linux-kernel - Re: [PATCH v5 14/17] tpm: remove TPM_TRANSMIT

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Date:   Thu, 8 Nov 2018 21:02:34 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Tadeusz Struk <tadeusz.struk@...el.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 14/17] tpm: remove TPM_TRANSMIT_UNLOCKED flag

On Thu, Nov 08, 2018 at 10:43:46AM -0500, Stefan Berger wrote:
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index f2b0e5c52a57..d6abc964ef66 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -652,17 +652,12 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
> >   	u32 blob_handle;
> >   	int rc;
> > 
> > -	mutex_lock(&chip->tpm_mutex);
> > -	rc = tpm2_load_cmd(chip, payload, options, &blob_handle,
> > -			   TPM_TRANSMIT_UNLOCKED);
> > +	rc = tpm2_load_cmd(chip, payload, options, &blob_handle, 0);
> >   	if (rc)
> > -		goto out;
> > +		return rc;
> > 
> > -	rc = tpm2_unseal_cmd(chip, payload, options, blob_handle,
> > -			     TPM_TRANSMIT_UNLOCKED);
> > -	tpm2_flush_context_cmd(chip, blob_handle, TPM_TRANSMIT_UNLOCKED);
> > -out:
> > -	mutex_unlock(&chip->tpm_mutex);
> > +	rc = tpm2_unseal_cmd(chip, payload, options, blob_handle, 0);
> > +	tpm2_flush_context_cmd(chip, blob_handle, 0);
> 
> 
> This lock was covering quite a few commands from being interfered by others.
> Is this still guaranteed to work after or can different subsystems like
> trusted keys and IMA and /dev/tpm0 users interfere with this previous atomic
> sequence ?

One way to keep this sequence atomic would be to use a TPM space. Then
you can release the lock in-between the sequence.

/Jarkko