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Message-ID: <e7ul3n3rwvv3xiyiaf4dv5x7kbtcgb6zpcf33k6dobxf5ctdyp@z5iwi4pofj7h>
Date: Mon, 7 Apr 2025 15:51:21 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: keyrings@...r.kernel.org, stable@...r.kernel.org,
Herbert Xu <herbert@...dor.apana.org.au>, David Howells <dhowells@...hat.com>,
Lukas Wunner <lukas@...ner.de>, Ignat Korchagin <ignat@...udflare.com>,
"David S. Miller" <davem@...emloft.net>, Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
James Bottomley <James.Bottomley@...senpartnership.com>, Ard Biesheuvel <ardb@...nel.org>, linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org
Subject: 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@...r.kernel.org # v6.10+
>Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
>Reported-by: Herbert Xu <herbert@...dor.apana.org.au>
>Closes: https://lore.kernel.org/linux-integrity/Z_NgdRHuTKP6JK--@gondor.apana.org.au/
>Signed-off-by: Jarkko Sakkinen <jarkko@...nel.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"));
> 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,
nit: the other values are in ascending order, should we keep it or is it
not important?
(more a question for me than for the patch)
> };
>
>+/*
>+ * 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;
>+ }
>+}
I like this and in the future we could reuse it in different places like
tpm2_load_context() and tpm2_save_context().
Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>
BTW for my understading, looking at that code (sorry if the answer is
obvious, but I'm learning) I'm confused about the use of
tpm2_rc_value().
For example in tpm2_load_context() we have:
rc = tpm_transmit_cmd(chip, &tbuf, 4, NULL);
...
} else if (tpm2_rc_value(rc) == TPM2_RC_HANDLE ||
rc == TPM2_RC_REFERENCE_H0) {
While in tpm2_save_context(), we have:
rc = tpm_transmit_cmd(chip, &tbuf, 0, NULL);
...
} else if (tpm2_rc_value(rc) == TPM2_RC_REFERENCE_H0) {
So to check TPM2_RC_REFERENCE_H0 we are using tpm2_rc_value() only
sometimes, what's the reason?
Thanks,
Stefano
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