From patchwork Tue Nov 21 18:26:03 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Salvatore Mesoraca X-Patchwork-Id: 10068683 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 3D14A6022E for ; Tue, 21 Nov 2017 18:27:02 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 33C0A283CA for ; Tue, 21 Nov 2017 18:27:02 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 283D1298AE; Tue, 21 Nov 2017 18:27:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, GAPPY_SUBJECT, RCVD_IN_DNSWL_MED, T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 9666C283CA for ; Tue, 21 Nov 2017 18:27:00 +0000 (UTC) Received: (qmail 30320 invoked by uid 550); 21 Nov 2017 18:26:46 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 30121 invoked from network); 21 Nov 2017 18:26:44 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=Gd2m93P+IeCBzFic9ULYpEwoJFUfgPPDYUFaxB5xZ0U=; b=KlikK0/mV/OC9yPN6xWmVs9RoL1hE4K6tEEE2W301BXHXIVUZDyV7XDRxgEXyn+wtH lwUDWywnFCY70q1OzkgPekL6J8byzeKjxc7jJdHgrNUXG8lC3sgUoaWa+9lPTt1Uy4cO 8D5mcPTmbixVxjfXLEizBdLz49xJIKmi6t2Niy2W4jFQG8pNtT6AcVkCU7jtCX3lcpWU McjGefKIvWs1IWMu+2rlkcEe6nSwn48PQ1wuwr/4PJpr5ZgE61KEFgT0uTfnWz6XqKNj ZGxBZphpZfTNJ+JKYknbx9Eug+f+QZFcKW5dIfMb0hRpJTQOu1pE2Y4aCbjTTVkLlsdF 4S0A== 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:in-reply-to :references; bh=Gd2m93P+IeCBzFic9ULYpEwoJFUfgPPDYUFaxB5xZ0U=; b=UiD8cMg6Et5FcoPC6hamlqR13HE9rzLDKaJ+WJlH6s33VGQNHQfBQ9zpMMG/TEmHM8 FAZMOIteRJA03GtfI0nvACbZQuBOl17c9CKF2c3Iud1CEGIeug2II/8OaOS5LkRdxMOd /+l5H4AgxwlZYIJAQ1mwPUUiEOPbvnaJ0a9FazO84R7gyESdLQGEO/kV8oMD3P/IKSkq JqRUSj9cR+qpgSJJWZP2YPcdTsRqbP2Ix7Fd9c20XJbAkRi32lBPZpD9nL/W/k6FENEG ig9gFrVxoR8VDwl6I3vt5v60oW5gMFf7v2hQOjIFKf7j/iN4g5ZxYOdDs+2LNaYBIzNS R2ig== X-Gm-Message-State: AJaThX7jUlUbW2X3Oe5c2KbTFz4xaIAvP88CRt8PdiK4a4Ihov+uRS1h SpFixbB3e5CaJHkrnFYYszc= X-Google-Smtp-Source: AGs4zMbWrL8FClQj+stgIG6+OttSpU6s4fF8TXnzmER0+htCplC4DWJ9Euk2O0Jv3hcIh9PXUCLEjg== X-Received: by 10.223.160.217 with SMTP id n25mr14909166wrn.27.1511288793308; Tue, 21 Nov 2017 10:26:33 -0800 (PST) From: Salvatore Mesoraca To: linux-kernel@vger.kernel.org Cc: linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, Salvatore Mesoraca , Alexander Viro , Brad Spengler , Casey Schaufler , Christoph Hellwig , James Morris , Jann Horn , Kees Cook , PaX Team , Thomas Gleixner , "Serge E. Hallyn" Date: Tue, 21 Nov 2017 19:26:03 +0100 Message-Id: <1511288772-19308-2-git-send-email-s.mesoraca16@gmail.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1511288772-19308-1-git-send-email-s.mesoraca16@gmail.com> References: <1511288772-19308-1-git-send-email-s.mesoraca16@gmail.com> Subject: [kernel-hardening] [RFC v4 01/10] S.A.R.A. Documentation X-Virus-Scanned: ClamAV using ClamSMTP Adding documentation for S.A.R.A. LSM. Signed-off-by: Salvatore Mesoraca --- Documentation/admin-guide/LSM/SARA.rst | 173 ++++++++++++++++++++++++ Documentation/admin-guide/LSM/index.rst | 1 + Documentation/admin-guide/kernel-parameters.txt | 24 ++++ 3 files changed, 198 insertions(+) create mode 100644 Documentation/admin-guide/LSM/SARA.rst diff --git a/Documentation/admin-guide/LSM/SARA.rst b/Documentation/admin-guide/LSM/SARA.rst new file mode 100644 index 0000000..de41b78 --- /dev/null +++ b/Documentation/admin-guide/LSM/SARA.rst @@ -0,0 +1,173 @@ +======== +S.A.R.A. +======== + +S.A.R.A. (S.A.R.A. is Another Recursive Acronym) is a stacked Linux Security +Module that aims to collect heterogeneous security measures, providing a common +interface to manage them. +As of today it consists of one submodule: + +- WX Protection + + +The kernel-space part is complemented by its user-space counterpart: `saractl` +[2]_. +A test suite for WX Protection, called `sara-test` [4]_, is also available. +More information about where to find these tools and the full S.A.R.A. +documentation are in the `External Links and Documentation`_ section. + +------------------------------------------------------------------------------- + +S.A.R.A.'s Submodules +===================== + +WX Protection +------------- +WX Protection aims to improve user-space programs security by applying: + +- `W^X enforcement`_ +- `W!->X (once writable never executable) mprotect restriction`_ +- `Executable MMAP prevention`_ + +All of the above features can be enabled or disabled both system wide +or on a per executable basis through the use of configuration files managed by +`saractl` [2]_. + +It is important to note that some programs may have issues working with +WX Protection. In particular: + +- **W^X enforcement** will cause problems to any programs that needs + memory pages mapped both as writable and executable at the same time e.g. + programs with executable stack markings in the *PT_GNU_STACK* segment. +- **W!->X mprotect restriction** will cause problems to any program that + needs to generate executable code at run time or to modify executable + pages e.g. programs with a *JIT* compiler built-in or linked against a + *non-PIC* library. +- **Executable MMAP prevention** can work only with programs that have at least + partial *RELRO* support. It's disabled automatically for programs that + lack this feature. It will cause problems to any program that uses *dlopen* + or tries to do an executable mmap. Unfortunately this feature is the one + that could create most problems and should be enabled only after careful + evaluation. + +To extend the scope of the above features, despite the issues that they may +cause, they are complemented by **/proc/PID/attr/sara/wxprot** interface +and **trampoline emulation**. + +At the moment, WX Protection (unless specified otherwise) should work on +any architecture supporting the NX bit, including, but not limited to: +`x86_64`, `x86_32` (with PAE), `ARM` and `ARM64`. + +Parts of WX Protection are inspired by some of the features available in PaX. + +For further information about configuration file format and user-space +utilities please take a look at the full documentation [1]_. + +W^X enforcement +^^^^^^^^^^^^^^^ +W^X means that a program can't have a page of memory that is marked, at the +same time, writable and executable. This also allow to detect many bad +behaviours that make life much more easy for attackers. Programs running with +this feature enabled will be more difficult to exploit in the case they are +affected by some vulnerabilities, because the attacker will be forced +to make more steps in order to exploit them. + +W!->X (once writable never executable) mprotect restriction +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +"Once writable never executable" means that any page that could have been +marked as writable in the past won't ever be allowed to be marked (e.g. via +an mprotect syscall) as executable. +This goes on the same track as W^X, but is much stricter and prevents +the runtime creation of new executable code in memory. +Obviously, this feature does not prevent a program from creating a new file and +*mmapping* it as executable, however, it will be way more difficult for +attackers to exploit vulnerabilities if this feature is enabled. + +Executable MMAP prevention +^^^^^^^^^^^^^^^^^^^^^^^^^^ +This feature prevents the creation of new executable mmaps after the dynamic +libraries have been loaded. When used in combination with **W!->X mprotect +restriction** this feature will completely prevent the creation of new +executable code from the current thread. +Obviously, this feature does not prevent cases in which an attacker uses an +*execve* to start a completely new program. This kind of restriction, if +needed, can be applied using one of the other LSM that focuses on MAC. +Please be aware that this feature can break many programs and so it should be +enabled after careful evaluation. + +/proc/PID/attr/sara/wxprot interface +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +The `procattr` interface can be used by a thread to discover which +WX Protection features are enabled and/or to tighten them: protection +can't be softened via procattr. +The interface is simple: it's a text file with an hexadecimal +number in it representing enabled features (more information can be +found in the `Flags values`_ section). Via this interface it is also +possible to perform a complete memory scan to remove the write permission +from pages that are both writable and executable, please note that this +change will also affect other threads of the same process. + +Protections that prevent the runtime creation of executable code +can be troublesome for all those programs that actually need to do it +e.g. programs shipping with a JIT compiler built-in. +This feature can be use to run the JIT compiler with few restrictions +while enforcing full WX Protection in the rest of the program. + +The preferred way to access this interface is via `libsara` [3]_. +If you don't want it as a dependency, you can just statically link it +in your project or copy/paste parts of it. +To make things simpler `libsara` is the only part of S.A.R.A. released under +*CC0 - No Rights Reserved* license. + +Trampoline emulation +^^^^^^^^^^^^^^^^^^^^ +Some programs need to generate part of their code at runtime. Luckily enough, +in some cases they only generate well-known code sequences (the +*trampolines*) that can be easily recognized and emulated by the kernel. +This way WX Protection can still be active, so a potential attacker won't be +able to generate arbitrary sequences of code, but just those that are +explicitly allowed. This is not ideal, but it's still better than having WX +Protection completely disabled. + +In particular S.A.R.A. is able to recognize trampolines used by GCC for nested +C functions and libffi's trampolines. +This feature is available only on `x86_32` and `x86_64`. + +Flags values +^^^^^^^^^^^^ +Flags are represented as a 16 bit unsigned integer in which every bit indicates +the status of a given feature: + ++------------------------------+----------+ +| Feature | Value | ++==============================+==========+ +| W!->X Heap | 0x0001 | ++------------------------------+----------+ +| W!->X Stack | 0x0002 | ++------------------------------+----------+ +| W!->X Other memory | 0x0004 | ++------------------------------+----------+ +| W^X | 0x0008 | ++------------------------------+----------+ +| Don't enforce, just complain | 0x0010 | ++------------------------------+----------+ +| Be Verbose | 0x0020 | ++------------------------------+----------+ +| Executable MMAP prevention | 0x0040 | ++------------------------------+----------+ +| Force W^X on setprocattr | 0x0080 | ++------------------------------+----------+ +| Trampoline emulation | 0x0100 | ++------------------------------+----------+ +| Children will inherit flags | 0x0200 | ++------------------------------+----------+ + +------------------------------------------------------------------------------- + +External Links and Documentation +================================ + +.. [1] `Documentation `_ +.. [2] `saractl `_ +.. [3] `libsara `_ +.. [4] `sara-test `_ diff --git a/Documentation/admin-guide/LSM/index.rst b/Documentation/admin-guide/LSM/index.rst index c980dfe..c0ae6bb3 100644 --- a/Documentation/admin-guide/LSM/index.rst +++ b/Documentation/admin-guide/LSM/index.rst @@ -39,3 +39,4 @@ the one "major" module (e.g. SELinux) if there is one configured. Smack tomoyo Yama + SARA diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 62436bd..20c9114 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3817,6 +3817,30 @@ 1 -- enable. Default value is set via kernel config option. + sara.enabled= [SARA] Disable or enable S.A.R.A. at boot time. + If disabled this way S.A.R.A. can't be enabled + again. + Format: { "0" | "1" } + See security/sara/Kconfig help text + 0 -- disable. + 1 -- enable. + Default value is set via kernel config option. + + sara.wxprot_enabled= [SARA] + Disable or enable S.A.R.A. WX Protection + at boot time. + Format: { "0" | "1" } + See security/sara/Kconfig help text + 0 -- disable. + 1 -- enable. + Default value is set via kernel config option. + + sara.wxprot_default_flags= [SARA] + Set S.A.R.A. WX Protection default flags. + Format: + See S.A.R.A. documentation. + Default value is set via kernel config option. + serialnumber [BUGS=X86-32] shapers= [NET]