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

Jarkko Sakkinen
2017-01-29T21:40:09Z

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@HansenPartnership.com>
>
> ---
>
> 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