linux-kernel - Re: [PATCH] KEYS: trusted: allow module init if TPM is inactive or deactivated

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Date:   Mon, 15 Jul 2019 18:44:28 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     <jejb@...ux.ibm.com>, <zohar@...ux.ibm.com>, <jgg@...pe.ca>,
        <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <keyrings@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <crazyt2019+lml@...il.com>, <tyhicks@...onical.com>,
        <nayna@...ux.vnet.ibm.com>, <silviu.vlasceanu@...wei.com>
Subject: Re: [PATCH] KEYS: trusted: allow module init if TPM is inactive or
 deactivated

On 7/11/2019 9:48 PM, Jarkko Sakkinen wrote:
> On Fri, Jul 05, 2019 at 06:37:35PM +0200, Roberto Sassu wrote:
>> Commit c78719203fc6 ("KEYS: trusted: allow trusted.ko to initialize w/o a
>> TPM") allows the trusted module to be loaded even a TPM is not found to
>> avoid module dependency problems.
>>
>> Unfortunately, this does not completely solve the issue, as there could be
>> a case where a TPM is found but is not functional (the TPM commands return
>> an error). Specifically, after the tpm_chip structure is returned by
>> tpm_default_chip() in init_trusted(), the execution terminates after
>> init_digests() returns -EFAULT (due to the fact that tpm_get_random()
>> returns a positive value, but less than TPM_MAX_DIGEST_SIZE).
>>
>> This patch fixes the issue by ignoring the TPM_ERR_DEACTIVATED and
>> TPM_ERR_DISABLED errors.
> 
> Why allow trusted module to initialize if TPM is not functional?

According to the bug report at https://bugs.archlinux.org/task/62678,
the trusted module is a dependency of the ecryptfs module. We should
load the trusted module even if the TPM is inactive or deactivated.

Given that commit 782779b60faa ("tpm: Actually fail on TPM errors during
"get random"") changes the return code of tpm_get_random(), the patch
should be modified to ignore the -EIO error. I will send a new version.

Roberto

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