[PATCH 0/5] usermode_driver: Add management library and API

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

A User Mode Driver (UMD) is a specialization of a User Mode Helper (UMH),
which runs a user space process from a binary blob, and creates a
bidirectional pipe, so that the kernel can make a request to that process,
and the latter provides its response. It is currently used by bpfilter,
although it does not seem to do any useful work.

The problem is, if other users would like to implement a UMD similar to
bpfilter, they would have to duplicate the code. Instead, make an UMD
management library and API from the existing bpfilter and sockopt code,
and move it to common kernel code.

Also, define the software architecture and the main components of the
library: the UMD Manager, running in the kernel, acting as the frontend
interface to any user or kernel-originated request; the UMD Loader, also
running in the kernel, responsible to load the UMD Handler; the UMD
Handler, running in user space, responsible to handle requests from the UMD
Manager and to send to it the response.

I have two use cases, but for sake of brevity I will propose one.

I would like to add support for PGP keys and signatures in the kernel, so
that I can extend secure boot to applications, and allow/deny code
execution based on the signed file digests included in RPM headers.

While I proposed a patch set a while ago (based on a previous work of David
Howells), the main objection was that the PGP packet parser should not run
in the kernel.

That makes a perfect example for using a UMD. If the PGP parser is moved to
user space (UMD Handler), and the kernel (UMD Manager) just instantiates
the key and verifies the signature on already parsed data, this would
address the concern.

Patch 1 moves the function bpfilter_send_req() to usermode_driver.c and
makes the pipe between the kernel and the user space process suitable for
larger quantity of data (> 64K).

Patch 2 introduces the management library and API.

Patch 3 replaces the existing bpfilter and sockopt code with calls
to the management API. To use the new mechanism, sockopt itself (acts as
UMD Manager) now sends/receives messages to/from bpfilter_umh (acts as UMD
Handler), instead of bpfilter (acts as UMD Loader).

Patch 4 introduces a sample UMD, useful for other implementors, and uses it
for testing.

Patch 5 introduces the documentation of the new management library and API.

Roberto Sassu (5):
  usermode_driver: Introduce umd_send_recv() from bpfilter
  usermode_driver_mgmt: Introduce management of user mode drivers
  bpfilter: Port to user mode driver management API
  selftests/umd_mgmt: Add selftests for UMD management library
  doc: Add documentation for the User Mode Driver management library

 Documentation/driver-api/index.rst            |   1 +
 Documentation/driver-api/umd_mgmt.rst         |  99 +++++++++++++
 MAINTAINERS                                   |   9 ++
 include/linux/bpfilter.h                      |  12 +-
 include/linux/usermode_driver.h               |   2 +
 include/linux/usermode_driver_mgmt.h          |  35 +++++
 kernel/Makefile                               |   2 +-
 kernel/usermode_driver.c                      |  47 +++++-
 kernel/usermode_driver_mgmt.c                 | 137 ++++++++++++++++++
 net/bpfilter/bpfilter_kern.c                  | 120 +--------------
 net/ipv4/bpfilter/sockopt.c                   |  67 +++++----
 tools/testing/selftests/Makefile              |   1 +
 tools/testing/selftests/umd_mgmt/.gitignore   |   1 +
 tools/testing/selftests/umd_mgmt/Makefile     |  14 ++
 tools/testing/selftests/umd_mgmt/config       |   1 +
 .../selftests/umd_mgmt/sample_umd/Makefile    |  22 +++
 .../selftests/umd_mgmt/sample_umd/msgfmt.h    |  13 ++
 .../umd_mgmt/sample_umd/sample_binary_blob.S  |   7 +
 .../umd_mgmt/sample_umd/sample_handler.c      |  81 +++++++++++
 .../umd_mgmt/sample_umd/sample_loader.c       |  28 ++++
 .../umd_mgmt/sample_umd/sample_mgr.c          | 124 ++++++++++++++++
 tools/testing/selftests/umd_mgmt/umd_mgmt.sh  |  40 +++++
 22 files changed, 707 insertions(+), 156 deletions(-)
 create mode 100644 Documentation/driver-api/umd_mgmt.rst
 create mode 100644 include/linux/usermode_driver_mgmt.h
 create mode 100644 kernel/usermode_driver_mgmt.c
 create mode 100644 tools/testing/selftests/umd_mgmt/.gitignore
 create mode 100644 tools/testing/selftests/umd_mgmt/Makefile
 create mode 100644 tools/testing/selftests/umd_mgmt/config
 create mode 100644 tools/testing/selftests/umd_mgmt/sample_umd/Makefile
 create mode 100644 tools/testing/selftests/umd_mgmt/sample_umd/msgfmt.h
 create mode 100644 tools/testing/selftests/umd_mgmt/sample_umd/sample_binary_blob.S
 create mode 100644 tools/testing/selftests/umd_mgmt/sample_umd/sample_handler.c
 create mode 100644 tools/testing/selftests/umd_mgmt/sample_umd/sample_loader.c
 create mode 100644 tools/testing/selftests/umd_mgmt/sample_umd/sample_mgr.c
 create mode 100755 tools/testing/selftests/umd_mgmt/umd_mgmt.sh

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