On Mon, Jan 23, 2017 at 09:37:11PM -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.
>
> Signed-off-by: James Bottomley <james.bottom...@hansenpartnership.com>
I'm wondering if you ever need more than two sessions at once? If we
would limit the number of sessions to that you could probably simplify a
lot.
> ---
> drivers/char/tpm/tpm-chip.c | 6 +++
> drivers/char/tpm/tpm.h | 3 ++
> drivers/char/tpm/tpm2-space.c | 99
> +++++++++++++++++++++++++++++++++++++++----
> drivers/char/tpm/tpms-dev.c | 8 ++++
> 4 files changed, 107 insertions(+), 9 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 c48255e..b77fc60 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -159,6 +159,8 @@ enum tpm2_cc_attrs {
> struct tpm_space {
> u32 context_tbl[3];
> u8 *context_buf;
> + u32 session_tbl[6];
> + u8 *session_buf;
> };
>
> enum tpm_chip_flags {
> @@ -588,4 +590,5 @@ 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,
> u32 cc, u8 *buf, size_t bufsiz);
> +void tpm2_flush_space(struct tpm_chip *chip, struct tpm_space *space);
Why the extra parameter?
> #endif
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index 7fd2fc5..ba4310a 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -59,11 +59,16 @@ static int tpm2_load_context(struct tpm_chip *chip, u8
> *buf,
>
> rc = tpm_transmit_cmd(chip, NULL, tbuf.data, PAGE_SIZE, 4,
> TPM_TRANSMIT_UNLOCKED, NULL);
> +
cruft
> if (rc < 0) {
> dev_warn(&chip->dev, "%s: failed with a system error %d\n",
> __func__, rc);
> tpm_buf_destroy(&tbuf);
> return -EFAULT;
> + } else if ((rc & TPM2_RC_HANDLE) == TPM2_RC_HANDLE ||
> + rc == TPM2_RC_REFERENCE_H0) {
> + 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);
> @@ -116,21 +121,44 @@ 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 void tpm2_flush_space(struct tpm_chip *chip)
> +static int tpm2_session_add(struct tpm_chip *chip,
> + struct tpm_space *space, u32 handle)
> +{
> + 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");
> + tpm2_flush_context_cmd(chip, handle, TPM_TRANSMIT_UNLOCKED);
> + return -ENOMEM;
> + }
> +
> + space->session_tbl[i] = handle;
> +
> + return 0;
> +}
> +
> +void tpm2_flush_space(struct tpm_chip *chip, struct tpm_space *space)
> {
> - struct tpm_space *space = &chip->work_space;
> int i;
>
> for (i = 0; i < ARRAY_SIZE(space->context_tbl); i++)
> if (space->context_tbl[i] && ~space->context_tbl[i])
> tpm2_flush_context_cmd(chip, space->context_tbl[i],
> TPM_TRANSMIT_UNLOCKED);
> +
> + 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);
> + }
> }
>
> static int tpm2_load_space(struct tpm_chip *chip)
> @@ -156,6 +184,28 @@ static int tpm2_load_space(struct tpm_chip *chip)
> return rc;
> }
>
> + for (i = 0, offset = 0; i < ARRAY_SIZE(space->session_tbl); i++) {
> + u32 handle;
> +
> + if (!space->session_tbl[i])
> + continue;
> +
> + rc = tpm2_load_context(chip, space->session_buf,
> + &offset, &handle);
> + if (rc == -ENOENT) {
> + /* load failed, just forget session */
> + space->session_tbl[i] = 0;
> + } else if (rc) {
> + tpm2_flush_space(chip, space);
> + return rc;
> + }
> + if (handle != space->session_tbl[i]) {
> + dev_warn(&chip->dev, "session restored to wrong
> handle\n");
> + tpm2_flush_space(chip, space);
> + return -EFAULT;
> + }
> + }
> +
> return 0;
> }
>
> @@ -215,17 +265,20 @@ int tpm2_prepare_space(struct tpm_chip *chip, struct
> tpm_space *space, u32 cc,
>
> memcpy(&chip->work_space.context_tbl, &space->context_tbl,
> sizeof(space->context_tbl));
> + memcpy(&chip->work_space.session_tbl, &space->session_tbl,
> + sizeof(space->session_tbl));
> memcpy(chip->work_space.context_buf, space->context_buf, PAGE_SIZE);
> + memcpy(chip->work_space.session_buf, space->session_buf, PAGE_SIZE);
For transient objects the rollback is straight forward and totally
predictable. Given that with sessions you always keep some information
in the TPM the rollback would be a bit more complicated.
Now your code seems to just keep the previous session_buf, doesn't it?
Does that always work or not?
PS. I have a high-level idea of attack vectors that are prevented by
having meta-data for session inside the TPM but can you point me to
the correct place in the TPM 2.0 specification that discusses about
this?
/Jarkko
