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

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Message-Id: <D46ZV5RXW7Z9.26N1IRXNRLV9X@kernel.org>
Date: Sun, 15 Sep 2024 19:22:04 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "James Bottomley" <James.Bottomley@...senPartnership.com>, "Roberto
 Sassu" <roberto.sassu@...weicloud.com>, "Linux regressions mailing list"
 <regressions@...ts.linux.dev>
Cc: <keyrings@...r.kernel.org>, "linux-integrity@...r.kernel.org"
 <linux-integrity@...r.kernel.org>, "LKML" <linux-kernel@...r.kernel.org>,
 "Pengyu Ma" <mapengyu@...il.com>
Subject: Re: [regression] significant delays when secureboot is enabled
 since 6.10

On Sun Sep 15, 2024 at 6:00 PM EEST, James Bottomley wrote:
> On Sun, 2024-09-15 at 17:50 +0300, Jarkko Sakkinen wrote:
> > On Sun Sep 15, 2024 at 4:59 PM EEST, James Bottomley wrote:
> > > On Sun, 2024-09-15 at 13:07 +0300, Jarkko Sakkinen wrote:
> > > > On Sun Sep 15, 2024 at 12:43 PM EEST, Jarkko Sakkinen wrote:
> > > > > When it comes to boot we should aim for one single
> > > > > start_auth_session during boot, i.e. different phases would
> > > > > leave that session open so that we don't have to load the
> > > > > context every single time.  I think it should be doable.
> > > > 
> > > > The best possible idea how to improve performance here would be
> > > > to transfer the cost from time to space. This can be achieved by
> > > > keeping null key permanently in the TPM memory during power
> > > > cycle.
> > > 
> > > No it's not at all.  If you look at it, the NULL key is only used
> > > to encrypt the salt for the start session and that's the operating
> > > taking a lot of time.  That's why the cleanest mitigation would be
> > > to save and restore the session.  Unfortunately the timings you
> > > already complain about still show this would be about 10x longer
> > > than a no-hmac extend so I'm still waiting to see if IMA people
> > > consider that an acceptable tradeoff.
> > 
> > The bug report does not say anything about IMA issues. Please read
> > the bug reports before commenting ;-) I will ignore your comment
> > because it is plain misleading information.
> > 
> > https://bugzilla.kernel.org/show_bug.cgi?id=219229
>
> Well, given that the kernel does no measured boot extends after the EFI
> boot stub (which isn't session protected) finishes, what's your theory
> for the root cause?

I don't think there is a silver bullet. Based on benchmark which showed
80% overhead from throttling the context reducing number of loads and
saves will cut a slice of the fat.

Since it is the low-hanging fruit I'll start with that. In other words,
I'm not going touch session loading and saving. I'll start with null
key loading and saving.

BR, Jarkko