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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Dec 19, 2025 at 09:32:02AM +0000, Jonathan McDowell wrote:
> 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".

Thanks, yeah, I can fix this up :-)

> 
> > + * 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?
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BR, Jarkko