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Message-Id: <D4ENBEH902OY.2HO91169I3HV0@kernel.org>
Date: Tue, 24 Sep 2024 19:13:22 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "James Bottomley" <James.Bottomley@...senPartnership.com>,
<linux-integrity@...r.kernel.org>
Cc: <roberto.sassu@...wei.com>, <mapengyu@...il.com>,
<stable@...r.kernel.org>, "Mimi Zohar" <zohar@...ux.ibm.com>, "David
Howells" <dhowells@...hat.com>, "Paul Moore" <paul@...l-moore.com>, "James
Morris" <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, "Peter
Huewe" <peterhuewe@....de>, "Jason Gunthorpe" <jgg@...pe.ca>,
<keyrings@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/5] tpm: Allocate chip->auth in
tpm2_start_auth_session()
On Tue Sep 24, 2024 at 4:33 PM EEST, James Bottomley wrote:
> On Sat, 2024-09-21 at 15:08 +0300, 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@...r.kernel.org # v6.10+
> > Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
> > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.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 1aef5b1f9c90..a8d3d5d52178 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)
>
> This addition of auth as an argument is a bit unnecessary. You can set
> chip->auth before calling this and it will all function. Since there's
> no error leg in tpm2_start_auth_session unless the session creation
> itself fails and the guarantee of the ops lock is single threading this
> chip->auth can be nulled again in that error leg.
>
> If you want to keep the flow proposed in the patch, the change from how
> it works now to how it works with this patch needs documenting in the
> change log
OK, I don't want to overgrow the diff so +1 for this.
>
> > {
> > 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:
> > + kfree(auth);
> > return rc;
> > }
> > EXPORT_SYMBOL(tpm2_start_auth_session);
> > @@ -1371,10 +1382,6 @@ int tpm2_sessions_init(struct tpm_chip *chip)
> > if (rc)
> > return rc;
> >
> > - chip->auth = kmalloc(sizeof(*chip->auth), GFP_KERNEL);
> > - if (!chip->auth)
> > - return -ENOMEM;
> > -
> > return rc;
> > }
> > #endif /* CONFIG_TCG_TPM2_HMAC */
>
> Other than the comment above
>
> Reviewed-by: James Bottomley <James.Bottomley@...senPartnership.com>
Just in case, I'll address the comment so please check also v6.
BR, Jarkko
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