[PATCH] tpm: remove file header documentation from tpm2-sessions.c

Jarkko Sakkinen
2024-09-15T12:33:31Z

The documentation in the file header is duplicate documentation, which
is already addressed elsewhere (tpm-security.rs and function associated
documentations). In addition remove the invalid newline character after
the SPDX tag.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
It is good time to remove this finally before doing anything else.
Unless someone commits to maintain this part of the file, I will just
take it away because I have neither intention nor motivation to maintain
it. Came right on front when I started to look into kernel command-line
and optimizations for session life-time so thus the patch. I'll include
this later on to a larger patch set.
drivers/char/tpm/tpm2-sessions.c | 65 --------------------------------
1 file changed, 65 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 44f60730cff4..6cc1ea81c57c 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -1,71 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
-
/*
* Copyright (C) 2018 James.Bottomley@HansenPartnership.com
- *
- * Cryptographic helper routines for handling TPM2 sessions for
- * authorization HMAC and request response encryption.
- *
- * The idea is to ensure that every TPM command is HMAC protected by a
- * session, meaning in-flight tampering would be detected and in
- * addition all sensitive inputs and responses should be encrypted.
- *
- * The basic way this works is to use a TPM feature called salted
- * sessions where a random secret used in session construction is
- * encrypted to the public part of a known TPM key. The problem is we
- * have no known keys, so initially a primary Elliptic Curve key is
- * derived from the NULL seed (we use EC because most TPMs generate
- * these keys much faster than RSA ones). The curve used is NIST_P256
- * because that's now mandated to be present in 'TCG TPM v2.0
- * Provisioning Guidance'
- *
- * Threat problems: the initial TPM2_CreatePrimary is not (and cannot
- * be) session protected, so a clever Man in the Middle could return a
- * public key they control to this command and from there intercept
- * and decode all subsequent session based transactions. The kernel
- * cannot mitigate this threat but, after boot, userspace can get
- * proof this has not happened by asking the TPM to certify the NULL
- * key. This certification would chain back to the TPM Endorsement
- * Certificate and prove the NULL seed primary had not been tampered
- * with and thus all sessions must have been cryptographically secure.
- * To assist with this, the initial NULL seed public key name is made
- * available in a sysfs file.
- *
- * Use of these functions:
- *
- * The design is all the crypto, hash and hmac gunk is confined in this
- * file and never needs to be seen even by the kernel internal user. To
- * the user there's an init function tpm2_sessions_init() that needs to
- * be called once per TPM which generates the NULL seed primary key.
- *
- * 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
- * error legs where the latter is not executed.
- * tpm_buf_append_name() to add a handle to the buffer. This must be
- * used in place of the usual tpm_buf_append_u32() for adding
- * handles because handles have to be processed specially when
- * calculating the HMAC. In particular, for NV, volatile and
- * permanent objects you now need to provide the name.
- * tpm_buf_append_hmac_session() which appends the hmac session to the
- * buf in the same way tpm_buf_append_auth does().
- * tpm_buf_fill_hmac_session() This calculates the correct hash and
- * places it in the buffer. It must be called after the complete
- * command buffer is finalized so it can fill in the correct HMAC
- * based on the parameters.
- * tpm_buf_check_hmac_response() which checks the session response in
- * the buffer and calculates what it should be. If there's a
- * mismatch it will log a warning and return an error. If
- * tpm_buf_append_hmac_session() did not specify
- * TPM_SA_CONTINUE_SESSION then the session will be closed (if it
- * hasn't been consumed) and the auth structure freed.
*/

#include "tpm.h"
--
2.46.0