Messages in this thread | | | Date | Mon, 19 Feb 2024 15:29:30 -0500 | Subject | Re: [PATCH 3/3] tpm: make locality request return value consistent | From | "Daniel P. Smith" <> |
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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
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