote is a TD scoped operation in concept. To me at lea= st.