^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. SPDX-License-Identifier: GPL-2.0+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) .. Copyright (C) 2020 Google LLC.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) LSM BPF Programs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) ================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) These BPF programs allow runtime instrumentation of the LSM hooks by privileged
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) users to implement system-wide MAC (Mandatory Access Control) and Audit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) policies using eBPF.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) Structure
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) ---------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) The example shows an eBPF program that can be attached to the ``file_mprotect``
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) LSM hook:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) .. c:function:: int file_mprotect(struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) Other LSM hooks which can be instrumented can be found in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) ``include/linux/lsm_hooks.h``.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) eBPF programs that use :doc:`/bpf/btf` do not need to include kernel headers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) for accessing information from the attached eBPF program's context. They can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) simply declare the structures in the eBPF program and only specify the fields
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) that need to be accessed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) .. code-block:: c
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) struct mm_struct {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) unsigned long start_brk, brk, start_stack;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) } __attribute__((preserve_access_index));
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) struct vm_area_struct {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) unsigned long start_brk, brk, start_stack;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) unsigned long vm_start, vm_end;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) struct mm_struct *vm_mm;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) } __attribute__((preserve_access_index));
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) .. note:: The order of the fields is irrelevant.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) This can be further simplified (if one has access to the BTF information at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) build time) by generating the ``vmlinux.h`` with:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) .. code-block:: console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) # bpftool btf dump file <path-to-btf-vmlinux> format c > vmlinux.h
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) .. note:: ``path-to-btf-vmlinux`` can be ``/sys/kernel/btf/vmlinux`` if the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) build environment matches the environment the BPF programs are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) deployed in.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) The ``vmlinux.h`` can then simply be included in the BPF programs without
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) requiring the definition of the types.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) The eBPF programs can be declared using the``BPF_PROG``
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) macros defined in `tools/lib/bpf/bpf_tracing.h`_. In this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) example:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) * ``"lsm/file_mprotect"`` indicates the LSM hook that the program must
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) be attached to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) * ``mprotect_audit`` is the name of the eBPF program
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) .. code-block:: c
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) SEC("lsm/file_mprotect")
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) int BPF_PROG(mprotect_audit, struct vm_area_struct *vma,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) unsigned long reqprot, unsigned long prot, int ret)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) /* ret is the return value from the previous BPF program
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) * or 0 if it's the first hook.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) if (ret != 0)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) return ret;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) int is_heap;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) is_heap = (vma->vm_start >= vma->vm_mm->start_brk &&
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) vma->vm_end <= vma->vm_mm->brk);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) /* Return an -EPERM or write information to the perf events buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) * for auditing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) if (is_heap)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) return -EPERM;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) The ``__attribute__((preserve_access_index))`` is a clang feature that allows
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) the BPF verifier to update the offsets for the access at runtime using the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) :doc:`/bpf/btf` information. Since the BPF verifier is aware of the types, it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) also validates all the accesses made to the various types in the eBPF program.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) Loading
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) -------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) eBPF programs can be loaded with the :manpage:`bpf(2)` syscall's
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) ``BPF_PROG_LOAD`` operation:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) .. code-block:: c
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) struct bpf_object *obj;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) obj = bpf_object__open("./my_prog.o");
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) bpf_object__load(obj);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) This can be simplified by using a skeleton header generated by ``bpftool``:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) .. code-block:: console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) # bpftool gen skeleton my_prog.o > my_prog.skel.h
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) and the program can be loaded by including ``my_prog.skel.h`` and using
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) the generated helper, ``my_prog__open_and_load``.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) Attachment to LSM Hooks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) -----------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) The LSM allows attachment of eBPF programs as LSM hooks using :manpage:`bpf(2)`
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) syscall's ``BPF_RAW_TRACEPOINT_OPEN`` operation or more simply by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) using the libbpf helper ``bpf_program__attach_lsm``.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) The program can be detached from the LSM hook by *destroying* the ``link``
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) link returned by ``bpf_program__attach_lsm`` using ``bpf_link__destroy``.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) One can also use the helpers generated in ``my_prog.skel.h`` i.e.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) ``my_prog__attach`` for attachment and ``my_prog__destroy`` for cleaning up.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) Examples
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) --------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) An example eBPF program can be found in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) `tools/testing/selftests/bpf/progs/lsm.c`_ and the corresponding
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) userspace code in `tools/testing/selftests/bpf/prog_tests/test_lsm.c`_
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) .. Links
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) .. _tools/lib/bpf/bpf_tracing.h:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/lib/bpf/bpf_tracing.h
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) .. _tools/testing/selftests/bpf/progs/lsm.c:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/lsm.c
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) .. _tools/testing/selftests/bpf/prog_tests/test_lsm.c:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/prog_tests/test_lsm.c
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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