linux-kernel - Re: [PATCH v2] KEYS: trusted: allow module init if TPM is inactive or deactivated

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Date:   Fri, 2 Aug 2019 11:15:28 -0500
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     jarkko.sakkinen@...ux.intel.com, 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,
        nayna@...ux.vnet.ibm.com, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v2] KEYS: trusted: allow module init if TPM is inactive
 or deactivated

On 2019-08-02 18:11:09, Roberto Sassu wrote:
> On 8/2/2019 5:34 PM, Roberto Sassu wrote:
> > On 8/2/2019 5:30 PM, Tyler Hicks wrote:
> > > On 2019-08-02 17:07:33, 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
> > >                                                     ^ if
> > > 
> > > > avoid module dependency problems.
> > > > 
> > > > However, trusted module initialization can still fail if the TPM is
> > > > inactive or deactivated. This patch ignores tpm_get_random() errors in
> > > > init_digests() and returns -EFAULT in pcrlock() if the TPM didn't return
> > > > random data.
> > > > 
> > > > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > > 
> > > The code changes look correct to me.
> > > 
> > >    Reviewed-by: Tyler Hicks <tyhicks@...onical.com>
> > > 
> > > For whoever takes this patch through their tree, I think that adding the
> > > following Fixes tag would be useful (as well as cc'ing stable):
> > > 
> > >    Fixes: 240730437deb ("KEYS: trusted: explicitly use tpm_chip
> > > structure...")
> > > 
> > > I think it is also worth leaving a short note, in the commit message,
> > > for backporters that commit 782779b60faa ("tpm: Actually fail on TPM
> > > errors during "get random"") should be included with any backports of
> > > this patch.
> > 
> > Right, thanks. I wait for Jarkko's comments and I add both the Fixes tag
> > and the short note in the next version of the patch.
> 
> Uhm, I was thinking that maybe it is not necessary to mention commit
> 782779b60faa. This patch would still return 0 even if that commit is not
> backported (TPM_ERR_DISABLED < TPM_MAX_DIGEST_SIZE).

The commit message for 782779b60faa shows 379 being returned when
attempting to get random:

  [   18.092103] tpm tpm0: A TPM error (379) occurred attempting get random

I don't know enough about TPM chips to know how common that is...

Tyler

> 
> Roberto
> 
> -- 
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