Re: [PATCH v4] tpm: Mask TPM RC in tpm2_start_auth_session()

On Mon, Apr 07, 2025 at 03:28:05PM +0300, Jarkko Sakkinen wrote:

tpm2_start_auth_session() does not mask TPM RC correctly from the callers:

[ 28.766528] tpm tpm0: A TPM error (2307) occurred start auth session

Process TPM RCs inside tpm2_start_auth_session(), and map them to POSIX error codes.

Cc: stable@vger.kernel.org # v6.10+ Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions") Reported-by: Herbert Xu herbert@gondor.apana.org.au Closes: https://lore.kernel.org/linux-integrity/Z_NgdRHuTKP6JK--@gondor.apana.org.au... Signed-off-by: Jarkko Sakkinen jarkko@kernel.org

---

v4:

• tpm_to_ret()

v3:

• rc > 0

v2:

• Investigate TPM rc only after destroying tpm_buf.

---

drivers/char/tpm/tpm2-sessions.c | 20 ++++++-------------- include/linux/tpm.h | 21 +++++++++++++++++++++ 2 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c index 3f89635ba5e8..102e099f22c1 100644 --- a/drivers/char/tpm/tpm2-sessions.c +++ b/drivers/char/tpm/tpm2-sessions.c @@ -40,11 +40,6 @@

• These are the usage functions:

• • tpm2_start_auth_session() which allocates the opaque auth structure
• • and gets a session from the TPM. This must be called before
• • any of the following functions. The session is protected by a
• • session_key which is derived from a random salt value
• • encrypted to the NULL seed.
  • tpm2_end_auth_session() kills the session and frees the resources.
  • Under normal operation this function is done by
  • tpm_buf_check_hmac_response(), so this is only to be used on

@@ -963,16 +958,13 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key) } /**

• • tpm2_start_auth_session() - create a HMAC authentication session with the TPM
• • @chip: the TPM chip structure to create the session with

• • tpm2_start_auth_session() - Create an a HMAC authentication session
• • @chip: A TPM chip

• • This function loads the NULL seed from its saved context and starts
• • an authentication session on the null seed, fills in the
• • @chip->auth structure to contain all the session details necessary
• • for performing the HMAC, encrypt and decrypt operations and
• • returns. The NULL seed is flushed before this function returns.

• • Loads the ephemeral key (null seed), and starts an HMAC authenticated
• • session. The null seed is flushed before the return.

• • Return: zero on success or actual error encountered.

• • Returns zero on success, or a POSIX error code.
  */

int tpm2_start_auth_session(struct tpm_chip *chip) { @@ -1024,7 +1016,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip) /* hash algorithm for session */ tpm_buf_append_u16(&buf, TPM_ALG_SHA256);

• rc = tpm_transmit_cmd(chip, &buf, 0, "start auth session");

• rc = tpm_to_ret(tpm_transmit_cmd(chip, &buf, 0, "StartAuthSession"));

The cool thing here is that e.g., in the case of tpm2_start_auth_session, there is two implementation options:

1. tpm_to_ret(tpm2_start_auth_session) 2. tpm_to_ret(tpm_transmit_cmd)

Just want to expose this choice..

tpm2_flush_context(chip, null_key); if (rc == TPM2_RC_SUCCESS) diff --git a/include/linux/tpm.h b/include/linux/tpm.h index 6c3125300c00..c826d5a9d894 100644 --- a/include/linux/tpm.h +++ b/include/linux/tpm.h @@ -257,8 +257,29 @@ enum tpm2_return_codes { TPM2_RC_TESTING = 0x090A, /* RC_WARN */ TPM2_RC_REFERENCE_H0 = 0x0910, TPM2_RC_RETRY = 0x0922,

• TPM2_RC_SESSION_MEMORY = 0x0903,

}; +/*

• • Convert a return value from tpm_transmit_cmd() to a POSIX return value. The
• • fallback return value is -EFAULT.
• */

+static inline ssize_t tpm_to_ret(ssize_t ret) +{

• /* Already a POSIX error: */
• if (ret < 0)

• return ret;
  

• switch (ret) {
• case TPM2_RC_SUCCESS:

• return 0;
  

• case TPM2_RC_SESSION_MEMORY:

• return -ENOMEM;
  

• default:

• return -EFAULT;
  

• }

+}

enum tpm2_command_codes { TPM2_CC_FIRST = 0x011F, TPM2_CC_HIERARCHY_CONTROL = 0x0121, -- 2.39.5

BR, Jarkko