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>
