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From:   Janne Karhunen <janne.karhunen@gmail.com>
Date:   Wed, 16 Oct 2019 14:16:20 +0300
Message-ID: <CAE=Ncrb_7wQsv0_EvZWe5-WA2UU_GywgfnVo7hC-FDTY6bzpFQ@mail.gmail.com>
Subject: Re: [PATCH] tpm: Salt tpm_get_random() result with get_random_bytes()
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     linux-integrity@vger.kernel.org,
        David Safford <david.safford@ge.com>,
        Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        open list <linux-kernel@vger.kernel.org>,
        Mimi Zohar <zohar@linux.ibm.com>
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On Wed, Oct 16, 2019 at 1:41 PM Jarkko Sakkinen
<jarkko.sakkinen@linux.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.


--
Janne