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[77.56.209.237]) by smtp.gmail.com with ESMTPSA id 127sm5388422wmd.38.2020.03.26.13.56.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2020 13:56:06 -0700 (PDT) From: KP Singh X-Google-Original-From: KP Singh Date: Thu, 26 Mar 2020 21:56:04 +0100 To: Andrii Nakryiko Cc: open list , bpf , linux-security-module@vger.kernel.org, Brendan Jackman , Florent Revest , Thomas Garnier , Alexei Starovoitov , Daniel Borkmann , James Morris , Kees Cook , Paul Turner , Jann Horn , Florent Revest , Brendan Jackman , Greg Kroah-Hartman Subject: Re: [PATCH bpf-next v7 8/8] bpf: lsm: Add Documentation Message-ID: <20200326205604.GC15273@chromium.org> References: <20200326142823.26277-1-kpsingh@chromium.org> <20200326142823.26277-9-kpsingh@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: Thanks for the reviews! On 26-Mär 12:31, Andrii Nakryiko wrote: > On Thu, Mar 26, 2020 at 7:29 AM KP Singh wrote: > > > > From: KP Singh > > > > Document how eBPF programs (BPF_PROG_TYPE_LSM) can be loaded and > > attached (BPF_LSM_MAC) to the LSM hooks. > > > > Signed-off-by: KP Singh > > Reviewed-by: Brendan Jackman > > Reviewed-by: Florent Revest > > Reviewed-by: Thomas Garnier > > --- > > This needs another pass and re-reading, has a bunch of outdated info :) Indeed :) > > > Documentation/bpf/bpf_lsm.rst | 150 ++++++++++++++++++++++++++++++++++ > > Documentation/bpf/index.rst | 1 + > > 2 files changed, 151 insertions(+) > > create mode 100644 Documentation/bpf/bpf_lsm.rst > > > > diff --git a/Documentation/bpf/bpf_lsm.rst b/Documentation/bpf/bpf_lsm.rst > > new file mode 100644 > > index 000000000000..2a2c3b4a74d4 > > --- /dev/null > > +++ b/Documentation/bpf/bpf_lsm.rst > > @@ -0,0 +1,150 @@ > > +.. 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. Since these program end up modifying the MAC policies of > > +the system, they require both ``CAP_MAC_ADMIN`` and also require > > +``CAP_SYS_ADMIN`` for the loading of BPF programs. > > + > > +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:: Only the size and the names of the fields must match the type in the > > + kernel and the order of the fields is irrelevant. > > type should match/be compatible as well? I changed it to simply be: .. 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 dump file format c > vmlinux.h > > + > > bpftool btf *dump* file Done. > > > +.. 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 > > + */ > > return missing? Fixed. > > > + } > > + > > +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 or more simply by using the the libbpf helper > > +``bpf_prog_load_xattr``: > > + > > + > > +.. code-block:: c > > + > > + struct bpf_prog_load_attr attr = { > > + .file = "./prog.o", > > + }; > > + struct bpf_object *prog_obj; > > + struct bpf_program *prog; > > + int prog_fd; > > + > > + bpf_prog_load_xattr(&attr, &prog_obj, &prog_fd); > > Can you please update this to not use deprecated/legacy APIs. Please > suggest bpf_object__open/bpf_object__load and/or BPF skeleton as an > example. Simplified and modernized this section as: 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. If this looks okay, I will send a v8 with this updated and other fixes. - KP > > > + > > +Attachment to LSM Hooks > > +----------------------- > > + > > +The LSM allows attachment of eBPF programs as LSM hooks using :manpage:`bpf(2)` > > +syscall's ``BPF_PROG_ATTACH`` operation or more simply by > > BPF_PROG_ATTACH is incorrect, it's RAW_TRACEPOINT_OPEN, isn't it? Correct, updated. Thanks! > > > +using the libbpf helper ``bpf_program__attach_lsm``. In the code shown below > > +``prog`` is the eBPF program loaded using ``BPF_PROG_LOAD``: > > + > > +.. code-block:: c > > + > > + struct bpf_link *link; > > + > > + link = bpf_program__attach_lsm(prog); > > + > > +The program can be detached from the LSM hook by *destroying* the ``link`` > > +link returned by ``bpf_program__attach_lsm``: > > + > > +.. code-block:: c > > + > > + link->destroy(); > > that's not how it works in C ;) Oops, I incorrectly picked it up from link->destroy(link); and wrote something stupid. > > bpf_link__destroy(link); Updated in the snippet posted above. - KP > > > + > > +Examples > > +-------- > > + > > +An example eBPF programs 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/progs/lsm_void_hook.c: > > + https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/lsm_void_hook.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 > > diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst > > index 7be43c5f2dcf..f99677f3572f 100644 > > --- a/Documentation/bpf/index.rst > > +++ b/Documentation/bpf/index.rst > > @@ -45,6 +45,7 @@ Program types > > prog_cgroup_sockopt > > prog_cgroup_sysctl > > prog_flow_dissector > > + bpf_lsm > > > > > > Testing and debugging BPF > > -- > > 2.20.1 > >