Re: [tpmdd-devel] [PATCH RFC 0/4] RFC: in-kernel resource manager

[Jason Gunthorpe]

On Mon, Jan 02, 2017 at 09:26:58PM -0800, James Bottomley wrote:

> OK, so I put a patch together that does this (see below). It all works
> nicely (with a udev script that sets the resource manager device to
> 0666):
> 
> jejb@jarvis:~> ls -l /dev/tpm*
> crw------- 1 root root  10,   224 Jan  2 20:54 /dev/tpm0
> crw-rw-rw- 1 root root 246, 65536 Jan  2 20:54 /dev/tpm0rm
> 
> I've modified the tss to connect to /dev/tpm0rm by default and it all
> seems to work.
> 
> The patch applies on top of your tabrm branch, by the way.

If we are making a new /dev/ node we should think more carefully about
the design.

- Do we need a cdev node for every chip? What about just '/dev/tpm' and
  we encode the chip number in the message. Since the exclusive
  locking is gone this is very doable.
- Should we get rid of the read/write protocol and use ioctl instead?
  As I understand it ioctl is more usable with seccomp and related
  schemes? I could see passing a TPM FD into a sandbox and wanting the
  sandbox only able to do do decrypt/encrypt operations, for instance.
- Something to identify tpm chips and help match key data with the
  proper chip.

Jason