BPF Archive on lore.kernel.org
 help / color / Atom feed
From: KP Singh <kpsingh@chromium.org>
To: linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	linux-security-module@vger.kernel.org
Cc: Brendan Jackman <jackmanb@google.com>,
	Florent Revest <revest@google.com>,
	Thomas Garnier <thgarnie@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	James Morris <jmorris@namei.org>,
	Kees Cook <keescook@chromium.org>,
	Thomas Garnier <thgarnie@chromium.org>,
	Michael Halcrow <mhalcrow@google.com>,
	Paul Turner <pjt@google.com>,
	Brendan Gregg <brendan.d.gregg@gmail.com>,
	Jann Horn <jannh@google.com>, Matthew Garrett <mjg59@google.com>,
	Christian Brauner <christian@brauner.io>,
	Florent Revest <revest@chromium.org>,
	Brendan Jackman <jackmanb@chromium.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, "Serge E. Hallyn" <serge@hallyn.com>,
	"David S. Miller" <davem@davemloft.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Stanislav Fomichev <sdf@google.com>,
	Quentin Monnet <quentin.monnet@netronome.com>,
	Andrey Ignatov <rdna@fb.com>, Joe Stringer <joe@wand.net.nz>
Subject: [PATCH bpf-next v4 8/8] bpf: lsm: Add Documentation
Date: Thu, 20 Feb 2020 18:52:50 +0100
Message-ID: <20200220175250.10795-9-kpsingh@chromium.org> (raw)
In-Reply-To: <20200220175250.10795-1-kpsingh@chromium.org>

From: KP Singh <kpsingh@google.com>

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 <kpsingh@google.com>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Florent Revest <revest@google.com>
Reviewed-by: Thomas Garnier <thgarnie@google.com>
---
 Documentation/bpf/bpf_lsm.rst | 147 ++++++++++++++++++++++++++++++++++
 Documentation/bpf/index.rst   |   1 +
 2 files changed, 148 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..9d7ec8cb431d
--- /dev/null
+++ b/Documentation/bpf/bpf_lsm.rst
@@ -0,0 +1,147 @@
+.. SPDX-License-Identifier: GPL-2.0+
+.. Copyright 2019 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);
+
+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.
+
+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 <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/testing/selftests/bpf/bpf_trace_helpers.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
+		 */
+	}
+
+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
+-------
+
+eBPP 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);
+
+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
+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();
+
+Examples
+--------
+
+Example eBPF programs can be found in
+`tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c`_ and `tools/testing/selftests/bpf/progs/lsm_mprotect_mac.c`_ and the corresponding
+userspace code in `tools/testing/selftests/bpf/prog_tests/lsm_mprotect.c`_
+
+.. Links
+.. _tools/testing/selftests/bpf/bpf_trace_helpers.h:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/selftests/bpf/bpf_trace_helpers.h
+.. _tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c
+.. _tools/testing/selftests/bpf/progs/lsm_mprotect_mac.c:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/lsm_mprotect_mac.c
+.. _tools/testing/selftests/bpf/prog_tests/lsm_mprotect.c:
+   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/prog_tests/lsm_mprotect.c
diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst
index 4f5410b61441..2c3d3c0cb7bb 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 BPF
-- 
2.20.1


  parent reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 17:52 [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI) KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 1/8] bpf: Introduce BPF_PROG_TYPE_LSM KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 2/8] security: Refactor declaration of LSM hooks KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs KP Singh
2020-02-21  2:25   ` Alexei Starovoitov
2020-02-21 11:47     ` KP Singh
     [not found]   ` <0ef26943-9619-3736-4452-fec536a8d169@schaufler-ca.com>
2020-02-21 11:44     ` KP Singh
2020-02-21 18:23       ` Casey Schaufler
     [not found]     ` <202002211946.A23A987@keescook>
2020-02-23 22:08       ` Alexei Starovoitov
2020-02-24 16:32         ` Casey Schaufler
2020-02-24 17:13           ` KP Singh
2020-02-24 18:45             ` Casey Schaufler
2020-02-24 21:41               ` Kees Cook
2020-02-24 22:29                 ` Casey Schaufler
2020-02-25  5:41                 ` Alexei Starovoitov
2020-02-25 15:31                   ` Kees Cook
2020-02-25 19:31                   ` KP Singh
2020-02-26  0:30                   ` Casey Schaufler
2020-02-26  5:15                     ` KP Singh
2020-02-26 15:35                       ` Casey Schaufler
2020-02-25 19:29                 ` KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 4/8] bpf: lsm: Add support for enabling/disabling BPF hooks KP Singh
2020-02-21 18:57   ` Casey Schaufler
2020-02-21 19:11     ` James Morris
2020-02-22  4:26   ` Kees Cook
2020-02-20 17:52 ` [PATCH bpf-next v4 5/8] bpf: lsm: Implement attach, detach and execution KP Singh
2020-02-21  2:17   ` Alexei Starovoitov
2020-02-21 12:02     ` KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 6/8] tools/libbpf: Add support for BPF_PROG_TYPE_LSM KP Singh
2020-02-25  6:45   ` Andrii Nakryiko
2020-02-20 17:52 ` [PATCH bpf-next v4 7/8] bpf: lsm: Add selftests " KP Singh
2020-02-20 17:52 ` KP Singh [this message]
2020-02-21 19:19 ` [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI) Casey Schaufler
2020-02-21 19:41   ` KP Singh
2020-02-21 22:31     ` Casey Schaufler
2020-02-21 23:09       ` KP Singh
2020-02-21 23:49         ` Casey Schaufler
2020-02-22  0:22       ` Kees Cook
2020-02-22  1:04         ` Casey Schaufler
2020-02-22  3:36           ` Kees Cook
2020-02-27 18:40 ` Dr. Greg

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200220175250.10795-9-kpsingh@chromium.org \
    --to=kpsingh@chromium.org \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=brendan.d.gregg@gmail.com \
    --cc=christian@brauner.io \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=gregkh@linuxfoundation.org \
    --cc=jackmanb@chromium.org \
    --cc=jackmanb@google.com \
    --cc=jannh@google.com \
    --cc=jmorris@namei.org \
    --cc=joe@wand.net.nz \
    --cc=kafai@fb.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=mhalcrow@google.com \
    --cc=mjg59@google.com \
    --cc=nicolas.ferre@microchip.com \
    --cc=pjt@google.com \
    --cc=quentin.monnet@netronome.com \
    --cc=rdna@fb.com \
    --cc=revest@chromium.org \
    --cc=revest@google.com \
    --cc=sdf@google.com \
    --cc=serge@hallyn.com \
    --cc=songliubraving@fb.com \
    --cc=thgarnie@chromium.org \
    --cc=thgarnie@google.com \
    --cc=yhs@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git