On 2/20/24 15:54, Lino Sanfilippo wrote:
Hi,
On 20.02.24 19:42, Alexander Steffen wrote:
ATTENTION: This e-mail is from an external sender. Please check attachments and links before opening e.g. with mouseover.
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.
Will the TPM TIS CORE ever (have to) request another locality than 0? Maybe the best would
be to hardcode TPM_ACCESS(0) and get rid of all the locality parameters that are
passed from one function to another.
But this is rather code optimization and not really required to fix the reported bug.
Actually, doing so will break the TPM API. The function
tpm_tis_request_locality() is registered as the locality handler,
int (*request_locality)(struct tpm_chip *chip, int loc), in the tis
instance of struct tpm_class_ops{}. This is the API used by the Secure
Launch series to open Locality2 for the measurements it must record.
v/r,
dps
