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Message-ID: <86c3fdf8-bc00-8868-1ff1-96e6e1ca9203@digikod.net>
Date: Tue, 30 Nov 2021 11:35:00 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Alejandro Colomar <alx.manpages@...il.com>,
Aleksa Sarai <cyphar@...har.com>, Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Casey Schaufler <casey@...aufler-ca.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Christian Heimes <christian@...hon.org>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Dmitry Vyukov <dvyukov@...gle.com>, Eric Biggers <ebiggers@...nel.org>,
Eric Chiang <ericchiang@...gle.com>, Florian Weimer <fweimer@...hat.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>, 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>,
"Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>,
Miklos Szeredi <mszeredi@...hat.com>, Mimi Zohar <zohar@...ux.ibm.com>,
Paul Moore <paul@...l-moore.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.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>,
Yin Fengwei <fengwei.yin@...el.com>, kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: Re: [PATCH v17 0/3] Add trusted_for(2) (was O_MAYEXEC)
Hello Al,
I think there is no more comment on this series, everything has been
addressed. Could you please consider to merge this into your tree or
push it to linux-next?
Regards,
Mickaël
On 15/11/2021 19:53, Mickaël Salaün wrote:
> Hi,
>
> This new patch series fix the syscall signature as suggested by
> Alejandro Colomar. It applies on Linus's master branch (v5.16-rc1) and
> next-20211115.
>
> Andrew, can you please consider to merge this into your tree?
>
> Overview
> ========
>
> The final goal of this patch series is to enable the kernel to be a
> global policy manager by entrusting processes with access control at
> their level. To reach this goal, two complementary parts are required:
> * user space needs to be able to know if it can trust some file
> descriptor content for a specific usage;
> * and the kernel needs to make available some part of the policy
> configured by the system administrator.
>
> Primary goal of trusted_for(2)
> ==============================
>
> This new syscall enables user space to ask the kernel: is this file
> descriptor's content trusted to be used for this purpose? The set of
> usage currently only contains execution, but other may follow (e.g.
> configuration, sensitive data). If the kernel identifies the file
> descriptor as trustworthy for this usage, user space should then take
> this information into account. The "execution" usage means that the
> content of the file descriptor is trusted according to the system policy
> to be executed by user space, which means that it interprets the content
> or (try to) maps it as executable memory.
>
> A simple system-wide security policy can be set by the system
> administrator through a sysctl configuration consistent with the mount
> points or the file access rights. The documentation explains the
> prerequisites.
>
> It is important to note that this can only enable to extend access
> control managed by the kernel. Hence it enables current access control
> mechanism to be extended and become a superset of what they can
> currently control. Indeed, the security policy could also be delegated
> to an LSM, either a MAC system or an integrity system. For instance,
> this is required to close 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 magic-links [2], SGX integration
> [3], bpffs [4].
>
> Complementary W^X protections can be brought by SELinux, IPE [5] and
> trampfd [6].
>
> System call description
> =======================
>
> trusted_for(int fd, enum trusted_for_usage usage, u32 flags);
>
> @fd is the file descriptor to check.
>
> @usage identifies the user space usage intended for @fd: only
> TRUSTED_FOR_EXECUTION for now, but trusted_for_usage could be extended
> to identify other usages (e.g. configuration, sensitive data).
>
> @flags must be 0 for now but it could be used in the future to do
> complementary checks (e.g. signature or integrity requirements, origin
> of the file).
>
> This system call returns 0 on success, or -EACCES if the kernel policy
> denies the specified usage (which should be enforced by the caller).
>
> The first patch contains the full syscall and sysctl documentation.
>
> Prerequisite of its use
> =======================
>
> User space needs to adapt to take advantage of this new feature. For
> example, the PEP 578 [7] (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
> without -c, stdin piping of code) are on their way [8].
>
> Examples
> ========
>
> The initial idea comes from CLIP OS 4 and the original implementation
> has been used for more than 13 years:
> https://github.com/clipos-archive/clipos4_doc
> Chrome OS has a similar approach:
> https://chromium.googlesource.com/chromiumos/docs/+/master/security/noexec_shell_scripts.md
>
> Userland patches can be found here:
> https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC
> Actually, there is more than the O_MAYEXEC changes (which matches this search)
> e.g., to prevent Python interactive execution. There are patches for
> Bash, Wine, Java (Icedtea), Busybox's ash, Perl and Python. There are
> also some related patches which do not directly rely on O_MAYEXEC but
> which restrict the use of browser plugins and extensions, which may be
> seen as scripts too:
> https://github.com/clipos-archive/clipos4_portage-overlay/tree/master/www-client
>
> 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
> See also a first LWN article about O_MAYEXEC and a new one about
> trusted_for(2) and its background:
> * https://lwn.net/Articles/820000/
> * https://lwn.net/Articles/832959/
>
> This can be tested with CONFIG_SYSCTL. I would really appreciate
> constructive comments on this patch series.
>
> [1] https://lore.kernel.org/lkml/20211014130125.6991-1-zohar@linux.ibm.com/
> [2] https://lore.kernel.org/lkml/20190904201933.10736-6-cyphar@cyphar.com/
> [3] https://lore.kernel.org/lkml/CALCETrVovr8XNZSroey7pHF46O=kj_c5D9K8h=z2T_cNrpvMig@mail.gmail.com/
> [4] https://lore.kernel.org/lkml/CALCETrVeZ0eufFXwfhtaG_j+AdvbzEWE0M3wjXMWVEO7pj+xkw@mail.gmail.com/
> [5] https://lore.kernel.org/lkml/20200406221439.1469862-12-deven.desai@linux.microsoft.com/
> [6] https://lore.kernel.org/lkml/20200922215326.4603-1-madvenka@linux.microsoft.com/
> [7] https://www.python.org/dev/peps/pep-0578/
> [8] https://lore.kernel.org/lkml/0c70debd-e79e-d514-06c6-4cd1e021fa8b@python.org/
>
> Previous versions:
> v16: https://lore.kernel.org/r/20211110190626.257017-1-mic@digikod.net/
> v15: https://lore.kernel.org/r/20211012192410.2356090-1-mic@digikod.net/
> v14: https://lore.kernel.org/r/20211008104840.1733385-1-mic@digikod.net/
> v13: https://lore.kernel.org/r/20211007182321.872075-1-mic@digikod.net/
> v12: https://lore.kernel.org/r/20201203173118.379271-1-mic@digikod.net/
> v11: https://lore.kernel.org/r/20201019164932.1430614-1-mic@digikod.net/
> v10: https://lore.kernel.org/r/20200924153228.387737-1-mic@digikod.net/
> v9: https://lore.kernel.org/r/20200910164612.114215-1-mic@digikod.net/
> v8: https://lore.kernel.org/r/20200908075956.1069018-1-mic@digikod.net/
> v7: https://lore.kernel.org/r/20200723171227.446711-1-mic@digikod.net/
> v6: https://lore.kernel.org/r/20200714181638.45751-1-mic@digikod.net/
> v5: https://lore.kernel.org/r/20200505153156.925111-1-mic@digikod.net/
> v4: https://lore.kernel.org/r/20200430132320.699508-1-mic@digikod.net/
> v3: https://lore.kernel.org/r/20200428175129.634352-1-mic@digikod.net/
> v2: https://lore.kernel.org/r/20190906152455.22757-1-mic@digikod.net/
> v1: https://lore.kernel.org/r/20181212081712.32347-1-mic@digikod.net/
>
> Regards,
>
> Mickaël Salaün (3):
> fs: Add trusted_for(2) syscall implementation and related sysctl
> arch: Wire up trusted_for(2)
> selftest/interpreter: Add tests for trusted_for(2) policies
>
> Documentation/admin-guide/sysctl/fs.rst | 50 +++
> arch/alpha/kernel/syscalls/syscall.tbl | 2 +
> arch/arm/tools/syscall.tbl | 1 +
> arch/arm64/include/asm/unistd.h | 2 +-
> arch/arm64/include/asm/unistd32.h | 2 +
> arch/ia64/kernel/syscalls/syscall.tbl | 2 +
> arch/m68k/kernel/syscalls/syscall.tbl | 2 +
> arch/microblaze/kernel/syscalls/syscall.tbl | 2 +
> arch/mips/kernel/syscalls/syscall_n32.tbl | 2 +
> arch/mips/kernel/syscalls/syscall_n64.tbl | 2 +
> arch/mips/kernel/syscalls/syscall_o32.tbl | 2 +
> arch/parisc/kernel/syscalls/syscall.tbl | 2 +
> arch/powerpc/kernel/syscalls/syscall.tbl | 2 +
> arch/s390/kernel/syscalls/syscall.tbl | 2 +
> arch/sh/kernel/syscalls/syscall.tbl | 2 +
> arch/sparc/kernel/syscalls/syscall.tbl | 2 +
> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> arch/xtensa/kernel/syscalls/syscall.tbl | 2 +
> fs/open.c | 111 ++++++
> include/linux/fs.h | 1 +
> include/linux/syscalls.h | 1 +
> include/uapi/asm-generic/unistd.h | 4 +-
> include/uapi/linux/trusted-for.h | 18 +
> kernel/sysctl.c | 12 +-
> tools/testing/selftests/Makefile | 1 +
> .../testing/selftests/interpreter/.gitignore | 2 +
> tools/testing/selftests/interpreter/Makefile | 21 +
> tools/testing/selftests/interpreter/config | 1 +
> .../selftests/interpreter/trust_policy_test.c | 362 ++++++++++++++++++
> 30 files changed, 613 insertions(+), 4 deletions(-)
> create mode 100644 include/uapi/linux/trusted-for.h
> create mode 100644 tools/testing/selftests/interpreter/.gitignore
> create mode 100644 tools/testing/selftests/interpreter/Makefile
> create mode 100644 tools/testing/selftests/interpreter/config
> create mode 100644 tools/testing/selftests/interpreter/trust_policy_test.c
>
>
> base-commit: 8ab774587903771821b59471cc723bba6d893942
>
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