From: "Daniel P. Smith" <dpsmith@apertussolutions.com>
To: Jarkko Sakkinen <jarkko@kernel.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Ross Philipson <ross.philipson@oracle.com>,
Peter Huewe <peterhuewe@gmx.de>
Subject: Re: [PATCH 3/3] tpm: make locality request return value consistent
Date: Mon, 19 Feb 2024 15:29:30 -0500 [thread overview]
Message-ID: <80d95a08-a1c1-44a7-959c-8bff14254608@apertussolutions.com> (raw)
In-Reply-To: <CYU3XUGOX6QT.1GL070ONNPBWQ@suppilovahvero>
On 2/1/24 17:49, Jarkko Sakkinen wrote:
> On Wed Jan 31, 2024 at 7:08 PM EET, Daniel P. Smith wrote:
>> The function tpm_tis_request_locality() is expected to return the locality
>> value that was requested, or a negative error code upon failure. If it is called
>> while locality_count of struct tis_data is non-zero, no actual locality request
>> will be sent. Because the ret variable is initially set to 0, the
>> locality_count will still get increased, and the function will return 0. For a
>> caller, this would indicate that locality 0 was successfully requested and not
>> the state changes just mentioned.
>>
>> Additionally, the function __tpm_tis_request_locality() provides inconsistent
>> error codes. It will provide either a failed IO write or a -1 should it have
>> timed out waiting for locality request to succeed.
>>
>> This commit changes __tpm_tis_request_locality() to return valid negative error
>> codes to reflect the reason it fails. It then adjusts the return value check in
>> tpm_tis_request_locality() to check for a non-negative return value before
>> incrementing locality_cout. In addition, the initial value of the ret value is
>> set to a negative error to ensure the check does not pass if
>> __tpm_tis_request_locality() is not called.
>
> This is way way too abtract explanation and since I don't honestly
> understand what I'm reading, the code changes look bunch of arbitrary
> changes with no sound logic as a whole.
In more simpler terms, the interface is inconsistent with its return
values. To be specific, here are the sources for the possible values
tpm_tis_request_locality() will return:
1. 0 - 4: _tpm_tis_request_locality() was able to set the locality
2. 0: a locality already open, no locality request made
3. -1: if timeout happens in __tpm_tis_request_locality()
4. -EINVAL: unlikely, return by IO write for incorrect sized write
As can easily be seen, tpm_tis_request_locality() will return 0 for both
a successful(1) and non-successful request(2). And to be explicit for
(2), if tpm_tis_request_locality is called for a non-zero locality and
the locality counter is not zero, it will return 0. Thus, making the
value 0 reflect as success when locality 0 is successfully requested and
as failure when a locality is requested with a locality already open.
As for failures, correct me if I am wrong, but if a function is
returning negative error codes, it should not be using a hard coded -1
as a generic error code. As I note, it is unlikely for the -EINVAL to be
delivered, but the code path is still available should something in the
future change the backing call logic.
After this change, the possible return values for
tpm_tis_request_locality() become:
1. 0 - 4: the locality that was successfully requested
2. -EBUSY: tpm busy, unable to request locality
3. -EINVAL: invalid parameter
With this more consistent interface, I updated the return value checks
at the call sites to check for negative error as the means to catch
failures.
v/r,
dps
next prev parent reply other threads:[~2024-02-19 20:29 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
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 [this message]
2024-02-19 20:45 ` Jarkko Sakkinen
2024-02-20 18:57 ` Alexander Steffen
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