From patchwork Thu Feb 20 17:52:42 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: KP Singh X-Patchwork-Id: 11394803 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7CB921395 for ; Thu, 20 Feb 2020 17:52:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4739220722 for ; Thu, 20 Feb 2020 17:52:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="Cjb//L1T" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728476AbgBTRw5 (ORCPT ); Thu, 20 Feb 2020 12:52:57 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:35915 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728119AbgBTRw5 (ORCPT ); Thu, 20 Feb 2020 12:52:57 -0500 Received: by mail-wm1-f68.google.com with SMTP id p17so3025770wma.1 for ; Thu, 20 Feb 2020 09:52:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=AX9sVXYSyo+q1qOkt8FULjn7gyqcFkCzhWtuEbC6zIQ=; b=Cjb//L1TT+kFCDPYngm1odF8rKCR1vAUKCOBnlpW5ZeuODER6B1Jc19paVX1ql6atu 51Jv7KlBe2jcxyiD8vj8xDiGhnh88TduIqF375a/Ff6OAcruboGJGRf1GugSJUmeA7Pi HO+JSPCXKlLEGg206kMgFbL8QONrPUZd2pHaE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=AX9sVXYSyo+q1qOkt8FULjn7gyqcFkCzhWtuEbC6zIQ=; b=tapUauxk/1lLkuh89XvMwcVRJrndgjKQL9VG3t14hdbyy/jtf9DdraQWLs8cMDYz09 tWU0zx13qfSH/PiSiiAls+HDWXdrTv3/wPq4mqbvVmb4X4eoN+ZvOy8oep6NhSFnXEg2 YvlogklyrkrlaUdZUrpLeTnh9NxctKQWcTYPIhgbpN4CWE12tltAr7QTVZEvNFeFMxqb lHQ4SaSWNaRUGA34HqgTXGga/34Ad833H8Xm0JyfVOQg3fD0hqlMNUEcaTmVVB+srj7E SOuqoCsf1gBag/wDPV5L/qUajl8HVk2EaFS/b1GUl12XjGu+mWkNDOJxMT5pHEo4/8vk 2Jgw== X-Gm-Message-State: APjAAAVyO2SYtrY610gksbC2qk8unnKZR7ZpJrXq9fkn+rMIYUHdpQsA HU0Q9lw1vmbXkdI1qOLRsjg/zA== X-Google-Smtp-Source: APXvYqz0omDok3dSDam2AxHkpOU3DFNsEAan/TpkPSjreO/ziNPj225T/H0UAiprN9hV8iyYa3RrWQ== X-Received: by 2002:a05:600c:1009:: with SMTP id c9mr5608558wmc.162.1582221173942; Thu, 20 Feb 2020 09:52:53 -0800 (PST) Received: from kpsingh-kernel.localdomain ([2620:0:105f:fd00:d960:542a:a1d:648a]) by smtp.gmail.com with ESMTPSA id r5sm363059wrt.43.2020.02.20.09.52.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2020 09:52:53 -0800 (PST) From: KP Singh To: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , James Morris , Kees Cook , Thomas Garnier , Michael Halcrow , Paul Turner , Brendan Gregg , Jann Horn , Matthew Garrett , Christian Brauner , Florent Revest , Brendan Jackman , Martin KaFai Lau , Song Liu , Yonghong Song , "Serge E. Hallyn" , "David S. Miller" , Greg Kroah-Hartman , Nicolas Ferre , Stanislav Fomichev , Quentin Monnet , Andrey Ignatov , Joe Stringer Subject: [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI) Date: Thu, 20 Feb 2020 18:52:42 +0100 Message-Id: <20200220175250.10795-1-kpsingh@chromium.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: From: KP Singh # v3 -> v4 https://lkml.org/lkml/2020/1/23/515 * Moved away from allocating a separate security_hook_heads and adding a new special case for arch_prepare_bpf_trampoline to using BPF fexit trampolines called from the right place in the LSM hook and toggled by static keys based on the discussion in: https://lore.kernel.org/bpf/CAG48ez25mW+_oCxgCtbiGMX07g_ph79UOJa07h=o_6B6+Q-u5g@mail.gmail.com/ * Since the code does not deal with security_hook_heads anymore, it goes from "being a BPF LSM" to "BPF program attachment to LSM hooks". * Added a new test case which ensures that the BPF programs' return value is reflected by the LSM hook. # v2 -> v3 does not change the overall design and has some minor fixes: https://lkml.org/lkml/2020/1/15/843 * LSM_ORDER_LAST is introduced to represent the behaviour of the BPF LSM * Fixed the inadvertent clobbering of the LSM Hook error codes * Added GPL license requirement to the commit log * The lsm_hook_idx is now the more conventional 0-based index * Some changes were split into a separate patch ("Load btf_vmlinux only once per object") https://lore.kernel.org/bpf/20200117212825.11755-1-kpsingh@chromium.org/ * Addressed Andrii's feedback on the BTF implementation * Documentation update for using generated vmlinux.h to simplify programs * Rebase # Changes since v1: https://lkml.org/lkml/2019/12/20/641 * Eliminate the requirement to maintain LSM hooks separately in security/bpf/hooks.h Use BPF trampolines to dynamically allocate security hooks * Drop the use of securityfs as bpftool provides the required introspection capabilities. Update the tests to use the bpf_skeleton and global variables * Use O_CLOEXEC anonymous fds to represent BPF attachment in line with the other BPF programs with the possibility to use bpf program pinning in the future to provide "permanent attachment". * Drop the logic based on prog names for handling re-attachment. * Drop bpf_lsm_event_output from this series and send it as a separate patch. # Motivation Google does analysis of rich runtime security data to detect and thwart threats in real-time. Currently, this is done in custom kernel modules but we would like to replace this with something that's upstream and useful to others. The current kernel infrastructure for providing telemetry (Audit, Perf etc.) is disjoint from access enforcement (i.e. LSMs). Augmenting the information provided by audit requires kernel changes to audit, its policy language and user-space components. Furthermore, building a MAC policy based on the newly added telemetry data requires changes to various LSMs and their respective policy languages. This patchset allows BPF programs to be attached to LSM hooks This facilitates a unified and dynamic (not requiring re-compilation of the kernel) audit and MAC policy. # Why an LSM? Linux Security Modules target security behaviours rather than the kernel's API. For example, it's easy to miss out a newly added system call for executing processes (eg. execve, execveat etc.) but the LSM framework ensures that all process executions trigger the relevant hooks irrespective of how the process was executed. Allowing users to implement LSM hooks at runtime also benefits the LSM eco-system by enabling a quick feedback loop from the security community about the kind of behaviours that the LSM Framework should be targeting. # How does it work? The patchset introduces a new eBPF (https://docs.cilium.io/en/v1.6/bpf/) program type BPF_PROG_TYPE_LSM which can only be attached to LSM hooks. Attachment requires CAP_SYS_ADMIN for loading eBPF programs and CAP_MAC_ADMIN for modifying MAC policies. The eBPF programs are attached to nop functions (bpf_lsm_) added in the LSM hooks (when CONFIG_BPF_LSM) and executed after all the statically defined hooks (i.e. the ones declared by static LSMs (eg, SELinux, AppArmor, Smack etc) allow the action. This also ensures that statically defined LSM hooks retain the behaviour of "being read-only after init", i.e. __lsm_ro_after_init and do not increase the attack surface. The branch into this nop function is guarded with a static key (jump label) and is only taken when a BPF program is attached to the LSM hook. eg. for bprm_check_security: int bpf_lsm_bprm_check_security(struct linux_binprm *bprm) { return 0; } DEFINE_STATIC_KEY_FALSE(bpf_lsm_key_bprm_check_security) // Run all static hooks for bprm_check_security and set RC if (static_key_unlikely(&bpf_lsm_key_bprm_check_security) { if (RC == 0) bpf_lsm_bprm_check_security(bprm); } Upon attachment, a BPF fexit trampoline is attached to the nop function and the static key for the LSM hook is enabled. The trampoline has code to handle the conversion from the signature of the hook to the BPF context and allows the JIT'ed BPF program to be called as a C function with the same arguments as the LSM hooks. If the attached eBPF programs returns an error (like ENOPERM), the behaviour represented by the hook is denied. Audit logs can be written using a format chosen by the eBPF program to the perf events buffer or to global eBPF variables or maps and can be further processed in user-space. # BTF Based Design The current design uses BTF (https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html, https://lwn.net/Articles/803258/) which allows verifiable read-only structure accesses by field names rather than fixed offsets. This allows accessing the hook parameters using a dynamically created context which provides a certain degree of ABI stability: // Only declare the structure and fields intended to be used // in the program struct vm_area_struct { unsigned long vm_start; } __attribute__((preserve_access_index)); // Declare the eBPF program mprotect_audit which attaches to // to the file_mprotect LSM hook and accepts three arguments. SEC("lsm/file_mprotect") int BPF_PROG(mprotect_audit, struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot) { unsigned long vm_start = vma->vm_start; return 0; } By relocating field offsets, BTF makes a large portion of kernel data structures readily accessible across kernel versions without requiring a large corpus of BPF helper functions and requiring recompilation with every kernel version. The BTF type information is also used by the BPF verifier to validate memory accesses within the BPF program and also prevents arbitrary writes to the kernel memory. The limitations of BTF compatibility are described in BPF Co-Re (http://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf, i.e. field renames, #defines and changes to the signature of LSM hooks). This design imposes that the MAC policy (eBPF programs) be updated when the inspected kernel structures change outside of BTF compatibility guarantees. In practice, this is only required when a structure field used by a current policy is removed (or renamed) or when the used LSM hooks change. We expect the maintenance cost of these changes to be acceptable as compared to the previous design (https://lore.kernel.org/bpf/20190910115527.5235-1-kpsingh@chromium.org/). # Usage Examples A simple example and some documentation is included in the patchset. In order to better illustrate the capabilities of the framework some more advanced prototype (not-ready for review) code has also been published separately: * Logging execution events (including environment variables and arguments) https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_audit_env.c * Detecting deletion of running executables: https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_detect_exec_unlink.c * Detection of writes to /proc//mem: https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_audit_env.c We have updated Google's internal telemetry infrastructure and have started deploying this LSM on our Linux Workstations. This gives us more confidence in the real-world applications of such a system. KP Singh (8): bpf: Introduce BPF_PROG_TYPE_LSM security: Refactor declaration of LSM hooks bpf: lsm: provide attachment points for BPF LSM programs bpf: lsm: Add support for enabling/disabling BPF hooks bpf: lsm: Implement attach, detach and execution tools/libbpf: Add support for BPF_PROG_TYPE_LSM bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM bpf: lsm: Add Documentation Documentation/bpf/bpf_lsm.rst | 147 +++++ Documentation/bpf/index.rst | 1 + MAINTAINERS | 1 + arch/x86/net/bpf_jit_comp.c | 21 +- include/linux/bpf.h | 7 + include/linux/bpf_lsm.h | 66 ++ include/linux/bpf_types.h | 4 + include/linux/lsm_hook_names.h | 353 ++++++++++ include/linux/lsm_hooks.h | 622 +----------------- include/uapi/linux/bpf.h | 2 + init/Kconfig | 11 + kernel/bpf/Makefile | 1 + kernel/bpf/bpf_lsm.c | 88 +++ kernel/bpf/btf.c | 3 +- kernel/bpf/syscall.c | 47 +- kernel/bpf/trampoline.c | 24 +- kernel/bpf/verifier.c | 19 +- kernel/trace/bpf_trace.c | 12 +- security/security.c | 35 + tools/include/uapi/linux/bpf.h | 2 + tools/lib/bpf/bpf.c | 3 +- tools/lib/bpf/libbpf.c | 46 +- tools/lib/bpf/libbpf.h | 4 + tools/lib/bpf/libbpf.map | 3 + tools/lib/bpf/libbpf_probes.c | 1 + tools/testing/selftests/bpf/lsm_helpers.h | 19 + .../selftests/bpf/prog_tests/lsm_mprotect.c | 96 +++ .../selftests/bpf/progs/lsm_mprotect_audit.c | 48 ++ .../selftests/bpf/progs/lsm_mprotect_mac.c | 53 ++ 29 files changed, 1085 insertions(+), 654 deletions(-) create mode 100644 Documentation/bpf/bpf_lsm.rst create mode 100644 include/linux/bpf_lsm.h create mode 100644 include/linux/lsm_hook_names.h create mode 100644 kernel/bpf/bpf_lsm.c create mode 100644 tools/testing/selftests/bpf/lsm_helpers.h create mode 100644 tools/testing/selftests/bpf/prog_tests/lsm_mprotect.c create mode 100644 tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c create mode 100644 tools/testing/selftests/bpf/progs/lsm_mprotect_mac.c