linux-kernel - Re: [PATCH] tpm2-sessions: Remove unnecessary wrapper

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Message-ID: <aNOtTIRBrzN_AAMa@earth.li>
Date: Wed, 24 Sep 2025 09:35:24 +0100
From: Jonathan McDowell <noodles@...th.li>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-integrity@...r.kernel.org,
	Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
	Peter Huewe <peterhuewe@....de>, 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>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:KEYS/KEYRINGS" <keyrings@...r.kernel.org>,
	"open list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] tpm2-sessions: Remove unnecessary wrapper

On Mon, Sep 22, 2025 at 02:50:09PM +0300, Jarkko Sakkinen wrote:
>From: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
>
>Open code tpm_buf_append_hmac_session_opt() because it adds unnecessary
>disperancy to the call sites (and reduces the amount of code).
>
>Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>

I don't have a strong opinion on whether this is significantly better, 
but for 2 call sites it's not unreasonable, so:

Reviewed-By: Jonathan McDowell <noodles@...th.li>

>---
> drivers/char/tpm/tpm2-cmd.c               | 14 +++++++++++---
> include/linux/tpm.h                       | 23 -----------------------
> security/keys/trusted-keys/trusted_tpm2.c | 12 ++++++++++--
> 3 files changed, 21 insertions(+), 28 deletions(-)
>
>diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
>index 7d77f6fbc152..89e6169add88 100644
>--- a/drivers/char/tpm/tpm2-cmd.c
>+++ b/drivers/char/tpm/tpm2-cmd.c
>@@ -257,9 +257,17 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
>
> 	do {
> 		tpm_buf_reset(&buf, TPM2_ST_SESSIONS, TPM2_CC_GET_RANDOM);
>-		tpm_buf_append_hmac_session_opt(chip, &buf, TPM2_SA_ENCRYPT
>-						| TPM2_SA_CONTINUE_SESSION,
>-						NULL, 0);
>+		if (tpm2_chip_auth(chip)) {
>+			tpm_buf_append_hmac_session(chip, &buf,
>+						    TPM2_SA_ENCRYPT |
>+						    TPM2_SA_CONTINUE_SESSION,
>+						    NULL, 0);
>+		} else  {
>+			offset = buf.handles * 4 + TPM_HEADER_SIZE;
>+			head = (struct tpm_header *)buf.data;
>+			if (tpm_buf_length(&buf) == offset)
>+				head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
>+		}
> 		tpm_buf_append_u16(&buf, num_bytes);
> 		tpm_buf_fill_hmac_session(chip, &buf);
> 		err = tpm_transmit_cmd(chip, &buf,
>diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>index 667d290789ca..aaa407ddef21 100644
>--- a/include/linux/tpm.h
>+++ b/include/linux/tpm.h
>@@ -534,29 +534,6 @@ void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
> 				 int passphraselen);
> void tpm_buf_append_auth(struct tpm_chip *chip, struct tpm_buf *buf,
> 			 u8 attributes, u8 *passphrase, int passphraselen);
>-static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
>-						   struct tpm_buf *buf,
>-						   u8 attributes,
>-						   u8 *passphrase,
>-						   int passphraselen)
>-{
>-	struct tpm_header *head;
>-	int offset;
>-
>-	if (tpm2_chip_auth(chip)) {
>-		tpm_buf_append_hmac_session(chip, buf, attributes, passphrase, passphraselen);
>-	} else  {
>-		offset = buf->handles * 4 + TPM_HEADER_SIZE;
>-		head = (struct tpm_header *)buf->data;
>-
>-		/*
>-		 * If the only sessions are optional, the command tag must change to
>-		 * TPM2_ST_NO_SESSIONS.
>-		 */
>-		if (tpm_buf_length(buf) == offset)
>-			head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
>-	}
>-}
>
> #ifdef CONFIG_TCG_TPM2_HMAC
>
>diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
>index e165b117bbca..c414a7006d78 100644
>--- a/security/keys/trusted-keys/trusted_tpm2.c
>+++ b/security/keys/trusted-keys/trusted_tpm2.c
>@@ -482,8 +482,10 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
> 			   struct trusted_key_options *options,
> 			   u32 blob_handle)
> {
>+	struct tpm_header *head;
> 	struct tpm_buf buf;
> 	u16 data_len;
>+	int offset;
> 	u8 *data;
> 	int rc;
>
>@@ -518,8 +520,14 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
> 		tpm2_buf_append_auth(&buf, options->policyhandle,
> 				     NULL /* nonce */, 0, 0,
> 				     options->blobauth, options->blobauth_len);
>-		tpm_buf_append_hmac_session_opt(chip, &buf, TPM2_SA_ENCRYPT,
>-						NULL, 0);
>+		if (tpm2_chip_auth(chip)) {
>+			tpm_buf_append_hmac_session(chip, &buf, TPM2_SA_ENCRYPT, NULL, 0);
>+		} else  {
>+			offset = buf.handles * 4 + TPM_HEADER_SIZE;
>+			head = (struct tpm_header *)buf.data;
>+			if (tpm_buf_length(&buf) == offset)
>+				head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
>+		}
> 	}
>
> 	tpm_buf_fill_hmac_session(chip, &buf);
>-- 
>2.39.5
>
>

J.

-- 
"Where else in computing can a random government that isn't even in
your country force you to make a change to your servers on three day's
notice?" -- Russ Allbery on DST