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Mario Limonciello authored
AMD has issued an advisory indicating that having fTPM enabled in BIOS can cause "stuttering" in the OS. This issue has been fixed in newer versions of the fTPM firmware, but it's up to system designers to decide whether to distribute it. This issue has existed for a while, but is more prevalent starting with kernel 6.1 because commit b006c439 ("hwrng: core - start hwrng kthread also for untrusted sources") started to use the fTPM for hwrng by default. However, all uses of /dev/hwrng result in unacceptable stuttering. So, simply disable registration of the defective hwrng when detecting these faulty fTPM versions. As this is caused by faulty firmware, it is plausible that such a problem could also be reproduced by other TPM interactions, but this hasn't been shown by any user's testing or reports. It is hypothesized to be triggered more frequently by the use of the RNG because userspace software will fetch random numbers regularly. Intentionally continue to register other TPM functionality so that users that rely upon PCR measurements or any storage of data will still have access to it. If it's found later that another TPM functionality is exacerbating this problem a module parameter it can be turned off entirely and a module parameter can be introduced to allow users who rely upon fTPM functionality to turn it on even though this problem is present. Link: https://www.amd.com/en/support/kb/faq/pa-410 Link: https://bugzilla.kernel.org/show_bug.cgi?id=216989 Link: https://lore.kernel.org/all/20230209153120.261904-1-Jason@zx2c4.com/ Fixes: b006c439 ("hwrng: core - start hwrng kthread also for untrusted sources") Cc: stable@vger.kernel.org Cc: Jarkko Sakkinen <jarkko@kernel.org> Cc: Thorsten Leemhuis <regressions@leemhuis.info> Cc: James Bottomley <James.Bottomley@hansenpartnership.com> Tested-by: reach622@mailcuk.com Tested-by: Bell <1138267643@qq.com> Co-developed-by: Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
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