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@vger.kernel.org # 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@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 Signed-off-by: Mario Limonciello mario.limonciello@amd.com
Hopefully future AMD hardware won't be broken and we can revisit this. Until then, LGTM:
Reviewed-by: Jason A. Donenfeld Jason@zx2c4.com
Thanks. I'll add your tag.
BR, Jarkko