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

[Roberto Sassu]

On 3/21/2019 5:30 PM, Dan Williams wrote:
> On Thu, Mar 21, 2019 at 7:27 AM Roberto Sassu <roberto.sassu@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > Cc: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > > > Cc: James Bottomley <jejb@xxxxxxxxxxxxx>
> > > > Cc: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > > > Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > > > Cc: David Howells <dhowells@xxxxxxxxxx>
> > > > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > >
> > > 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?

Thanks

Roberto

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