linux-kernel - Re: [PATCH] tpm: require to compile as part of the kernel

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Date:   Fri, 29 Jun 2018 12:11:00 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Winkler, Tomas" <tomas.winkler@...el.com>,
        Azhar Shaikh <azhar.shaikh@...el.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: require to compile as part of the kernel

On Fri, Jun 29, 2018 at 08:43:28PM +0300, Jarkko Sakkinen wrote:
> On Fri, Jun 29, 2018 at 09:31:41AM -0600, Jason Gunthorpe wrote:
> > On Fri, Jun 29, 2018 at 06:10:02PM +0300, Jarkko Sakkinen wrote:
> > > Do not allow to compile TPM core as a module. TPM defines a root of
> > > trust for integrity and keyring subsystems and should be always
> > > available and not be loaded from the user space. There is no a
> > > reasonable use case for a loadable module existing.
> > > 
> > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > >  drivers/char/tpm/Kconfig | 2 +-
> > >  include/linux/tpm.h      | 3 +--
> > >  2 files changed, 2 insertions(+), 3 deletions(-)
> > 
> > This doesn't really make sense..
> > 
> > The kconfig method is that if IMA requires TPM it should declare so
> > and TPM will become non-modular because IMA is non-modular.
> > 
> > There are lots of legitimate use cases for TPM that don't involve IMA
> > or keyring.
> 
> In what context would it make sense to have TPM core as a module? I
> forgot to add RFC tag this patch. Did not meant to push it to
> mainline but more to rise up the discussion.

The usual reasons for modules, embedded that wants minimize kernel
image size to minimize boot time - load modules after the system has
started.. Developers that wish to use module-reload to test the code
they are working on, etc.

Jason