linux-kernel - Re: [tpmdd-devel] [PATCH v6 3/3] tpm: vtpm_proxy: Prevent userspace from sending driver command

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Message-ID: <20170525001049.4e2zyxeihs3cvq2n@intel.com>
Date:   Wed, 24 May 2017 17:10:49 -0700
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH v6 3/3] tpm: vtpm_proxy: Prevent userspace
 from sending driver command

On Wed, May 24, 2017 at 03:22:11PM -0700, Jarkko Sakkinen wrote:
> On Wed, May 24, 2017 at 05:39:41PM -0400, Stefan Berger wrote:
> > To prevent userspace from sending the TPM driver command to set
> > the locality, we need to check every command that is sent from
> > user space. To distinguish user space commands from internally
> > sent commands we introduce an additional state flag
> > STATE_DRIVER_COMMAND that is set while the driver sends this
> > command. Similar to the TPM 2 space commands we return an error
> > code when this command is detected.
> > 
> > Signed-off-by: Stefan Berger <stefanb@...ux.vnet.ibm.com>
> > ---
> >  drivers/char/tpm/tpm_vtpm_proxy.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> > 
> > diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
> > index 66024bf..1d877cc 100644
> > --- a/drivers/char/tpm/tpm_vtpm_proxy.c
> > +++ b/drivers/char/tpm/tpm_vtpm_proxy.c
> > @@ -43,6 +43,7 @@ struct proxy_dev {
> >  #define STATE_OPENED_FLAG        BIT(0)
> >  #define STATE_WAIT_RESPONSE_FLAG BIT(1)  /* waiting for emulator response */
> >  #define STATE_REGISTERED_FLAG	 BIT(2)
> > +#define STATE_DRIVER_COMMAND     BIT(3)  /* sending a driver specific command */
> >  
> >  	size_t req_len;              /* length of queued TPM request */
> >  	size_t resp_len;             /* length of queued TPM response */
> > @@ -299,6 +300,28 @@ static int vtpm_proxy_tpm_op_recv(struct tpm_chip *chip, u8 *buf, size_t count)
> >  	return len;
> >  }
> >  
> > +static int vtpm_proxy_is_driver_command(struct tpm_chip *chip,
> > +					u8 *buf, size_t count)
> > +{
> > +	struct tpm_input_header *hdr = (struct tpm_input_header *)buf;
> > +
> > +	if (count < sizeof(struct tpm_input_header))
> > +		return 0;
> > +
> > +	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> > +		switch (be32_to_cpu(hdr->ordinal)) {
> > +		case TPM2_CC_SET_LOCALITY:
> > +			return 1;
> > +		}
> > +	} else {
> > +		switch (be32_to_cpu(hdr->ordinal)) {
> > +		case TPM_ORD_SET_LOCALITY:
> > +			return 1;
> > +		}
> > +	}
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Called when core TPM driver forwards TPM requests to 'server side'.
> >   *
> > @@ -321,6 +344,10 @@ static int vtpm_proxy_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t count)
> >  		return -EIO;
> >  	}
> >  
> > +	if (!(proxy_dev->state & STATE_DRIVER_COMMAND) &&
> > +	    vtpm_proxy_is_driver_command(chip, buf, count))
> > +		return -EFAULT;
> > +
> >  	mutex_lock(&proxy_dev->buf_lock);
> >  
> >  	if (!(proxy_dev->state & STATE_OPENED_FLAG)) {
> > @@ -376,6 +403,7 @@ static int vtpm_proxy_request_locality(struct tpm_chip *chip, int locality)
> >  	struct tpm_buf buf;
> >  	int rc;
> >  	const struct tpm_output_header *header;
> > +	struct proxy_dev *proxy_dev = dev_get_drvdata(&chip->dev);
> >  
> >  	if (chip->flags & TPM_CHIP_FLAG_TPM2)
> >  		rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS,
> > @@ -387,9 +415,14 @@ static int vtpm_proxy_request_locality(struct tpm_chip *chip, int locality)
> >  		return rc;
> >  	tpm_buf_append_u8(&buf, locality);
> >  
> > +	proxy_dev->state |= STATE_DRIVER_COMMAND;
> > +
> >  	rc = tpm_transmit_cmd(chip, NULL, buf.data, tpm_buf_length(&buf), 0,
> >  			      TPM_TRANSMIT_UNLOCKED | TPM_TRANSMIT_RAW,
> >  			      "attempting to set locality");
> > +
> > +	proxy_dev->state &= ~STATE_DRIVER_COMMAND;
> > +
> >  	if (rc < 0) {
> >  		locality = rc;
> >  		goto out;
> > -- 
> > 2.4.3
> > 
> 
> Otherwise fine except for the redundant code.
> 
> /Jarkko

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

Probably not yet merging and testing this this week though as I'm
travelling in US right now.

/Jarkko