linux-kernel - Re: [PATCH] tpm: Salt tpm_get_random() result with get_random

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Message-ID: <20191016162312.GA6279@linux.intel.com>
Date:   Wed, 16 Oct 2019 19:23:28 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Janne Karhunen <janne.karhunen@...il.com>
Cc:     linux-integrity@...r.kernel.org,
        David Safford <david.safford@...com>,
        Pascal Van Leeuwen <pvanleeuwen@...imatrix.com>,
        James Bottomley <James.Bottomley@...senpartnership.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>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH] tpm: Salt tpm_get_random() result with get_random_bytes()

On Wed, Oct 16, 2019 at 02:16:20PM +0300, Janne Karhunen wrote:
> On Wed, Oct 16, 2019 at 1:41 PM Jarkko Sakkinen
> <jarkko.sakkinen@...ux.intel.com> wrote:
> 
> > > > get_random_bytes().  TPM could have a bug (making results predicatable),
> > > > backdoor or even an inteposer in the bus. Salting gives protections
> > > > against these concerns.
> > >
> > > The current issue in the randomness from my point of view is that
> > > encrypted filesystems, ima etc in common deployments require high
> > > quality entropy just few seconds after the system has powered on for
> > > the first time. It is likely that people want to keep their keys
> > > device specific, so the keys need to be generated on the first boot
> > > before any of the filesystems mount.
> >
> > This patch does not have the described issue.
> 
> My understanding was that you wanted to make the tpm_get_random() an
> alternative to get_random_bytes(), and one reason why one might want
> to do this is to work around the issues in get_random_bytes() in early
> init as it may not be properly seeded. But sure, if you this wasn't
> among the problems being solved then forget it.

I'm trying to get a framework on how rng's should be used in the
kernel. There doesn't seem to be one.

/Jarkko