On Thu Aug 3, 2023 at 4:45 PM EEST, Jason A. Donenfeld wrote:
> On Wed, Aug 02, 2023 at 07:25:33AM -0500, 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@xxxxxxxxxxxxxxx # 6.1.y+
> > Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources")
> > Fixes: f1324bbc4011 ("tpm: disable hwrng for fTPM on some AMD designs")
>
> Users can trigger this by reading from /dev/hwrng, which some userspace
> daemons are known to do. So I think the proper fixes tag and stable@
> version range actually begins with whenever fTPM support was introduced.
>
> > Reported-by: daniil.stas@xxxxxxxxxx
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217719
> > Reported-by: bitlord0xff@xxxxxxxxx
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217212
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
>
> Hopefully future AMD hardware won't be broken and we can revisit this.
> Until then, LGTM:
>
> Reviewed-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Thanks. I'll add your tag.
BR, Jarkko
