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

[Roberto Sassu]

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;
}
---

Roberto


> /Jarkko

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