[v7,bpf-next,0/9] bpf: File verification with LSM and fsverity

Message

Song Liu Nov. 2, 2023, 4:54 p.m. UTC

Changes v6 => v7:
1. Change "__const_str" annotation to "__str". (Alexei, Andrii)
2. Add KF_TRUSTED_ARGS flag for both new kfuncs. (KP)
3. Only allow bpf_get_file_xattr() to read xattr with "user." prefix.
4. Add Acked-by from Eric Biggers.

Changes v5 => v6:
1. Let fsverity_init_bpf() return void. (Eric Biggers)
2. Sort things in alphabetic orders. (Eric Biggers)

Changes v4 => v5:
1. Revise commit logs. (Alexei)

Changes v3 => v4:
1. Fix error reported by CI.
2. Update comments of bpf_dynptr_slice* that they may return error pointer.

Changes v2 => v3:
1. Rebase and resolve conflicts.

Changes v1 => v2:
1. Let bpf_get_file_xattr() use const string for arg "name". (Alexei)
2. Add recursion prevention with allowlist. (Alexei)
3. Let bpf_get_file_xattr() use __vfs_getxattr() to avoid recursion,
   as vfs_getxattr() calls into other LSM hooks.
4. Do not use dynptr->data directly, use helper insteadd. (Andrii)
5. Fixes with bpf_get_fsverity_digest. (Eric Biggers)
6. Add documentation. (Eric Biggers)
7. Fix some compile warnings. (kernel test robot)

This set enables file verification with BPF LSM and fsverity.

In this solution, fsverity is used to provide reliable and efficient hash
of files; and BPF LSM is used to implement signature verification (against
asymmetric keys), and to enforce access control.

This solution can be used to implement access control in complicated cases.
For example: only signed python binary and signed python script and access
special files/devices/ports.

Thanks,
Song

Song Liu (9):
  bpf: Expose bpf_dynptr_slice* kfuncs for in kernel use
  bpf: Factor out helper check_reg_const_str()
  bpf: Introduce KF_ARG_PTR_TO_CONST_STR
  bpf: Add kfunc bpf_get_file_xattr
  bpf, fsverity: Add kfunc bpf_get_fsverity_digest
  Documentation/bpf: Add documentation for filesystem kfuncs
  selftests/bpf: Sort config in alphabetic order
  selftests/bpf: Add tests for filesystem kfuncs
  selftests/bpf: Add test that uses fsverity and xattr to sign a file

 Documentation/bpf/fs_kfuncs.rst               |  21 +++
 Documentation/bpf/index.rst                   |   1 +
 Documentation/bpf/kfuncs.rst                  |  24 +++
 fs/verity/fsverity_private.h                  |  10 ++
 fs/verity/init.c                              |   1 +
 fs/verity/measure.c                           |  85 +++++++++
 include/linux/bpf.h                           |   4 +
 kernel/bpf/helpers.c                          |  16 +-
 kernel/bpf/verifier.c                         | 104 +++++++----
 kernel/trace/bpf_trace.c                      |  79 ++++++++-
 tools/testing/selftests/bpf/bpf_kfuncs.h      |  10 ++
 tools/testing/selftests/bpf/config            |   3 +-
 .../selftests/bpf/prog_tests/fs_kfuncs.c      | 132 ++++++++++++++
 .../bpf/prog_tests/verify_pkcs7_sig.c         | 163 +++++++++++++++++-
 .../selftests/bpf/progs/test_fsverity.c       |  46 +++++
 .../selftests/bpf/progs/test_get_xattr.c      |  37 ++++
 .../selftests/bpf/progs/test_sig_in_xattr.c   |  82 +++++++++
 .../bpf/progs/test_verify_pkcs7_sig.c         |   8 +-
 .../testing/selftests/bpf/verify_sig_setup.sh |  25 +++
 19 files changed, 794 insertions(+), 57 deletions(-)
 create mode 100644 Documentation/bpf/fs_kfuncs.rst
 create mode 100644 tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_fsverity.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_get_xattr.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_sig_in_xattr.c

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2.34.1