From: Alexander Steffen <Alexander.Steffen@infineon.com>
To: Lino Sanfilippo <l.sanfilippo@kunbus.com>,
Jarkko Sakkinen <jarkko@kernel.org>,
"Daniel P. Smith" <dpsmith@apertussolutions.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>, Sasha Levin <sashal@kernel.org>,
<linux-integrity@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: Ross Philipson <ross.philipson@oracle.com>,
Kanth Ghatraju <kanth.ghatraju@oracle.com>,
Peter Huewe <peterhuewe@gmx.de>
Subject: Re: [PATCH 1/3] tpm: protect against locality counter underflow
Date: Tue, 20 Feb 2024 19:42:24 +0100 [thread overview]
Message-ID: <ae3fecc4-7b76-4607-8749-045e17941923@infineon.com> (raw)
In-Reply-To: <2ba9a96e-f93b-48e2-9ca0-48318af7f9b1@kunbus.com>
On 02.02.2024 04:08, Lino Sanfilippo wrote:
> On 01.02.24 23:21, Jarkko Sakkinen wrote:
>
>>
>> On Wed Jan 31, 2024 at 7:08 PM EET, Daniel P. Smith wrote:
>>> Commit 933bfc5ad213 introduced the use of a locality counter to control when a
>>> locality request is allowed to be sent to the TPM. In the commit, the counter
>>> is indiscriminately decremented. Thus creating a situation for an integer
>>> underflow of the counter.
>>
>> What is the sequence of events that leads to this triggering the
>> underflow? This information should be represent in the commit message.
>>
>
> AFAIU this is:
>
> 1. We start with a locality_counter of 0 and then we call tpm_tis_request_locality()
> for the first time, but since a locality is (unexpectedly) already active
> check_locality() and consequently __tpm_tis_request_locality() return "true".
check_locality() returns true, but __tpm_tis_request_locality() returns
the requested locality. Currently, this is always 0, so the check for
!ret will always correctly indicate success and increment the
locality_count.
But since theoretically a locality != 0 could be requested, the correct
fix would be to check for something like ret >= 0 or ret == l instead of
!ret. Then the counter will also be incremented correctly for localities
!= 0, and no underflow will happen later on. Therefore, explicitly
checking for an underflow is unnecessary and hides the real problem.
> This prevents the locality_counter from being increased to 1, see
>
> ret = __tpm_tis_request_locality(chip, l);
> if (!ret) /* Counter not increased since ret == 1 */
> priv->locality_count++;
>
> in tpm_tis_request_locality().
>
> If now the locality is released the counter is decreased to below zero (resulting
> in an underflow since "locality_counter" is an unsigned int.
next prev parent reply other threads:[~2024-02-20 18:43 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20240131170824.6183-1-dpsmith@apertussolutions.com>
2024-01-31 17:08 ` [PATCH 1/3] tpm: protect against locality counter underflow Daniel P. Smith
2024-02-01 22:21 ` Jarkko Sakkinen
2024-02-02 3:08 ` Lino Sanfilippo
2024-02-12 20:05 ` Jarkko Sakkinen
2024-02-19 17:54 ` Daniel P. Smith
2024-02-20 18:42 ` Alexander Steffen [this message]
2024-02-20 19:04 ` Jarkko Sakkinen
2024-02-20 20:54 ` Lino Sanfilippo
2024-02-20 22:23 ` Jarkko Sakkinen
2024-02-20 23:19 ` Lino Sanfilippo
2024-02-21 0:40 ` Jarkko Sakkinen
2024-02-23 1:58 ` Daniel P. Smith
2024-02-23 12:58 ` Jarkko Sakkinen
2024-02-25 11:23 ` Daniel P. Smith
2024-02-26 9:39 ` Jarkko Sakkinen
2024-02-20 22:26 ` Jarkko Sakkinen
2024-02-20 22:31 ` Jarkko Sakkinen
2024-02-20 23:26 ` Lino Sanfilippo
2024-02-21 0:42 ` Jarkko Sakkinen
2024-02-21 12:37 ` James Bottomley
2024-02-21 19:43 ` Jarkko Sakkinen
2024-02-21 19:45 ` Jarkko Sakkinen
2024-02-22 9:06 ` James Bottomley
2024-02-22 23:49 ` Jarkko Sakkinen
2024-02-23 1:57 ` Daniel P. Smith
2024-02-23 20:40 ` Jarkko Sakkinen
2024-02-23 20:42 ` Jarkko Sakkinen
2024-02-23 1:57 ` Daniel P. Smith
2024-02-23 20:50 ` Jarkko Sakkinen
2024-02-20 22:57 ` ross.philipson
2024-02-20 23:10 ` Jarkko Sakkinen
2024-02-20 23:13 ` Jarkko Sakkinen
2024-02-23 1:56 ` Daniel P. Smith
2024-02-23 20:44 ` Jarkko Sakkinen
2024-02-24 2:34 ` Lino Sanfilippo
2024-02-26 9:38 ` Jarkko Sakkinen
2024-02-23 1:55 ` Daniel P. Smith
2024-02-26 12:43 ` Alexander Steffen
2024-02-24 2:06 ` Lino Sanfilippo
2024-02-23 0:01 ` Jarkko Sakkinen
2024-01-31 17:08 ` [PATCH 2/3] tpm: ensure tpm is in known state at startup Daniel P. Smith
2024-02-01 22:33 ` Jarkko Sakkinen
2024-02-19 19:17 ` Daniel P. Smith
2024-02-19 20:17 ` Jarkko Sakkinen
2024-01-31 17:08 ` [PATCH 3/3] tpm: make locality request return value consistent Daniel P. Smith
2024-02-01 22:49 ` Jarkko Sakkinen
2024-02-19 20:29 ` Daniel P. Smith
2024-02-19 20:45 ` Jarkko Sakkinen
2024-02-20 18:57 ` Alexander Steffen
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