Re: [PATCH 1/1] tpm: disable hwrng for fTPM on some AMD designs

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Feb 17, 2023 at 04:18:39PM +0100, Thorsten Leemhuis wrote:
> On 14.02.23 21:19, Mario Limonciello wrote:
> > 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 b006c439d58db ("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.
> 
> Hmm, no reply since Mario posted this.
> 
> Jarkko, James, what's your stance on this? Does the patch look fine from
> your point of view? And does the situation justify merging this on the
> last minute for 6.2? Or should we merge it early for 6.3 and then
> backport to stable?
> 
> Ciao, Thorsten

As I stated in earlier response: do we want to forbid tpm_crb in this case
or do we want to pass-through with a faulty firmware?

Not weighting either choice here I just don't see any motivating points
in the commit message to pick either, that's all.

BR, Jarkko