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Thu, 29 Oct 2026 03:07:52 -0700 (PDT) Received: from localhost ([208.127.45.21]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c46bd520838sm715397566b.31.2026.10.29.03.07.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2026 03:07:51 -0700 (PDT) Date: Thu, 29 Oct 2026 11:07:47 +0100 From: Jiri Pirko To: Dave Jiang 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 00/20] attestation: Add a common subsystem and TDX support Message-ID: References: <20261015145053.3664509-1-jiri@resnulli.us> <592d643f-e97d-4de8-9a87-e47d57dc8457@intel.com> X-Mailing-List: kvm@vger.kernel.org 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: <592d643f-e97d-4de8-9a87-e47d57dc8457@intel.com> Tue, Oct 27, 2026 at 07:43:04PM +0100, dave.jiang@intel.com wrote: > > >On 10/15/26 7:50 AM, Jiri Pirko wrote: >> From: Jiri Pirko >> [..] >3. Jason asked on 14/20 whether anyone needs a variable-length challenge. I > don't think devices need a range. A plain read sends an empty challenge, and > an SPDM GET_MEASUREMENTS nonce is "NL = 32 or 0". Your TDX provider always > takes 64 (attestation_tdx_evidence_caps). https://lore.kernel.org/all/auMX4kbsflE9kK3Q@FV6GYCPJ69/ > > A device needs exactly two lengths: 0 for a plain read and 32 for a refresh. > struct attestation_evidence_caps only holds a single min/max range. It's > checked on every request in attestation_evidence_request_decode(), and any > range that allows both 0 and 32 also allows everything in between. > > To work around that, my provider declares 0-64 and PCI/TSM rejects any length Perhaps just omit the challenge attr in that case would be the best way? > other than the backend's nonce size, 32 for both backends I ran. Could the > caps give one exact challenge length instead of a range, plus a flag that > also allows an empty challenge? A device provider would set 32 with the flag, > and your TDX provider 64 without it. > [..]