Re: [PATCH RFC 14/20] attestation: Add the base family specification and generated files

[Jiri Pirko]

Thu, Oct 29, 2026 at 07:43:24PM +0100, jgg@xxxxxxxxxx wrote:
>On Thu, Oct 29, 2026 at 11:04:58AM +0100, Jiri Pirko wrote:
>> Mon, Oct 26, 2026 at 03:07:54PM +0100, jgg@xxxxxxxxxx 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
>
>I feel like userspace needs to know the difference between 'any size
>between 0 and 100 and 'exactly one of 32, 64, 128' ?

True.