Re: [PATCH v8 05/12] tpm2-sessions: Define TPM2_NAME_MAX_SIZE

[Jonathan McDowell <noodles@earth.li>]

On Tue, Dec 16, 2025 at 11:21:39AM +0200, Jarkko Sakkinen wrote:
>Define TPM2_NAME_MAX_SIZE, which describes the maximum size for hashes
>encoded as TPMT_HA, which the prime identifier used for persistent and
>transient keys in TPM2 protocol.
>
>Set its value to 'SHA512_DIGEST_SIZE + 2', as SHA512 has the largest
>digest size of the algorithms in TCG algorithm repository.
>
>In additionl, rename TPM2_NAME_SIZE as TPM2_NULL_NAME_SIZE in order to
>avoid any possible confusion.

One minor capitalisation nit, otherwise:

Reviewed-by: Jonathan McDowell <noodles@meta.com>

>Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
>---
>v6:
>- Rewrote the commit message.
>v2:
>- Rename TPM2_NAME_SIZE as TPM2_NULL_NAME_SIZE.
>---
> drivers/char/tpm/tpm-sysfs.c     |  2 +-
> drivers/char/tpm/tpm2-sessions.c |  2 +-
> include/linux/tpm.h              | 37 +++++++++++++++++++++-----------
> 3 files changed, 27 insertions(+), 14 deletions(-)
>
>diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
>index 94231f052ea7..4a6a27ee295d 100644
>--- a/drivers/char/tpm/tpm-sysfs.c
>+++ b/drivers/char/tpm/tpm-sysfs.c
>@@ -314,7 +314,7 @@ static ssize_t null_name_show(struct device *dev, struct device_attribute *attr,
> 			      char *buf)
> {
> 	struct tpm_chip *chip = to_tpm_chip(dev);
>-	int size = TPM2_NAME_SIZE;
>+	int size = TPM2_NULL_NAME_SIZE;
>
> 	bin2hex(buf, chip->null_key_name, size);
> 	size *= 2;
>diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
>index 4149379665c4..525b8622d1c3 100644
>--- a/drivers/char/tpm/tpm2-sessions.c
>+++ b/drivers/char/tpm/tpm2-sessions.c
>@@ -137,7 +137,7 @@ struct tpm2_auth {
> 	 * we must compute and remember
> 	 */
> 	u32 name_h[AUTH_MAX_NAMES];
>-	u8 name[AUTH_MAX_NAMES][2 + SHA512_DIGEST_SIZE];
>+	u8 name[AUTH_MAX_NAMES][TPM2_MAX_NAME_SIZE];
> };
>
> #ifdef CONFIG_TCG_TPM2_HMAC
>diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>index 202da079d500..e10f2096eae7 100644
>--- a/include/linux/tpm.h
>+++ b/include/linux/tpm.h
>@@ -27,9 +27,33 @@
>
> #define TPM_DIGEST_SIZE 20	/* Max TPM v1.2 PCR size */
>
>+/*
>+ * SHA-512 is, as of today, the largest digest in the TCG algorithm repository.
>+ */
> #define TPM2_MAX_DIGEST_SIZE	SHA512_DIGEST_SIZE
>+
>+/*
>+ * A TPM name digest i.e., TPMT_HA, is a concatenation of TPM_ALG_ID of the
>+ * name algorithm and hash of TPMT_PUBLIC.
>+ */
>+#define TPM2_MAX_NAME_SIZE	(TPM2_MAX_DIGEST_SIZE + 2)
>+
>+/*
>+ * The maximum number of PCR banks.
>+ */
> #define TPM2_MAX_PCR_BANKS	8
>
>+/*
>+ * fixed define for the size of a name.  This is actually HASHALG size

"Fixed define".

>+ * plus 2, so 32 for SHA256
>+ */
>+#define TPM2_NULL_NAME_SIZE	34
>+
>+/*
>+ * The maximum size for an object context
>+ */
>+#define TPM2_MAX_CONTEXT_SIZE	4096
>+
> struct tpm_chip;
> struct trusted_key_payload;
> struct trusted_key_options;
>@@ -139,17 +163,6 @@ struct tpm_chip_seqops {
> /* fixed define for the curve we use which is NIST_P256 */
> #define EC_PT_SZ	32
>
>-/*
>- * fixed define for the size of a name.  This is actually HASHALG size
>- * plus 2, so 32 for SHA256
>- */
>-#define TPM2_NAME_SIZE	34
>-
>-/*
>- * The maximum size for an object context
>- */
>-#define TPM2_MAX_CONTEXT_SIZE 4096
>-
> struct tpm_chip {
> 	struct device dev;
> 	struct device devs;
>@@ -211,7 +224,7 @@ struct tpm_chip {
> 	/* saved context for NULL seed */
> 	u8 null_key_context[TPM2_MAX_CONTEXT_SIZE];
> 	 /* name of NULL seed */
>-	u8 null_key_name[TPM2_NAME_SIZE];
>+	u8 null_key_name[TPM2_NULL_NAME_SIZE];
> 	u8 null_ec_key_x[EC_PT_SZ];
> 	u8 null_ec_key_y[EC_PT_SZ];
> 	struct tpm2_auth *auth;
>-- 
>2.39.5
>
>

J.

-- 
Why do I get the feeling I'm going to regret this?
This .sig brought to you by the letter S and the number 50
Product of the Republic of HuggieTag