From patchwork Wed Jul 7 01:03:50 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Igor Zhbanov X-Patchwork-Id: 12361399 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97660C07E9C for ; Wed, 7 Jul 2021 01:10:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C8E961CAC for ; Wed, 7 Jul 2021 01:10:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230018AbhGGBNO (ORCPT ); Tue, 6 Jul 2021 21:13:14 -0400 Received: from mxout04.lancloud.ru ([45.84.86.114]:37018 "EHLO mxout04.lancloud.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229834AbhGGBNN (ORCPT ); Tue, 6 Jul 2021 21:13:13 -0400 X-Greylist: delayed 404 seconds by postgrey-1.27 at vger.kernel.org; Tue, 06 Jul 2021 21:13:13 EDT Received: from LanCloud DKIM-Filter: OpenDKIM Filter v2.11.0 mxout04.lancloud.ru 83D782099DE9 Received: from LanCloud Received: from LanCloud Received: from LanCloud To: linux-integrity , linux-security-module CC: Igor Zhbanov , Mimi Zohar From: Igor Zhbanov Subject: [PATCH 0/1] NAX (No Anonymous Execution) LSM Message-ID: Date: Wed, 7 Jul 2021 04:03:50 +0300 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 Content-Language: ru-RU X-Originating-IP: [192.168.11.198] X-ClientProxiedBy: LFEXT01.lancloud.ru (fd00:f066::141) To LFEX1909.lancloud.ru (fd00:f066::79) Precedence: bulk List-ID: [Overview] Fileless malware attacks are becoming more and more popular, and even ready-to-use frameworks are available [1], [2], [3]. They are based on running of the malware code from anonymous executable memory pages (which are not backed by an executable file or a library on a filesystem.) This allows effectively hiding malware presence in a system, making filesystem integrity checking tools unable to detect the intrusion. Typically, the malware first needs to intercept the execution flow (e.g., by the means of ROP-based exploit). Then it needs to download the main part (in the form of normal executable or library) from its server, because it is hard to implement the entire exploit in ROP-based form. There are a number of security mechanisms that can ensure the integrity of the file-system, but we need to ensure the integrity of the code in memory too, to be sure, that only authorized code is running in the system. The proposed LSM is preventing the creation of anonymous executable pages for the privileged processes. The LSM intercepts mmap() and mprotect() system calls and handles it similarly to SELinux handlers. The module allows to block the violating system call or to kill the violating process, along with rate-limited logging. Currently, the module restricts only the privileged processes. The privileged process is a process for which any of the following is true: + uid == 0 && !issecure(SECURE_NOROOT) + euid == 0 && !issecure(SECURE_NOROOT) + suid == 0 && !issecure(SECURE_NOROOT) + fsuid == 0 && !issecure(SECURE_NOROOT) + cap_effective has any capability except of kernel.nax.allowed_caps + cap_permitted has any capability except of kernel.nax.allowed_caps The sysctl parameter kernel.nax.allowed_caps allows to define safe capabilities set for the privileged processes. [JIT] Because of blocked anonymous code execution, JIT-compiled code, some interpreters (which are using JIT) and libffi-based projects can be broken. Our observation shows that such processes are typically running by a user, so they will not be privileged, so they will be allowed to use anonymous executable pages. But for small embedded set-ups it could be possible to get rid of such processes at all, so the module could be enabled without further restrictions to protect both privileged and non-privileged processes. In addition, libffi can be modified not to use anonymous executable pages. [Similar implementations] Although SELinux could be used to enable similar functionality, this LSM is simpler. It could be used in set-ups, where SELinux would be overkill. There is also SARA LSM module, which solves similar task, but it is more complex. [Cooperation with other security mechanisms] NAX LSM is more useful in conjunction with IMA. IMA would be responsible for integrity checking of file-based executables and libraries, and NAX LSM would be responsible for preventing of anonymous code execution. Alternatively, NAX LSM can be used with read-only root file system, protected by dm-verity/fs-verity. [TODO] - Implement xattrs support for marking privileged binaries on a per-file basis. - Store NAX attributes in the per-task LSM blob to implement special launchers for the privileged processes, so all of the children processes of such a launcher would be allowed to have anonymous executable pages (but not to grandchildren). [Links] [1] https://blog.fbkcs.ru/elf-in-memory-execution/ [2] https://magisterquis.github.io/2018/03/31/in-memory-only-elf-execution.html [3] https://www.prodefence.org/fireelf-fileless-linux-malware-framework/ P.S. I may continue to work on this LSM from my personal e-mail izh1979@gmail.com. Igor Zhbanov (1): NAX LSM: Add initial support support Documentation/admin-guide/LSM/NAX.rst | 48 ++++ Documentation/admin-guide/LSM/index.rst | 1 + security/Kconfig | 11 +- security/Makefile | 2 + security/nax/Kconfig | 71 +++++ security/nax/Makefile | 4 + security/nax/nax-lsm.c | 344 ++++++++++++++++++++++++ 7 files changed, 476 insertions(+), 5 deletions(-) create mode 100644 Documentation/admin-guide/LSM/NAX.rst create mode 100644 security/nax/Kconfig create mode 100644 security/nax/Makefile create mode 100644 security/nax/nax-lsm.c