On 2/20/24 17:23, Jarkko Sakkinen wrote:
On Tue Feb 20, 2024 at 8:54 PM UTC, Lino Sanfilippo wrote:
Hi,
On 20.02.24 19:42, Alexander Steffen wrote:
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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.
Usually, or at least use cases I'm aware of, localities are per
component. E.g. Intel TXT has one and Linux has another.
There's been some proposals in the past here for hypervisor specific
locality here at LKML they didn't lead to anything.
If you are suggesting of removing "int l" parameter altogether, I
do support that idea.
But this is rather code optimization and not really required to fix
the reported bug.
Just adding here that I wish we also had a log transcript of bug, which
is right now missing. The explanation believable enough to move forward
but I still wish to see a log transcript.
That will be forth coming.
v/r,
dps
