On 06/05/2020 15:58, Lev R. Oshvang . wrote: > On Tue, May 5, 2020 at 6:36 PM Mickaël Salaün <mic@xxxxxxxxxxx> wrote: >> >> >> On 05/05/2020 17:31, Mickaël Salaün wrote: >>> Hi, >>> >>> 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. >>> >>> Previous version: >>> https://lore.kernel.org/lkml/20200428175129.634352-1-mic@xxxxxxxxxxx/ >> >> The previous version (v4) is >> https://lore.kernel.org/lkml/20200430132320.699508-1-mic@xxxxxxxxxxx/ > > > 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 >
