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
