Re: [PATCH 6/6] tpm2: add session handle context saving and restoring to the space code

[Jarkko Sakkinen]

On Wed, Feb 08, 2017 at 01:07:08PM +0200, Jarkko Sakkinen wrote:
> From: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> 
> Sessions are different from transient objects in that their handles
> may not be virtualized (because they're used for some hmac
> calculations).  Additionally when a session is context saved, a
> vestigial memory remains in the TPM and if it is also flushed, that
> will be lost and the session context will refuse to load next time, so
> the code is updated to flush only transient objects after a context
> save.  Add a separate array (chip->session_tbl) to save and restore
> sessions by handle.  Use the failure of a context save or load to
> signal that the session has been flushed from the TPM and we can
> remove its memory from chip->session_tbl.
> 
> Sessions are also isolated during each instance of a tpm space.  This
> means that spaces shouldn't be able to see each other's sessions and
> is enforced by ensuring that a space user may only refer to sessions
> handles that are present in their own chip->session_tbl.  Finally when
> a space is closed, all the sessions belonging to it should be flushed
> so the handles may be re-used by other spaces.
> 
> Note that if we get a session save or load error, all sessions are
> effectively flushed.  Even though we restore the session buffer, all
> the old sessions will refuse to load after the flush and they'll be
> purged from our session memory.  This means that while transient
> context handling is still soft in the face of errors, session handling
> is hard (any failure of the model means all sessions are lost).
> 
> Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/char/tpm/tpm-chip.c   |   6 +++
>  drivers/char/tpm/tpm.h        |   4 +-
>  drivers/char/tpm/tpm2-space.c | 115 ++++++++++++++++++++++++++++++++++++++++--
>  drivers/char/tpm/tpms-dev.c   |   2 +-
>  4 files changed, 122 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index c71c353..e8536ab 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -130,6 +130,7 @@ static void tpm_dev_release(struct device *dev)
>  
>  	kfree(chip->log.bios_event_log);
>  	kfree(chip->work_space.context_buf);
> +	kfree(chip->work_space.session_buf);
>  	kfree(chip);
>  }
>  
> @@ -224,6 +225,11 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>  		rc = -ENOMEM;
>  		goto out;
>  	}
> +	chip->work_space.session_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (!chip->work_space.session_buf) {
> +		rc = -ENOMEM;
> +		goto out;
> +	}
>  
>  	return chip;
>  
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 8670cc5..9261223 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -160,6 +160,8 @@ enum tpm2_cc_attrs {
>  struct tpm_space {
>  	u32 context_tbl[3];
>  	u8 *context_buf;
> +	u32 session_tbl[3];
> +	u8 *session_buf;
>  };
>  
>  enum tpm_chip_flags {
> @@ -588,7 +590,7 @@ int tpm2_probe(struct tpm_chip *chip);
>  ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip);
>  int tpm2_find_cc(struct tpm_chip *chip, u32 cc);
>  int tpm2_init_space(struct tpm_space *space);
> -void tpm2_del_space(struct tpm_space *space);
> +void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space);
>  int tpm2_prepare_space(struct tpm_chip *chip, struct tpm_space *space, u32 cc,
>  		       u8 *cmd);
>  int tpm2_commit_space(struct tpm_chip *chip, struct tpm_space *space,
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index d241c2a..fb817ca 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -32,18 +32,39 @@ struct tpm2_context {
>  	__be16 blob_size;
>  } __packed;
>  
> +static void tpm2_flush_sessions(struct tpm_chip *chip, struct tpm_space *space)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(space->session_tbl); i++) {
> +		if (space->session_tbl[i])
> +			tpm2_flush_context_cmd(chip, space->session_tbl[i],
> +					       TPM_TRANSMIT_UNLOCKED);
> +	}
> +}
> +
>  int tpm2_init_space(struct tpm_space *space)
>  {
>  	space->context_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
>  	if (!space->context_buf)
>  		return -ENOMEM;
>  
> +	space->session_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (space->session_buf == NULL) {
> +		kfree(space->context_buf);
> +		return -ENOMEM;
> +	}
> +
>  	return 0;
>  }
>  
> -void tpm2_del_space(struct tpm_space *space)
> +void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space)
>  {
> +	mutex_lock(&chip->tpm_mutex);
> +	tpm2_flush_sessions(chip, space);
> +	mutex_unlock(&chip->tpm_mutex);
>  	kfree(space->context_buf);
> +	kfree(space->session_buf);
>  }
>  
>  static int tpm2_load_context(struct tpm_chip *chip, u8 *buf,
> @@ -69,6 +90,20 @@ static int tpm2_load_context(struct tpm_chip *chip, u8 *buf,
>  			 __func__, rc);
>  		tpm_buf_destroy(&tbuf);
>  		return -EFAULT;
> +	} else if (tpm2_rc_value(rc) == TPM2_RC_HANDLE ||
> +		   rc == TPM2_RC_REFERENCE_H0) {
> +		/*
> +		 * TPM_RC_HANDLE means that the session context can't
> +		 * be loaded because of an internal counter mismatch
> +		 * that makes the TPM think there might have been a
> +		 * replay.  This might happen if the context was saved
> +		 * and loaded outside the space.
> +		 *
> +		 * TPM_RC_REFERENCE_H0 means the session has been
> +		 * flushed outside the space
> +		 */
> +		rc = -ENOENT;
> +		tpm_buf_destroy(&tbuf);
>  	} else if (rc > 0) {
>  		dev_warn(&chip->dev, "%s: failed with a TPM error 0x%04X\n",
>  			 __func__, rc);
> @@ -121,12 +156,30 @@ static int tpm2_save_context(struct tpm_chip *chip, u32 handle, u8 *buf,
>  	}
>  
>  	memcpy(&buf[*offset], &tbuf.data[TPM_HEADER_SIZE], body_size);
> -	tpm2_flush_context_cmd(chip, handle, TPM_TRANSMIT_UNLOCKED);
>  	*offset += body_size;
>  	tpm_buf_destroy(&tbuf);
>  	return 0;
>  }
>  
> +static int tpm2_session_add(struct tpm_chip *chip, u32 handle)
> +{
> +	struct tpm_space *space = &chip->work_space;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(space->session_tbl); i++)
> +		if (space->session_tbl[i] == 0)
> +			break;
> +	if (i == ARRAY_SIZE(space->session_tbl)) {
> +		dev_err(&chip->dev, "out of session slots\n");

This really should be dev_dbg.

/Jarkko