linux-kernel - Re: [tpmdd-devel] [RFC] tpm2-space: add handling for global session exhaustion

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Date:   Thu, 09 Feb 2017 11:29:51 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Ken Goldman <kgoldman@...ibm.com>, greg@...ellic.com,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [RFC] tpm2-space: add handling for global session
 exhaustion

On Thu, 2017-02-09 at 12:04 -0700, Jason Gunthorpe wrote:
> On Thu, Feb 09, 2017 at 05:19:22PM +0200, Jarkko Sakkinen wrote:
> > The current patch set does not define policy. The simple policy
> > addition that could be added soon is the limit of connections
> > because it is easy to implement in non-intrusive way.
> 
> It is also trivial for a userspace RM to limit the number of sessions
> or connections or otherwise to manage this limitation. It is hard to
> see why we'd need kernel support for this.

Because the kernel is a primary TPM user.  We can't have the kernel
call on the in-userspace resource manager without causing a deadlock,
so we need as much of the RM as is needed to support the kernel in the
kernel itself.

James