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Thu, 29 Oct 2026 03:05:03 -0700 (PDT) Received: from localhost ([208.127.45.21]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c46bd7abf6asm705408566b.81.2026.10.29.03.05.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2026 03:05:03 -0700 (PDT) Date: Thu, 29 Oct 2026 11:04:58 +0100 From: Jiri Pirko To: Jason Gunthorpe Cc: linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, jgg@ziepe.ca, david.quigley@intel.com, lukas@wunner.de, ksinyuk@kernel.org, rodrigo.vivi@intel.com, cedric.xing@intel.com, sameo@meta.com, drdeeglaze@gmail.com, James.Bottomley@hansenpartnership.com, aik@amd.com, jpiotrowski@nvidia.com, qinkun@google.com, pgonda@google.com, jic23@kernel.org, alistair.francis@wdc.com, ankita@nvidia.com, suzuki.poulose@arm.com, kas@kernel.org, rick.p.edgecombe@intel.com, elena.reshetova@intel.com, dave.hansen@linux.intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, peter.fang@intel.com Subject: Re: [PATCH RFC 14/20] attestation: Add the base family specification and generated files Message-ID: References: <20261015145053.3664509-1-jiri@resnulli.us> <20261015145053.3664509-15-jiri@resnulli.us> <179302367452.58760.3782556786585774917.b4-review@b4> X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <179302367452.58760.3782556786585774917.b4-review@b4> Mon, Oct 26, 2026 at 03:07:54PM +0100, jgg@nvidia.com wrote: [..] > >======= > >device-get: > request: {} > reply: > caps: > evidence?: > min-challenge-length: uint > max-challenge-length: uint > >Did anyone implement a variable length challenge? That seems a bit >strange. There is also a very important crypto warning here that the Yes. TPM2_Quote accepts variable-length qualifyingData, represented by TPM2B_DATA with an explicit length. This varies per request on the same TPM: [1] TPM Library Part 2, section 10.3.3, page 136: TPM2B_DATA. https://medias.cdn.trustedcomputinggroup.org/production/Trusted_Platform_Module_2_0_Library_Part_2_Structures_Version_185_pub_c0a962a931.pdf#page=136 [2] Part 3, section 18.4.2, page 158: TPM2_Quote qualifyingData. https://medias.cdn.trustedcomputinggroup.org/production/Trusted_Platform_Module_2_0_Library_Part_3_Commands_Version_185_pub_87a5c10230.pdf#page=158 The PSA Attestation API, section 4.4, also requires one implementation to support 32-, 48-, and 64-byte challenges: https://arm-software.github.io/psa-api/attestation/1.0/api/api.html FIRME DEN0149 1.0 ALP2, section 8.12, Table 8.23, page 100, likewise defines an explicit Platform challenge size parameter in x4[31:0]. FIRME itself does not mandate the specific 32/48/64-byte set: https://documentation-service.arm.com/static/699c3b70b60ef220b14ec14d?token=#page=100 >userspace use of the challenge must not create a "signing oracle". Ie >do not pass naked network data into the challenge.. Agreed that we should document safe challenge construction. [..]