linux-kernel - [PATCH v10 3/4] tpm, tpm2-cmd: Use stack for trivial cases

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Message-Id: <20250921020804.1088824-4-jarkko@kernel.org>
Date: Sun, 21 Sep 2025 05:08:03 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: linux-integrity@...r.kernel.org
Cc: Stefano Garzarella <sgarzare@...hat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
	Peter Huewe <peterhuewe@....de>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	linux-kernel@...r.kernel.org (open list),
	keyrings@...r.kernel.org (open list:KEYS/KEYRINGS),
	linux-security-module@...r.kernel.org (open list:SECURITY SUBSYSTEM)
Subject: [PATCH v10 3/4] tpm, tpm2-cmd: Use stack for trivial cases

From: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>

Use stack allocation for trivial "low-hanging fruit" sites, which are often
also critical code paths associated with probing and power management.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
---
 drivers/char/tpm/tpm2-cmd.c | 57 ++++++++++++++-----------------------
 1 file changed, 22 insertions(+), 35 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 245c7c952e82..3c55f60ae4c2 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -382,14 +382,13 @@ EXPORT_SYMBOL_GPL(tpm2_get_tpm_pt);
  */
 void tpm2_shutdown(struct tpm_chip *chip, u16 shutdown_type)
 {
-	struct tpm_buf *buf __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!buf)
-		return;
+	u8 buf_data[TPM_BUF_MIN_SIZE];
+	struct tpm_buf *buf = (struct tpm_buf *)buf_data;
 
-	tpm_buf_init(buf, TPM_BUF_MAX_SIZE);
+	tpm_buf_init(buf, TPM_BUF_MIN_SIZE);
 	tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_SHUTDOWN);
 	tpm_buf_append_u16(buf, shutdown_type);
-	tpm_transmit_cmd(chip, buf, 0, "stopping the TPM");
+	tpm_transmit_cmd(chip, buf, 0, "TPM2_Shutdown");
 }
 
 /**
@@ -407,58 +406,49 @@ void tpm2_shutdown(struct tpm_chip *chip, u16 shutdown_type)
  */
 static int tpm2_do_selftest(struct tpm_chip *chip)
 {
+	u8 buf_data[TPM_BUF_MIN_SIZE];
+	struct tpm_buf *buf = (struct tpm_buf *)buf_data;
 	int full;
 	int rc;
 
-	struct tpm_buf *buf __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	tpm_buf_init(buf, TPM_BUF_MAX_SIZE);
-	tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_SELF_TEST);
+	tpm_buf_init(buf, TPM_BUF_MIN_SIZE);
 	for (full = 0; full < 2; full++) {
 		tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_SELF_TEST);
 		tpm_buf_append_u8(buf, full);
-		rc = tpm_transmit_cmd(chip, buf, 0,
-				      "attempting the self test");
-
+		rc = tpm_transmit_cmd(chip, buf, 0, "TPM2_SelfTest");
 		if (rc == TPM2_RC_TESTING)
 			rc = TPM2_RC_SUCCESS;
 		if (rc == TPM2_RC_INITIALIZE || rc == TPM2_RC_SUCCESS)
 			return rc;
 	}
-
 	return rc;
 }
 
 /**
- * tpm2_probe() - probe for the TPM 2.0 protocol
+ * tpm2_probe() - Probe for the TPM 2.0 protocol
  * @chip:	a &tpm_chip instance
  *
- * Send an idempotent TPM 2.0 command and see whether there is TPM2 chip in the
- * other end based on the response tag. The flag TPM_CHIP_FLAG_TPM2 is set by
- * this function if this is the case.
+ * Sends an idempotent TPM 2.0 command, and based on the response tag deduces
+ * whether a functional TPM2 chip is on the other side. When the result is
+ * positive, TPM_CHIP_FLAG_TPM2 is append to the chip's flags.
  *
  * Return:
- *   0 on success,
- *   -errno otherwise
+ * * 0 on success,
+ * * -errno otherwise
  */
 int tpm2_probe(struct tpm_chip *chip)
 {
+	u8 buf_data[TPM_BUF_MIN_SIZE];
+	struct tpm_buf *buf = (struct tpm_buf *)buf_data;
 	struct tpm_header *out;
 	int rc;
 
-	struct tpm_buf *buf __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	tpm_buf_init(buf, TPM_BUF_MAX_SIZE);
+	tpm_buf_init(buf, TPM_BUF_MIN_SIZE);
 	tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_GET_CAPABILITY);
 	tpm_buf_append_u32(buf, TPM2_CAP_TPM_PROPERTIES);
 	tpm_buf_append_u32(buf, TPM_PT_TOTAL_COMMANDS);
 	tpm_buf_append_u32(buf, 1);
 	rc = tpm_transmit_cmd(chip, buf, 0, NULL);
-	/* We ignore TPM return codes on purpose. */
 	if (rc >=  0) {
 		out = (struct tpm_header *)buf->data;
 		if (be16_to_cpu(out->tag) == TPM2_ST_NO_SESSIONS)
@@ -651,17 +641,14 @@ EXPORT_SYMBOL_GPL(tpm2_get_cc_attrs_tbl);
 
 static int tpm2_startup(struct tpm_chip *chip)
 {
-	struct tpm_buf *buf __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	dev_info(&chip->dev, "starting up the TPM manually\n");
+	u8 buf_data[TPM_BUF_MIN_SIZE];
+	struct tpm_buf *buf = (struct tpm_buf *)buf_data;
 
-	tpm_buf_init(buf, TPM_BUF_MAX_SIZE);
+	dev_info(&chip->dev, "TPM2_Startup\n");
+	tpm_buf_init(buf, TPM_BUF_MIN_SIZE);
 	tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_STARTUP);
 	tpm_buf_append_u16(buf, TPM2_SU_CLEAR);
-
-	return tpm_transmit_cmd(chip, buf, 0, "attempting to start the TPM");
+	return tpm_transmit_cmd(chip, buf, 0, "TPM2_Startup");
 }
 
 /**
-- 
2.39.5