linux-kernel - [PATCH v3 6/7] tpm: flush the auth session only when /dev/tpm0 is open

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Message-ID: <20240917154444.702370-7-jarkko@kernel.org>
Date: Tue, 17 Sep 2024 18:44:35 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: linux-integrity@...r.kernel.org
Cc: James.Bottomley@...senPartnership.com,
	roberto.sassu@...wei.com,
	mapengyu@...il.com,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	keyrings@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 6/7] tpm: flush the auth session only when /dev/tpm0 is open

Instead of flushing and reloading the auth session for every single
transaction, keep the session open unless /dev/tpm0 is used. In practice
this means applying TPM2_SA_CONTINUE_SESSION to the session attributes.
Flush the session always when /dev/tpm0 is written.

This reduces the number of TPM2_ContextLoad and TPM2_FlushContext
commands

Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
v3:
- Refined the commit message.
- Removed the conditional for applying TPM2_SA_CONTINUE_SESSION only when
  /dev/tpm0 is open. It is not required as the auth session is flushed,
  not saved.
v2:
- A new patch.
---
 drivers/char/tpm/tpm-chip.c       | 1 +
 drivers/char/tpm/tpm-dev-common.c | 1 +
 drivers/char/tpm/tpm-interface.c  | 1 +
 drivers/char/tpm/tpm2-sessions.c  | 3 +++
 4 files changed, 6 insertions(+)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 0ea00e32f575..7a6bb30d1f32 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -680,6 +680,7 @@ void tpm_chip_unregister(struct tpm_chip *chip)
 	rc = tpm_try_get_ops(chip);
 	if (!rc) {
 		if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+			tpm2_end_auth_session(chip);
 			tpm2_flush_context(chip, chip->null_key);
 			chip->null_key = 0;
 		}
diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
index 4bc07963e260..c6fdeb4feaef 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -29,6 +29,7 @@ static ssize_t tpm_dev_transmit(struct tpm_chip *chip, struct tpm_space *space,
 
 #ifdef CONFIG_TCG_TPM2_HMAC
 	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+		tpm2_end_auth_session(chip);
 		tpm2_flush_context(chip, chip->null_key);
 		chip->null_key = 0;
 	}
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index bfa47d48b0f2..2363018fa8fb 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -381,6 +381,7 @@ int tpm_pm_suspend(struct device *dev)
 	if (!rc) {
 		if (chip->flags & TPM_CHIP_FLAG_TPM2) {
 #ifdef CONFIG_TCG_TPM2_HMAC
+			tpm2_end_auth_session(chip);
 			tpm2_flush_context(chip, chip->null_key);
 			chip->null_key = 0;
 #endif
diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 43b8e3576232..d240039d0849 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -268,6 +268,9 @@ void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
 	}
 
 #ifdef CONFIG_TCG_TPM2_HMAC
+	/* The first write to /dev/tpm{rm0} will flush the session. */
+	attributes |= TPM2_SA_CONTINUE_SESSION;
+
 	/*
 	 * The Architecture Guide requires us to strip trailing zeros
 	 * before computing the HMAC
-- 
2.46.0