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

On Thu Oct 24, 2024 at 3:59 PM EEST, Stefan Berger wrote:

On 10/24/24 7:28 AM, Jarkko Sakkinen wrote:

...

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().

And change the other ones that use memzero_explicit()?

Yeah, might be a good idea too. Don't invent your own "safe primitives" sounds like a good idea to me at least...

...

BR, Jarkko

BR, Jarkko