Re: [tpmdd-devel] [PATCH v2 1/2] tpm2: add session handle context saving and restoring to the space code

[Jarkko Sakkinen]

On Fri, Jan 27, 2017 at 04:32:38PM -0800, James Bottomley wrote:
> 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>
> 
> ---
> 
> v2: - add kill space to remove sessions on close
>     - update changelog
>     - reduce session table to 3 entries
> ---
>  drivers/char/tpm/tpm-chip.c   |   6 +++
>  drivers/char/tpm/tpm.h        |   4 +-
>  drivers/char/tpm/tpm2-space.c | 112 ++++++++++++++++++++++++++++++++++++++++--
>  drivers/char/tpm/tpms-dev.c   |   2 +-
>  4 files changed, 118 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index ed4f887..6282ad0 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);
>  }
>  
> @@ -223,6 +224,11 @@ 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 c4b8ec9..10c57b9 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -161,6 +161,8 @@ 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 {
> @@ -583,7 +585,7 @@ unsigned long tpm2_calc_ordinal_duration(struct tpm_chip *chip, u32 ordinal);
>  int tpm2_probe(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..2b3d1ad 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -32,18 +32,28 @@ struct tpm2_context {
>  	__be16 blob_size;
>  } __packed;
>  
> +static void tpm2_kill_sessions(struct tpm_chip *chip, struct tpm_space *space);
> +
>  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)
>  {
> +	tpm2_kill_sessions(chip, space);
>  	kfree(space->context_buf);
> +	kfree(space->session_buf);
>  }
>  
>  static int tpm2_load_context(struct tpm_chip *chip, u8 *buf,
> @@ -69,6 +79,10 @@ 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) {
> +		rc = -ENOENT;
> +		tpm_buf_destroy(&tbuf);

1. Why isn't the check in tpm2_save_context sufficient to know that
   session was flushed?
2. Can it really return both TPM_RC_HANDLE and TPM_RC_REFERENCE_H0? 

/Jarkko