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

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Date:   Fri, 22 Mar 2019 12:12:27 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     Dan Williams <dan.j.williams@...el.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>,
        Silviu Vlasceanu <Silviu.Vlasceanu@...wei.com>
Subject: Re: [PATCH] security/keys/trusted: Allow operation without hardware
 TPM

On Thu, Mar 21, 2019 at 06:45:47PM +0100, Roberto Sassu wrote:
> On 3/21/2019 5:30 PM, Dan Williams wrote:
> > 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.
> 
> In addition, the changes I proposed would allow users to create trusted
> keys if a TPM is added later. CONFIG_TRUSTED_KEYS=y and
> CONFIG_TCG_TPM=m is a valid configuration.
> 
> Jarkko, Dan's patch seems sufficient to fix the issue. He could include
> the changes I proposed in his patch. What is your opinion?

Agreed.

/Jarkko