linux-kernel - Re: [PATCH] tpm: Detach page allocation from tpm

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Date:   Thu, 3 Oct 2019 21:33:06 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: Detach page allocation from tpm_buf

On Thu, Oct 03, 2019 at 11:24:21AM -0400, Mimi Zohar wrote:
> On Thu, 2019-10-03 at 14:33 +0300, Jarkko Sakkinen wrote:
> 
> > > > Will this delay the TPM initialization, causing IMA to go into "TPM
> > > > bypass mode"?
> > > 
> > > Of course it will delay the init.
> > > 
> > > As I've stated before the real fix for the bypass issue would be
> > > to make TPM as part of the core but this has not received much
> > > appeal. I think I've sent patch for this once.
> 
> IMA initialization is way later than the TPM.  IMA is on the
> late_initcall(), while the TPM is on the subsys_initcall().  I'm not
> sure moving the TPM to core would make a difference.  There must be a
> way of deferring IMA until after the TPM has been initialized.  Any
> suggestions would be much appreciated.
> 
> (The TPM on the Pi still has a dependency on clock.) 

Right. I seriously need to study IMA code in near future with time.

> > It has been like that people reject a fix to a race condition and
> > then I get complains on adding minor latency to the init because
> > of the existing race. It is ridicilous, really.
> 
> I agree, but adding any latency will cause a regression.

OK, I get the picture here now. I have to some day look at the IMA
code and see if I could draft something that would improve the
situation. Thanks for explaining all this!

/Jarkko