Re: [PATCH v3 05/10] tpm2-sessions: Umask tpm_buf_append_hmac_session()

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Sep 30, 2025 at 12:11:47PM +0100, Jonathan McDowell wrote:
> On Mon, Sep 29, 2025 at 10:48:27PM +0300, Jarkko Sakkinen wrote:
> > From: Jarkko Sakkinen <jarkko.sakkinen@opinsys.com>
> > 
> > Open code tpm_buf_append_hmac_session_opt() in order to unmask the code
> > paths in the call sites of tpm_buf_append_hmac_session().
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@opinsys.com>
> 
> Reviewed-by: Jonathan McDowell <noodles@meta.com>

Thanks (short summary has a typo tho) 

> 
> > ---
> > v3:
> > - No changes.
> > v2:
> > - Uncorrupt the patch.
> > ---
> >  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 86b1a4d859b9..c7bfa705ea8f 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 1fa02e18e688..e72e7657faa2 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -532,29 +532,6 @@ 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 *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.
> 
> -- 
> ... I love you the way a bomb loves a crowd.

BR, Jarkko