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diff --git a/Documentation/bpf/bpf_lsm.rst b/Documentation/bpf/bpf_lsm.rst deleted file mode 100644 index 1c0a75a51d79..000000000000 --- a/Documentation/bpf/bpf_lsm.rst +++ /dev/null @@ -1,142 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0+ -.. Copyright (C) 2020 Google LLC. - -================ -LSM BPF Programs -================ - -These BPF programs allow runtime instrumentation of the LSM hooks by privileged -users to implement system-wide MAC (Mandatory Access Control) and Audit -policies using eBPF. - -Structure ---------- - -The example shows an eBPF program that can be attached to the ``file_mprotect`` -LSM hook: - -.. c:function:: int file_mprotect(struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot); - -Other LSM hooks which can be instrumented can be found in -``include/linux/lsm_hooks.h``. - -eBPF programs that use :doc:`/bpf/btf` do not need to include kernel headers -for accessing information from the attached eBPF program's context. They can -simply declare the structures in the eBPF program and only specify the fields -that need to be accessed. - -.. code-block:: c - - struct mm_struct { - unsigned long start_brk, brk, start_stack; - } __attribute__((preserve_access_index)); - - struct vm_area_struct { - unsigned long start_brk, brk, start_stack; - unsigned long vm_start, vm_end; - struct mm_struct *vm_mm; - } __attribute__((preserve_access_index)); - - -.. note:: The order of the fields is irrelevant. - -This can be further simplified (if one has access to the BTF information at -build time) by generating the ``vmlinux.h`` with: - -.. code-block:: console - - # bpftool btf dump file <path-to-btf-vmlinux> format c > vmlinux.h - -.. note:: ``path-to-btf-vmlinux`` can be ``/sys/kernel/btf/vmlinux`` if the - build environment matches the environment the BPF programs are - deployed in. - -The ``vmlinux.h`` can then simply be included in the BPF programs without -requiring the definition of the types. - -The eBPF programs can be declared using the``BPF_PROG`` -macros defined in `tools/lib/bpf/bpf_tracing.h`_. In this -example: - - * ``"lsm/file_mprotect"`` indicates the LSM hook that the program must - be attached to - * ``mprotect_audit`` is the name of the eBPF program - -.. code-block:: c - - SEC("lsm/file_mprotect") - int BPF_PROG(mprotect_audit, struct vm_area_struct *vma, - unsigned long reqprot, unsigned long prot, int ret) - { - /* ret is the return value from the previous BPF program - * or 0 if it's the first hook. - */ - if (ret != 0) - return ret; - - int is_heap; - - is_heap = (vma->vm_start >= vma->vm_mm->start_brk && - vma->vm_end <= vma->vm_mm->brk); - - /* Return an -EPERM or write information to the perf events buffer - * for auditing - */ - if (is_heap) - return -EPERM; - } - -The ``__attribute__((preserve_access_index))`` is a clang feature that allows -the BPF verifier to update the offsets for the access at runtime using the -:doc:`/bpf/btf` information. Since the BPF verifier is aware of the types, it -also validates all the accesses made to the various types in the eBPF program. - -Loading -------- - -eBPF programs can be loaded with the :manpage:`bpf(2)` syscall's -``BPF_PROG_LOAD`` operation: - -.. code-block:: c - - struct bpf_object *obj; - - obj = bpf_object__open("./my_prog.o"); - bpf_object__load(obj); - -This can be simplified by using a skeleton header generated by ``bpftool``: - -.. code-block:: console - - # bpftool gen skeleton my_prog.o > my_prog.skel.h - -and the program can be loaded by including ``my_prog.skel.h`` and using -the generated helper, ``my_prog__open_and_load``. - -Attachment to LSM Hooks ------------------------ - -The LSM allows attachment of eBPF programs as LSM hooks using :manpage:`bpf(2)` -syscall's ``BPF_RAW_TRACEPOINT_OPEN`` operation or more simply by -using the libbpf helper ``bpf_program__attach_lsm``. - -The program can be detached from the LSM hook by *destroying* the ``link`` -link returned by ``bpf_program__attach_lsm`` using ``bpf_link__destroy``. - -One can also use the helpers generated in ``my_prog.skel.h`` i.e. -``my_prog__attach`` for attachment and ``my_prog__destroy`` for cleaning up. - -Examples --------- - -An example eBPF program can be found in -`tools/testing/selftests/bpf/progs/lsm.c`_ and the corresponding -userspace code in `tools/testing/selftests/bpf/prog_tests/test_lsm.c`_ - -.. Links -.. _tools/lib/bpf/bpf_tracing.h: - https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/lib/bpf/bpf_tracing.h -.. _tools/testing/selftests/bpf/progs/lsm.c: - https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/lsm.c -.. _tools/testing/selftests/bpf/prog_tests/test_lsm.c: - https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/prog_tests/test_lsm.c |