linux-kernel - Re: [PATCH v5 5/5] tpm: flush the auth session only when /dev/tpm0 is open

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Message-Id: <D4F7AVX5A3KI.235GJ3NRMGWV@kernel.org>
Date: Wed, 25 Sep 2024 10:53:03 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "James Bottomley"
 <James.Bottomley@...senPartnership.com>, <linux-integrity@...r.kernel.org>
Cc: <roberto.sassu@...wei.com>, <mapengyu@...il.com>,
 <stable@...r.kernel.org>, "Mimi Zohar" <zohar@...ux.ibm.com>, "David
 Howells" <dhowells@...hat.com>, "Paul Moore" <paul@...l-moore.com>, "James
 Morris" <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, "Peter
 Huewe" <peterhuewe@....de>, "Jason Gunthorpe" <jgg@...pe.ca>,
 <keyrings@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 5/5] tpm: flush the auth session only when /dev/tpm0
 is open

On Wed Sep 25, 2024 at 10:46 AM EEST, Jarkko Sakkinen wrote:
> On Wed Sep 25, 2024 at 10:42 AM EEST, Jarkko Sakkinen wrote:
> > Fair enough. I can buy this.
> >
> > I'll phrase it that (since it was mentioned in the bugzilla comment)
> > in the bug in question the root is in PCR extend but since in my own
> > tests I got overhead from trusted keys I also mention that it overally
> > affects also that and tpm2_get_random().
>
> I do not want to take null key flushing away although I got the
> reasoning given the small amount of time is saved (maybe 25-50 ms
> in my QEMU setup if I recall correctly) but it would make sense to
> squash it auth session patch.
>
> I'll also check 1/2 and 2/2 if I'm doing too much in them. Not
> adding any tags to v6 and it really makes sense to develop 
> benchmarks and not rush with the new version now that I got
> also your feedback, since it is past rc1 timeline.
>
> Good target rcX would be around rc3.

I have to admit this: I had blind spot on that PCR extend comment
because I did not get hits on that when testing this so it definitely
needs to be documented. I spotted it only yesterday.

BR, Jarkko