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  1. Dec 03, 2023
  3. Dec 02, 2023
    • Alexei Starovoitov's avatar
      Merge branch 'bpf-file-verification-with-lsm-and-fsverity' · 6685aadc
      Alexei Starovoitov authored 
      Song Liu says:

====================
bpf: File verification with LSM and fsverity

Changes v14 => v15:
1. Fix selftest build without CONFIG_FS_VERITY. (Alexei)
2. Add Acked-by from KP.

Changes v13 => v14:
1. Add "static" for bpf_fs_kfunc_set.
2. Add Acked-by from Christian Brauner.

Changes v12 => v13:
1. Only keep 4/9 through 9/9 of v12, as the first 3 patches already
   applied;
2. Use new macro __bpf_kfunc_[start|end]_defs().

Changes v11 => v12:
1. Fix typo (data_ptr => sig_ptr) in bpf_get_file_xattr().

Changes v10 => v11:
1. Let __bpf_dynptr_data() return const void *. (Andrii)
2. Optimize code to reuse output from __bpf_dynptr_size(). (Andrii)
3. Add __diag_ignore_all("-Wmissing-declarations") for kfunc definition.
4. Fix an off indentation. (Andrii)

Changes v9 => v10:
1. Remove WARN_ON_ONCE() from check_reg_const_str. (Alexei)

Changes v8 => v9:
1. Fix test_progs kfunc_dynptr_param/dynptr_data_null.

Changes v7 => v8:
1. Do not use bpf_dynptr_slice* in the kernel. Add __bpf_dynptr_data* and
   use them in ther kernel. (Andrii)

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
====================

Link: https://lore.kernel.org/r/20231129234417.856536-1-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      6685aadc
    • Song Liu's avatar
      selftests/bpf: Add test that uses fsverity and xattr to sign a file · 1030e915
      Song Liu authored 
      

This selftests shows a proof of concept method to use BPF LSM to enforce
file signature. This test is added to verify_pkcs7_sig, so that some
existing logic can be reused.

This file signature method uses fsverity, which provides reliable and
efficient hash (known as digest) of the file. The file digest is signed
with asymmetic key, and the signature is stored in xattr. At the run time,
BPF LSM reads file digest and the signature, and then checks them against
the public key.

Note that this solution does NOT require FS_VERITY_BUILTIN_SIGNATURES.
fsverity is only used to provide file digest. The signature verification
and access control is all implemented in BPF LSM.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-7-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      1030e915
    • Song Liu's avatar
      selftests/bpf: Add tests for filesystem kfuncs · 341f06fd
      Song Liu authored 
      

Add selftests for two new filesystem kfuncs:
  1. bpf_get_file_xattr
  2. bpf_get_fsverity_digest

These tests simply make sure the two kfuncs work. Another selftest will be
added to demonstrate how to use these kfuncs to verify file signature.

CONFIG_FS_VERITY is added to selftests config. However, this is not
sufficient to guarantee bpf_get_fsverity_digest works. This is because
fsverity need to be enabled at file system level (for example, with tune2fs
on ext4). If local file system doesn't have this feature enabled, just skip
the test.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-6-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      341f06fd
    • Song Liu's avatar
      selftests/bpf: Sort config in alphabetic order · 6b0ae456
      Song Liu authored 
      

Move CONFIG_VSOCKETS up, so the CONFIGs are in alphabetic order.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-5-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      6b0ae456
    • Song Liu's avatar
      Documentation/bpf: Add documentation for filesystem kfuncs · 0de267d9
      Song Liu authored 
      

Add a brief introduction for file system kfuncs:

  bpf_get_file_xattr()
  bpf_get_fsverity_digest()

The documentation highlights the strategy to avoid recursions of these
kfuncs.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-4-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      0de267d9
    • Song Liu's avatar
      bpf, fsverity: Add kfunc bpf_get_fsverity_digest · 67814c00
      Song Liu authored 
      

fsverity provides fast and reliable hash of files, namely fsverity_digest.
The digest can be used by security solutions to verify file contents.

Add new kfunc bpf_get_fsverity_digest() so that we can access fsverity from
BPF LSM programs. This kfunc is added to fs/verity/measure.c because some
data structure used in the function is private to fsverity
(fs/verity/fsverity_private.h).

To avoid recursion, bpf_get_fsverity_digest is only allowed in BPF LSM
programs.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Acked-by: default avatarEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20231129234417.856536-3-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      67814c00
    • Song Liu's avatar
      bpf: Add kfunc bpf_get_file_xattr · ac9c05e0
      Song Liu authored 
      

It is common practice for security solutions to store tags/labels in
xattrs. To implement similar functionalities in BPF LSM, add new kfunc
bpf_get_file_xattr().

The first use case of bpf_get_file_xattr() is to implement file
verifications with asymmetric keys. Specificially, security applications
could use fsverity for file hashes and use xattr to store file signatures.
(kfunc for fsverity hash will be added in a separate commit.)

Currently, only xattrs with "user." prefix can be read with kfunc
bpf_get_file_xattr(). As use cases evolve, we may add a dedicated prefix
for bpf_get_file_xattr().

To avoid recursion, bpf_get_file_xattr can be only called from LSM hooks.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Acked-by: default avatarChristian Brauner <brauner@kernel.org>
Acked-by: default avatarKP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-2-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      ac9c05e0
  5. Dec 01, 2023
  7. Nov 30, 2023