Re: [regression] significant delays when secureboot is enabled since 6.10

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2024-09-10 at 11:01 +0200, Linux regression tracking (Thorsten
Leemhuis) wrote:
> Hi, Thorsten here, the Linux kernel's regression tracker.
> 
> James, Jarkoo, I noticed a report about a regression in
> bugzilla.kernel.org that appears to be caused by this change of
> yours:
> 
> 6519fea6fd372b ("tpm: add hmac checks to tpm2_pcr_extend()") [v6.10-
> rc1]
> 
> As many (most?) kernel developers don't keep an eye on the bug
> tracker, I decided to forward it by mail. To quote from
> https://bugzilla.kernel.org/show_bug.cgi?id=219229 :
> 
> > When secureboot is enabled,
> > the kernel boot time is ~20 seconds after 6.10 kernel.
> > it's ~7 seconds on 6.8 kernel version.
> > 
> > When secureboot is disabled,
> > the boot time is ~7 seconds too.
> > 
> > Reproduced on both AMD and Intel platform on ThinkPad X1 and T14.
> > 
> > It probably caused autologin failure and micmute led not loaded on
> > AMD platform.
> 
> It was later bisected to the change mentioned above. See the ticket
> for more details.

We always suspected encryption and hmac would add overheads which is
why it's gated by a config option.  The way to fix this is to set

CONFIG_TCG_TPM_HMAC to N

of course, TPM transactions are then insecure, but it's the same state
as you were in before.

James