One of the desirable features in security is the ability to restrict import of data to a given system based on data authenticity. If data import can be restricted, it would be possible to enforce a system-wide policy based on the signing keys the system owner trusts.
This feature is widely used in the kernel. For example, if the restriction is enabled, kernel modules can be plugged in only if they are signed with a key whose public part is in the primary or secondary keyring.
For eBPF, it can be useful as well. For example, it might be useful to authenticate data an eBPF program makes security decisions on.
After a discussion in the eBPF mailing list, it was decided that the stated goal should be accomplished by introducing a new helper: bpf_verify_pkcs7_signature(). It is simply a wrapper of verify_pkcs7_signature(), and does the signature verification with a key in the selected keyring (primary, secondary or platform).
Since verify_pkcs7_signature() is doing crypto operations, it must be called by a sleepable program. This restricts the set of functions that can call the associated helper (for example, lsm.s/bpf is suitable, fexit/array_map_update_elem is not).
The added test check the ability of an eBPF program to verify module-style appended signatures, as produced by the kernel tool sign-file, currently used to sign kernel modules.
The patch set is organized as follows.
Patch 1 introduces the new helper. Patch 2 adds two new options to test_progs (the eBPF selftest binary), to specify the path of sign-file and the file containing the kernel private key and certificate. Finally, patch 3 adds the test for the new helper.
Roberto Sassu (3): bpf: Add bpf_verify_pkcs7_signature() helper selftests/bpf: Add test_progs opts for sign-file and kernel priv key + cert selftests/bpf: Add test for bpf_verify_pkcs7_signature() helper
include/uapi/linux/bpf.h | 8 + kernel/bpf/bpf_lsm.c | 32 ++++ tools/include/uapi/linux/bpf.h | 8 + tools/testing/selftests/bpf/config | 2 + .../bpf/prog_tests/verify_pkcs7_sig.c | 149 ++++++++++++++++++ .../bpf/progs/test_verify_pkcs7_sig.c | 127 +++++++++++++++ tools/testing/selftests/bpf/test_progs.c | 12 ++ tools/testing/selftests/bpf/test_progs.h | 3 + 8 files changed, 341 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/verify_pkcs7_sig.c create mode 100644 tools/testing/selftests/bpf/progs/test_verify_pkcs7_sig.c