Re: [PATCH v7 4/5] tpm: Allocate chip->auth in tpm2_start_auth_session()

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Wed Oct 23, 2024 at 10:15 PM EEST, Stefan Berger wrote:
>
>
> On 10/21/24 1:39 AM, Jarkko Sakkinen wrote:
> > Move allocation of chip->auth to tpm2_start_auth_session() so that the
> > field can be used as flag to tell whether auth session is active or not.
> > 
> > Cc: stable@vger.kernel.org # v6.10+
> > Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > ---
> > v5:
> > - No changes.
> > v4:
> > - Change to bug.
> > v3:
> > - No changes.
> > v2:
> > - A new patch.
> > ---
> >   drivers/char/tpm/tpm2-sessions.c | 43 +++++++++++++++++++-------------
> >   1 file changed, 25 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
> > index 78c650ce4c9f..6e52785de9fd 100644
> > --- a/drivers/char/tpm/tpm2-sessions.c
> > +++ b/drivers/char/tpm/tpm2-sessions.c
> > @@ -484,7 +484,8 @@ static void tpm2_KDFe(u8 z[EC_PT_SZ], const char *str, u8 *pt_u, u8 *pt_v,
> >   	sha256_final(&sctx, out);
> >   }
> >   
> > -static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip)
> > +static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip,
> > +				struct tpm2_auth *auth)
> >   {
> >   	struct crypto_kpp *kpp;
> >   	struct kpp_request *req;
> > @@ -543,7 +544,7 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip)
> >   	sg_set_buf(&s[0], chip->null_ec_key_x, EC_PT_SZ);
> >   	sg_set_buf(&s[1], chip->null_ec_key_y, EC_PT_SZ);
> >   	kpp_request_set_input(req, s, EC_PT_SZ*2);
> > -	sg_init_one(d, chip->auth->salt, EC_PT_SZ);
> > +	sg_init_one(d, auth->salt, EC_PT_SZ);
> >   	kpp_request_set_output(req, d, EC_PT_SZ);
> >   	crypto_kpp_compute_shared_secret(req);
> >   	kpp_request_free(req);
> > @@ -554,8 +555,7 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip)
> >   	 * This works because KDFe fully consumes the secret before it
> >   	 * writes the salt
> >   	 */
> > -	tpm2_KDFe(chip->auth->salt, "SECRET", x, chip->null_ec_key_x,
> > -		  chip->auth->salt);
> > +	tpm2_KDFe(auth->salt, "SECRET", x, chip->null_ec_key_x, auth->salt);
> >   
> >    out:
> >   	crypto_free_kpp(kpp);
> > @@ -854,6 +854,8 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
> >   			/* manually close the session if it wasn't consumed */
> >   			tpm2_flush_context(chip, auth->handle);
> >   		memzero_explicit(auth, sizeof(*auth));
> > +		kfree(auth);
> > +		chip->auth = NULL;
> >   	} else {
> >   		/* reset for next use  */
> >   		auth->session = TPM_HEADER_SIZE;
> > @@ -882,6 +884,8 @@ void tpm2_end_auth_session(struct tpm_chip *chip)
> >   
> >   	tpm2_flush_context(chip, auth->handle);
> >   	memzero_explicit(auth, sizeof(*auth));
> > +	kfree(auth);
> > +	chip->auth = NULL;
> >   }
> >   EXPORT_SYMBOL(tpm2_end_auth_session);
> >   
> > @@ -970,25 +974,29 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
> >    */
> >   int tpm2_start_auth_session(struct tpm_chip *chip)
> >   {
> > +	struct tpm2_auth *auth;
> >   	struct tpm_buf buf;
> > -	struct tpm2_auth *auth = chip->auth;
> > -	int rc;
> >   	u32 null_key;
> > +	int rc;
> >   
> > -	if (!auth) {
> > -		dev_warn_once(&chip->dev, "auth session is not active\n");
> > +	if (chip->auth) {
> > +		dev_warn_once(&chip->dev, "auth session is active\n");
> >   		return 0;
> >   	}
> >   
> > +	auth = kzalloc(sizeof(*auth), GFP_KERNEL);
> > +	if (!auth)
> > +		return -ENOMEM;
> > +
> >   	rc = tpm2_load_null(chip, &null_key);
> >   	if (rc)
> > -		goto out;
> > +		goto err;
> >   
> >   	auth->session = TPM_HEADER_SIZE;
> >   
> >   	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_START_AUTH_SESS);
> >   	if (rc)
> > -		goto out;
> > +		goto err;
> >   
> >   	/* salt key handle */
> >   	tpm_buf_append_u32(&buf, null_key);
> > @@ -1000,7 +1008,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
> >   	tpm_buf_append(&buf, auth->our_nonce, sizeof(auth->our_nonce));
> >   
> >   	/* append encrypted salt and squirrel away unencrypted in auth */
> > -	tpm_buf_append_salt(&buf, chip);
> > +	tpm_buf_append_salt(&buf, chip, auth);
> >   	/* session type (HMAC, audit or policy) */
> >   	tpm_buf_append_u8(&buf, TPM2_SE_HMAC);
> >   
> > @@ -1021,10 +1029,13 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
> >   
> >   	tpm_buf_destroy(&buf);
> >   
> > -	if (rc)
> > -		goto out;
> > +	if (rc == TPM2_RC_SUCCESS) {
> > +		chip->auth = auth;
> > +		return 0;
> > +	}
> >   
> > - out:
> > +err:
>
> like in many other cases before kfree(auth):
> memzero_explicit(auth, sizeof(*auth));
>
> With this:
>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

Thanks, or should we use kfree_sensitive()?

It has some additional functionality, which is missed now:

https://elixir.bootlin.com/linux/v6.11.5/source/mm/slab_common.c#L1339

I.e. kasan_unpoison().

BR, Jarkko