linux-kernel - Re: [PATCH v2] tpm: use a map for tpm2_calc_ordinal

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Message-ID: <aM1tH2RNVgRnuZ5w@mail.hallyn.com>
Date: Fri, 19 Sep 2025 09:47:59 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: "Serge E. Hallyn" <serge@...lyn.com>, linux-integrity@...r.kernel.org,
	Frédéric Jouen <fjouen@...lsq.com>,
	Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:KEYS-TRUSTED" <keyrings@...r.kernel.org>,
	"open list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2] tpm: use a map for tpm2_calc_ordinal_duration()

On Fri, Sep 19, 2025 at 10:05:58AM +0300, Jarkko Sakkinen wrote:
> On Thu, Sep 18, 2025 at 10:49:28PM -0500, Serge E. Hallyn wrote:
> > On Thu, Sep 18, 2025 at 10:30:18PM +0300, Jarkko Sakkinen wrote:
> > > The current shenanigans for duration calculation introduce too much
> > > complexity for a trivial problem, and further the code is hard to patch and
> > > maintain.
> > > 
> > > Address these issues with a flat look-up table, which is easy to understand
> > > and patch. If leaf driver specific patching is required in future, it is
> > > easy enough to make a copy of this table during driver initialization and
> > > add the chip parameter back.
> > > 
> > > 'chip->duration' is retained for TPM 1.x.
> > > 
> > > As the first entry for this new behavior address TCG spec update mentioned
> > > in this issue:
> > > 
> > > https://github.com/raspberrypi/linux/issues/7054
> > > 
> > > Therefore, for TPM_SelfTest the duration is set to 3000 ms.

D'oh!  It *was* in the commit message all along, sorry.

> > > This does not categorize a as bug, given that this is introduced to the
> > > spec after the feature was originally made.
> > > 
> > > Cc: Frédéric Jouen <fjouen@...lsq.com>
> > > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>

Looks good, thank you.

Reviewed-by: Serge Hallyn <serge@...lyn.com>


> > fwiw (which shouldn't be much) looks good to me, but two questions,
> > one here and one below.
> > 
> > First, it looks like in the existing code it is possible for a tpm2
> > chip to set its own timeouts and then set the TPM_CHIP_FLAG_HAVE_TIMEOUTS
> > flag to avoid using the defaults, but I don't see anything using that
> > in-tree.  Is it possible that there are out of tree drivers that will be
> > sabotaged here?  Or am I misunderstanding that completely?
> 
> Good questions, and I can brief a bit about the context of the
> pre-existing art and this change.
> 
> This complexity was formed in 2014 when I originally developed TPM2
> support and the only available testing plaform was early Intel PTT with
> a flakky version of TPM2 support (e.g., no localities).
> 
> Since then we haven't had per leaf-driver divergence.
> 
> Further, I think that this type of layout is actually a  better fit if
> we ever need to quirks for command durations for a particular device, as
> then we can migrate to "copy and patch" semantics i.e., have a copy of
> this map in the chip structure.
> 
> As per out-of-tree drivers, it's unfortunate reality of out-of-tree
> drivers :-) However, this will definitely add some extra work, when
> backporting fixes (not overwhelmingly much).
> 
> BR, Jarkko