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

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Date:   Thu, 21 Mar 2019 18:45:47 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     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 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?

Thanks

Roberto

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