Re: [PATCH v3] tpm: Disable RNG for all AMD fTPMs

[Mario Limonciello <mario.limonciello@amd.com>]

On 8/4/23 17:54, Jarkko Sakkinen wrote:
> On Thu Aug 3, 2023 at 9:24 PM EEST, Mario Limonciello wrote:
>> The TPM RNG functionality is not necessary for entropy when the CPU
>> already supports the RDRAND instruction. The TPM RNG functionality
>> was previously disabled on a subset of AMD fTPM series, but reports
>> continue to show problems on some systems causing stutter root caused
>> to TPM RNG functionality.
>>
>> Expand disabling TPM RNG use for all AMD fTPMs whether they have versions
>> that claim to have fixed or not. To accomplish this, move the detection
>> into part of the TPM CRB registration and add a flag indicating that
>> the TPM should opt-out of registration to hwrng.
>>
>> Cc: stable@vger.kernel.org # 5.5+
>> Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources")
>> Fixes: f1324bbc4011 ("tpm: disable hwrng for fTPM on some AMD designs")
>> Fixes: 3ef193822b25 ("tpm_crb: fix fTPM on AMD Zen+ CPUs")
>> Reported-by: daniil.stas@posteo.net
>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217719
>> Reported-by: bitlord0xff@gmail.com
>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217212
>> Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> 
> I will skip rc5 and send this for rc6 on Monday.
> 
> Has anyone with suitable AMD system tested this?

Probably obvious; but I tested with a system that can support both dTPM 
and fTPM and swapped between the two before I sent it.