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Message-ID: <Z_QV0ejAdciCO_Ma@kernel.org>
Date: Mon, 7 Apr 2025 21:13:37 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: keyrings@...r.kernel.org, stable@...r.kernel.org,
Herbert Xu <herbert@...dor.apana.org.au>,
David Howells <dhowells@...hat.com>, Lukas Wunner <lukas@...ner.de>,
Ignat Korchagin <ignat@...udflare.com>,
"David S. Miller" <davem@...emloft.net>,
Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Ard Biesheuvel <ardb@...nel.org>, linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org
Subject: Re: [PATCH v4] tpm: Mask TPM RC in tpm2_start_auth_session()
On Mon, Apr 07, 2025 at 03:51:21PM +0200, Stefano Garzarella wrote:
> On Mon, Apr 07, 2025 at 03:28:05PM +0300, Jarkko Sakkinen wrote:
> > tpm2_start_auth_session() does not mask TPM RC correctly from the callers:
> >
> > [ 28.766528] tpm tpm0: A TPM error (2307) occurred start auth session
> >
> > Process TPM RCs inside tpm2_start_auth_session(), and map them to POSIX
> > error codes.
> >
> > Cc: stable@...r.kernel.org # v6.10+
> > Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
> > Reported-by: Herbert Xu <herbert@...dor.apana.org.au>
> > Closes: https://lore.kernel.org/linux-integrity/Z_NgdRHuTKP6JK--@gondor.apana.org.au/
> > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> > ---
> > v4:
> > - tpm_to_ret()
> > v3:
> > - rc > 0
> > v2:
> > - Investigate TPM rc only after destroying tpm_buf.
> > ---
> > drivers/char/tpm/tpm2-sessions.c | 20 ++++++--------------
> > include/linux/tpm.h | 21 +++++++++++++++++++++
> > 2 files changed, 27 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
> > index 3f89635ba5e8..102e099f22c1 100644
> > --- a/drivers/char/tpm/tpm2-sessions.c
> > +++ b/drivers/char/tpm/tpm2-sessions.c
> > @@ -40,11 +40,6 @@
> > *
> > * These are the usage functions:
> > *
> > - * tpm2_start_auth_session() which allocates the opaque auth structure
> > - * and gets a session from the TPM. This must be called before
> > - * any of the following functions. The session is protected by a
> > - * session_key which is derived from a random salt value
> > - * encrypted to the NULL seed.
> > * tpm2_end_auth_session() kills the session and frees the resources.
> > * Under normal operation this function is done by
> > * tpm_buf_check_hmac_response(), so this is only to be used on
> > @@ -963,16 +958,13 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
> > }
> >
> > /**
> > - * tpm2_start_auth_session() - create a HMAC authentication session with the TPM
> > - * @chip: the TPM chip structure to create the session with
> > + * tpm2_start_auth_session() - Create an a HMAC authentication session
> > + * @chip: A TPM chip
> > *
> > - * This function loads the NULL seed from its saved context and starts
> > - * an authentication session on the null seed, fills in the
> > - * @chip->auth structure to contain all the session details necessary
> > - * for performing the HMAC, encrypt and decrypt operations and
> > - * returns. The NULL seed is flushed before this function returns.
> > + * Loads the ephemeral key (null seed), and starts an HMAC authenticated
> > + * session. The null seed is flushed before the return.
> > *
> > - * Return: zero on success or actual error encountered.
> > + * Returns zero on success, or a POSIX error code.
> > */
> > int tpm2_start_auth_session(struct tpm_chip *chip)
> > {
> > @@ -1024,7 +1016,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
> > /* hash algorithm for session */
> > tpm_buf_append_u16(&buf, TPM_ALG_SHA256);
> >
> > - rc = tpm_transmit_cmd(chip, &buf, 0, "start auth session");
> > + rc = tpm_to_ret(tpm_transmit_cmd(chip, &buf, 0, "StartAuthSession"));
> > tpm2_flush_context(chip, null_key);
> >
> > if (rc == TPM2_RC_SUCCESS)
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index 6c3125300c00..c826d5a9d894 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -257,8 +257,29 @@ enum tpm2_return_codes {
> > TPM2_RC_TESTING = 0x090A, /* RC_WARN */
> > TPM2_RC_REFERENCE_H0 = 0x0910,
> > TPM2_RC_RETRY = 0x0922,
> > + TPM2_RC_SESSION_MEMORY = 0x0903,
>
> nit: the other values are in ascending order, should we keep it or is it not
> important?
>
> (more a question for me than for the patch)
nope
>
> > };
> >
> > +/*
> > + * Convert a return value from tpm_transmit_cmd() to a POSIX return value. The
> > + * fallback return value is -EFAULT.
> > + */
> > +static inline ssize_t tpm_to_ret(ssize_t ret)
> > +{
> > + /* Already a POSIX error: */
> > + if (ret < 0)
> > + return ret;
> > +
> > + switch (ret) {
> > + case TPM2_RC_SUCCESS:
> > + return 0;
> > + case TPM2_RC_SESSION_MEMORY:
> > + return -ENOMEM;
> > + default:
> > + return -EFAULT;
> > + }
> > +}
>
> I like this and in the future we could reuse it in different places like
> tpm2_load_context() and tpm2_save_context().
>
> Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>
>
>
> BTW for my understading, looking at that code (sorry if the answer is
> obvious, but I'm learning) I'm confused about the use of tpm2_rc_value().
>
> For example in tpm2_load_context() we have:
>
> rc = tpm_transmit_cmd(chip, &tbuf, 4, NULL);
> ...
> } else if (tpm2_rc_value(rc) == TPM2_RC_HANDLE ||
> rc == TPM2_RC_REFERENCE_H0) {
>
> While in tpm2_save_context(), we have:
>
> rc = tpm_transmit_cmd(chip, &tbuf, 0, NULL);
> ...
> } else if (tpm2_rc_value(rc) == TPM2_RC_REFERENCE_H0) {
>
> So to check TPM2_RC_REFERENCE_H0 we are using tpm2_rc_value() only
> sometimes, what's the reason?
Good catch, I'll update...
TPM RC is a struct or bitfield.
>
> Thanks,
> Stefano
>
>
BR, Jarkko
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