RE: TPM resource manager returns -1 for TPM2_RC_CONTEXT_GAP

[<Andreas.Fuchs@infineon.com>]

> From: James Bottomley <James.Bottomley@HansenPartnership.com> 
> On Thu, 2023-10-19 at 16:05 +0200, Juergen Repp wrote:
> > There is an issue related to this problem on github for tpm2-tss:
> > https://github.com/tpm2-software/tpm2-tss/issues/2691 (/dev/tpmrm0 was 
> > used) The error did occur after abbout 200 signing operations when a 
> > second session was opened by a second process at the same time.
> > Kernel log:
> > [ 401.923826] tpm tpm0: tpm2_save_context: failed with a TPM error
> > 0x0901
> > [  401.925049] tpm tpm0: A TPM error (459) occurred flushing context
>
> I'm afraid that's a known problem with the Intel TSS: it saves the context, which will cause a gapping error if you keep it saved while doing other context requiring operations.  The solutions are either to implement degapping in the kernel or persuade the Intel TSS not to save contexts unnecessarily.

This is independent of the TSS used.
When you have one long lasting session being used seldomly (i.e. in Application A) and another session or multiple sessions being used frequently (i.e. in Application B), then you will hit this problem at some point.
As such ANY resource manager (in kernel or outside) needs to implement session ungaping, otherwise it will fail such scenarios.


James; on a different note:
Any contextSaves by an application or middleware will just make this problem appear earlier but the Kernel's RM will do the contextSave of A's sessions anyways.
You can easily make the same problem appear in ANY TSS and you know this very well.
So, please stop bad mouthing "not your TSS"es.