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Date: Thu, 7 May 2020 10:30:04 +0200
From: Mickaël Salaün <>
To: "Lev R. Oshvang ." <>
Cc:, Aleksa Sarai <>,
 Alexei Starovoitov <>, Al Viro <>,
 Andy Lutomirski <>, Christian Heimes <>,
 Daniel Borkmann <>,
 Deven Bowers <>,
 Eric Chiang <>, Florian Weimer <>,
 James Morris <>, Jan Kara <>,
 Jann Horn <>, Jonathan Corbet <>,
 Kees Cook <>,
 Lakshmi Ramasubramanian <>,
 Matthew Garrett <>, Matthew Wilcox <>,
 Michael Kerrisk <>,
 Mickaël Salaün <>,
 Mimi Zohar <>,
 Philippe Trébuchet <>,
 Scott Shell <>,
 Sean Christopherson <>,
 Shuah Khan <>, Steve Dower <>,
 Steve Grubb <>,
 Thibaut Sautereau <>,
 Vincent Strubel <>,,,,
 LSM List <>,
Subject: Re: [PATCH v5 0/6] Add support for O_MAYEXEC

On 06/05/2020 15:58, Lev R. Oshvang . wrote:
> On Tue, May 5, 2020 at 6:36 PM Mickaël Salaün <> wrote:
>> On 05/05/2020 17:31, Mickaël Salaün wrote:
>>> Hi,
>>> This fifth patch series add new kernel configurations (OMAYEXEC_STATIC,
>>> 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:
>>> An introduction to O_MAYEXEC was given at the Linux Security Summit
>>> Europe 2018 - Linux Kernel Security Contributions by ANSSI:
>>> The "write xor execute" principle was explained at Kernel Recipes 2018 -
>>> CLIP OS: a defense-in-depth OS:
>>> 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.
>>> Previous version:
>> The previous version (v4) is
> Hi Michael
> I have couple of question
> 1. Why you did not add O_MAYEXEC to open()?
> Some time ago (around v4.14) open() did not return EINVAL when
> VALID_OPEN_FLAGS check failed.
> Now it does, so I do not see a problem that interpreter will use
> simple open(),  ( Although that path might be manipulated, but file
> contents will be verified by IMA)

Aleksa replied to this.

> 2. When you apply a new flag to mount, it means that IMA will check
> all files under this mount and it does not matter whether the file in
> question is a script or not.
> IMHO it is too hard overhead for performance reasons.

This patch series doesn't change the way IMA handles mount points.

> Regards,
> LEv

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