[PATCH v5 0/6] Add support for O_MAYEXEC

Mickaël Salaün mic at digikod.net
Tue May 5 15:36:14 UTC 2020

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:
> 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.
> Previous version:
> https://lore.kernel.org/lkml/20200428175129.634352-1-mic@digikod.net/

The previous version (v4) is

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