linux-kernel - Re: [PATCH] security/keys/trusted: Allow operation without hardware TPM

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Date:   Thu, 21 Mar 2019 09:30:24 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] security/keys/trusted: Allow operation without hardware TPM

On Thu, Mar 21, 2019 at 7:27 AM Roberto Sassu <roberto.sassu@...wei.com> wrote:
>
> On 3/21/2019 2:54 PM, Jarkko Sakkinen wrote:
> > On Mon, Mar 18, 2019 at 04:45:13PM -0700, Dan Williams wrote:
> >> Rather than fail initialization of the trusted.ko module, arrange for
> >> the module to load, but rely on trusted_instantiate() to fail
> >> trusted-key operations.
> >>
> >> Fixes: 240730437deb ("KEYS: trusted: explicitly use tpm_chip structure...")
> >> Cc: Roberto Sassu <roberto.sassu@...wei.com>
> >> Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> >> Cc: James Bottomley <jejb@...ux.ibm.com>
> >> Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> >> Cc: Mimi Zohar <zohar@...ux.ibm.com>
> >> Cc: David Howells <dhowells@...hat.com>
> >> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> >
> > It should check for chip in each function that uses TPM now that
> > the code does not rely on default chip. Otherwise, the semantics
> > are kind of inconsistent.
>
> If no other TPM function can be used before a successful key
> instantiate, checking for a chip only in trusted_instantiate() seems
> sufficient. Then, the same chip will be used by all TPM functions until
> module unloading, since we incremented the reference count.
>
> I would suggest to move the tpm_default_chip() and init_digests() calls
> to trusted_instantiate() to restore the old behavior of init_trusted().
>
> trusted_instantiate() should look like:
> ---
> if (!chip) {
>         chip = tpm_default_chip();
>         if (!chip)
>                 return -ENODEV;
> }
>
> if (!digests) {
>         ret = init_digests();
>         if (ret < 0)
>                 return ret;
> }

This patch already achieves that because tpm_find_get_ops() will fail
and cause tpm_is_tpm2() to return NULL.