[WIP RFC PATCH 0/6] Generic Firmware Variable Filesystem

[Daniel Axtens]

Hi all,

As PowerNV moves towards secure boot, we need a place to put secure
variables. One option that has been canvassed is to make our secure
variables look like EFI variables. This is an early sketch of another
approach where we create a generic firmware variable file system,
fwvarfs, and an OPAL Secure Variable backend for it.

In short, platforms provide a simple backend that can interface with
the hardware, and fwvarfs deals with translating that into a
filesystem that you can use. Almost all of the hard work is done by
kernfs: fwvarfs provides a pretty thin layer on top of that to make
backends a simple as possible.

Behaviour and the API is documented in Documentation/filesystems/fwvarfs.txt

To demonstrate the concept, a fully functional memory-based backend is
provided, and a read-only but userspace-compatible EFI backend.

For OPAL secure variables, I have taken Claudio's commit, tweaked it
to apply to linux-next, replaced all the EFI support with a generic
API, and then written a backend against that. There's a coming version
from Claudio that moves the opal calls towards a simple key/value
interface rather than (name, vendor) pairs - I haven't waited for
that: this is really just to demonstrate that it could be done rather
than an attempt to get mergable code.  It is also compile tested only
as I haven't yet set myself up with a test machine.

The patches are a bit rough, and there are a number of outstanding
TODOs sprinkled in everywhere. The idea is just to do a proof of
concept to inform our discussions:

 - Is this the sort of approach you'd like (generic vs specific)?
 
 - Does the backend API make sense?
 
 - Is the use of kernfs the correct decision, or is it potentially too
   limiting? (e.g. no ability to do case-insensitivity like efivarfs)

 - Is assuming flat fwvars correct or is there a firmware with a
   hierarchical structure?

Regards,
Daniel

Claudio Carvalho (1):
  powerpc/powernv: Add support for OPAL secure variables

Daniel Axtens (5):
  kernfs: add create() and unlink() hooks
  fwvarfs: a generic firmware variable filesystem
  fwvarfs: efi backend
  powerpc/powernv: Remove EFI support for OPAL secure variables
  fwvarfs: Add opal_secvar backend

 Documentation/filesystems/fwvarfs.txt        | 154 ++++++++++
 arch/powerpc/include/asm/opal-api.h          |   6 +-
 arch/powerpc/include/asm/opal-secvar.h       |  58 ++++
 arch/powerpc/include/asm/opal.h              |  10 +
 arch/powerpc/platforms/powernv/Kconfig       |   8 +
 arch/powerpc/platforms/powernv/Makefile      |   1 +
 arch/powerpc/platforms/powernv/opal-call.c   |   4 +
 arch/powerpc/platforms/powernv/opal-secvar.c | 121 ++++++++
 fs/Kconfig                                   |   1 +
 fs/Makefile                                  |   1 +
 fs/fwvarfs/Kconfig                           |  47 +++
 fs/fwvarfs/Makefile                          |  10 +
 fs/fwvarfs/efi.c                             | 177 +++++++++++
 fs/fwvarfs/fwvarfs.c                         | 294 +++++++++++++++++++
 fs/fwvarfs/fwvarfs.h                         | 124 ++++++++
 fs/fwvarfs/mem.c                             | 113 +++++++
 fs/fwvarfs/opal_secvar.c                     | 218 ++++++++++++++
 fs/kernfs/dir.c                              |  54 ++++
 include/linux/kernfs.h                       |   3 +
 include/uapi/linux/magic.h                   |   1 +
 20 files changed, 1404 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/filesystems/fwvarfs.txt
 create mode 100644 arch/powerpc/include/asm/opal-secvar.h
 create mode 100644 arch/powerpc/platforms/powernv/opal-secvar.c
 create mode 100644 fs/fwvarfs/Kconfig
 create mode 100644 fs/fwvarfs/Makefile
 create mode 100644 fs/fwvarfs/efi.c
 create mode 100644 fs/fwvarfs/fwvarfs.c
 create mode 100644 fs/fwvarfs/fwvarfs.h
 create mode 100644 fs/fwvarfs/mem.c
 create mode 100644 fs/fwvarfs/opal_secvar.c

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2.19.1