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Date: Thu, 7 May 2020 10:36:41 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: David Laight <David.Laight@...LAB.COM>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: Aleksa Sarai <cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>, Andy Lutomirski <luto@...nel.org>,
Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Eric Chiang <ericchiang@...gle.com>, Florian Weimer <fweimer@...hat.com>,
James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>,
Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Mickaël Salaün <mickael.salaun@....gouv.fr>,
Mimi Zohar <zohar@...ux.ibm.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>,
Steve Grubb <sgrubb@...hat.com>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
"linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
"linux-security-module@...r.kernel.org"
<linux-security-module@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v5 0/6] Add support for O_MAYEXEC
On 07/05/2020 10:05, David Laight wrote:
> From: Mickaël Salaün
>> Sent: 05 May 2020 16:32
>>
>> This fifth patch series add new kernel configurations (OMAYEXEC_STATIC,
>> OMAYEXEC_ENFORCE_MOUNT, and OMAYEXEC_ENFORCE_FILE) to enable to
>> configure the security policy at kernel build time. As requested by
>> Mimi Zohar, I completed the series with one of her patches for IMA.
>>
>> The goal of this patch series is to enable to control script execution
>> with interpreters help. A new O_MAYEXEC flag, usable through
>> openat2(2), is added to enable userspace script interpreter to delegate
>> to the kernel (and thus the system security policy) the permission to
>> interpret/execute scripts or other files containing what can be seen as
>> commands.
>>
>> A simple system-wide security policy can be enforced by the system
>> administrator through a sysctl configuration consistent with the mount
>> points or the file access rights. The documentation patch explains the
>> prerequisites.
>>
>> Furthermore, the security policy can also be delegated to an LSM, either
>> a MAC system or an integrity system. For instance, the new kernel
>> MAY_OPENEXEC flag closes a major IMA measurement/appraisal interpreter
>> integrity gap by bringing the ability to check the use of scripts [1].
>> Other uses are expected, such as for openat2(2) [2], SGX integration
>> [3], bpffs [4] or IPE [5].
>>
>> Userspace needs to adapt to take advantage of this new feature. For
>> example, the PEP 578 [6] (Runtime Audit Hooks) enables Python 3.8 to be
>> extended with policy enforcement points related to code interpretation,
>> which can be used to align with the PowerShell audit features.
>> Additional Python security improvements (e.g. a limited interpreter
>> withou -c, stdin piping of code) are on their way.
>>
>> The initial idea come from CLIP OS 4 and the original implementation has
>> been used for more than 12 years:
>> https://github.com/clipos-archive/clipos4_doc
>>
>> An introduction to O_MAYEXEC was given at the Linux Security Summit
>> Europe 2018 - Linux Kernel Security Contributions by ANSSI:
>> https://www.youtube.com/watch?v=chNjCRtPKQY&t=17m15s
>> The "write xor execute" principle was explained at Kernel Recipes 2018 -
>> CLIP OS: a defense-in-depth OS:
>> https://www.youtube.com/watch?v=PjRE0uBtkHU&t=11m14s
>>
>> This patch series can be applied on top of v5.7-rc4. This can be tested
>> with CONFIG_SYSCTL. I would really appreciate constructive comments on
>> this patch series.
>
> None of that description actually says what the patch actually does.
"Add support for O_MAYEXEC" "to enable to control script execution".
What is not clear here? This seems well understood by other commenters.
The documentation patch and the talks can also help.
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