linux-kernel - Re: [PATCH 1/1] tpm: disable hwrng for fTPM on some AMD designs

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Date:   Tue, 1 Aug 2023 13:36:20 +0200
From:   Mateusz Schyboll <dragonn@...pl>
To:     mario.limonciello@....com
Cc:     James.Bottomley@...senpartnership.com, Jason@...c4.com,
        daniil.stas@...teo.net, jarkko@...nel.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux@...inikbrodowski.net, regressions@...mhuis.info,
        stable@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [PATCH 1/1] tpm: disable hwrng for fTPM on some AMD designs

I was following the issue under or discord channel ROG for Linux and 
helping out some other users with it by shipping a kernel for Arch with 
disabled CONFIG_HW_RANDOM_TPM as the default recommend kernel for Arch 
for ROG laptops (as my device isn't affect by it because it is Ryzen 
4800HS).

I know it was discussed here 
https://bugzilla.kernel.org/show_bug.cgi?id=217212#c16 against allowing 
the user to disable fTPM to be used as a random source via a boot time 
parameter but I still I disagree with it.

Linux does have a parameter `random.trust_cpu` to control the random 
source from CPU, why they can not be a parameter like 
`random.trust_ftpm` (or `random.trust_tpm`)?

It might be my limited knowledge of this topic but to me it feels like 
if they is a trust_cpu then Linux should have trust_ftpm too.

Mateusz