linux-kernel - Re: [PATCH] tpm: Add module parameter for hwrng quality.

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Date:   Mon, 18 Jun 2018 13:33:06 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Louis Collard <louiscollard@...omium.org>,
        linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, apronin@...omium.org
Subject: Re: [PATCH] tpm: Add module parameter for hwrng quality.

On Mon, Jun 18, 2018 at 09:07:12PM +0300, Jarkko Sakkinen wrote:
> On Fri, Jun 08, 2018 at 02:54:38PM +0800, Louis Collard wrote:
> > It is now possible for drivers to easily specify a hwrng quality, however
> > most do not currently do this, and in cases where they do, it may be
> > desirable to override the driver-specified value with a user-specified
> > one. This patch adds a parameter to set or override the hwrng quality.
> > 
> > Signed-off-by: Louis Collard <louiscollard@...omium.org>
> >  drivers/char/tpm/tpm-chip.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> > index 0a62c19937b6..4def49cfc634 100644
> > +++ b/drivers/char/tpm/tpm-chip.c
> > @@ -33,6 +33,11 @@
> >  DEFINE_IDR(dev_nums_idr);
> >  static DEFINE_MUTEX(idr_lock);
> >  
> > +static short override_rng_quality = -1;
> > +module_param(override_rng_quality, short, 0644);
> 
> Should this be 600 i.e. not to leak this information?

There is a real push these days against adding module parameters, and
apparently, IMA can't function with TPM as a module.

Are you sure this shouldn't be done in some other way?

Jason