From: Roberto Sassu roberto.sassu@huawei.com
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