2017-04-02 20:58:01 +00:00
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=====================================
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The Linux kernel user-space API guide
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=====================================
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.. _man-pages: https://www.kernel.org/doc/man-pages/
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While much of the kernel's user-space API is documented elsewhere
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(particularly in the man-pages_ project), some user-space information can
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also be found in the kernel tree itself. This manual is intended to be the
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place where this information is gathered.
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2024-01-22 22:18:30 +00:00
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System calls
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============
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2017-04-02 20:58:01 +00:00
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.. toctree::
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2024-01-22 22:18:30 +00:00
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:maxdepth: 1
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unshare
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futex2
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ebpf/index
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ioctl/index
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2024-04-15 16:35:23 +00:00
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mseal
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2024-01-22 22:18:30 +00:00
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Security-related interfaces
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===========================
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.. toctree::
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:maxdepth: 1
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2017-04-02 20:58:01 +00:00
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2017-05-13 11:51:38 +00:00
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no_new_privs
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2017-05-13 11:51:37 +00:00
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seccomp_filter
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2021-04-22 15:41:22 +00:00
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landlock
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2024-01-22 22:18:30 +00:00
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lsm
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mm/memfd: add documentation for MFD_NOEXEC_SEAL MFD_EXEC
When MFD_NOEXEC_SEAL was introduced, there was one big mistake: it didn't
have proper documentation. This led to a lot of confusion, especially
about whether or not memfd created with the MFD_NOEXEC_SEAL flag is
sealable. Before MFD_NOEXEC_SEAL, memfd had to explicitly set
MFD_ALLOW_SEALING to be sealable, so it's a fair question.
As one might have noticed, unlike other flags in memfd_create,
MFD_NOEXEC_SEAL is actually a combination of multiple flags. The idea is
to make it easier to use memfd in the most common way, which is NOEXEC +
F_SEAL_EXEC + MFD_ALLOW_SEALING. This works with sysctl vm.noexec to help
existing applications move to a more secure way of using memfd.
Proposals have been made to put MFD_NOEXEC_SEAL non-sealable, unless
MFD_ALLOW_SEALING is set, to be consistent with other flags [1], Those
are based on the viewpoint that each flag is an atomic unit, which is a
reasonable assumption. However, MFD_NOEXEC_SEAL was designed with the
intent of promoting the most secure method of using memfd, therefore a
combination of multiple functionalities into one bit.
Furthermore, the MFD_NOEXEC_SEAL has been added for more than one year,
and multiple applications and distributions have backported and utilized
it. Altering ABI now presents a degree of risk and may lead to
disruption.
MFD_NOEXEC_SEAL is a new flag, and applications must change their code to
use it. There is no backward compatibility problem.
When sysctl vm.noexec == 1 or 2, applications that don't set
MFD_NOEXEC_SEAL or MFD_EXEC will get MFD_NOEXEC_SEAL memfd. And
old-application might break, that is by-design, in such a system vm.noexec
= 0 shall be used. Also no backward compatibility problem.
I propose to include this documentation patch to assist in clarifying the
semantics of MFD_NOEXEC_SEAL, thereby preventing any potential future
confusion.
Finally, I would like to express my gratitude to David Rheinsberg and
Barnabás Pőcze for initiating the discussion on the topic of sealability.
[1]
https://lore.kernel.org/lkml/20230714114753.170814-1-david@readahead.eu/
[jeffxu@chromium.org: updates per Randy]
Link: https://lkml.kernel.org/r/20240611034903.3456796-2-jeffxu@chromium.org
[jeffxu@chromium.org: v3]
Link: https://lkml.kernel.org/r/20240611231409.3899809-2-jeffxu@chromium.org
Link: https://lkml.kernel.org/r/20240607203543.2151433-2-jeffxu@google.com
Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Barnabás Pőcze <pobrn@protonmail.com>
Cc: Daniel Verkamp <dverkamp@chromium.org>
Cc: David Rheinsberg <david@readahead.eu>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jorge Lucangeli Obes <jorgelo@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-06-07 20:35:41 +00:00
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mfd_noexec
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2018-04-29 13:20:11 +00:00
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spec_ctrl
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2024-01-22 22:18:30 +00:00
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tee
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Devices and I/O
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===============
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.. toctree::
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:maxdepth: 1
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2019-06-18 14:39:21 +00:00
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accelerators/ocxl
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2023-08-03 15:47:29 +00:00
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dma-buf-alloc-exchange
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2024-01-15 00:48:39 +00:00
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gpio/index
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2022-11-29 20:29:28 +00:00
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iommufd
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2020-03-10 12:57:48 +00:00
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media/index
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2024-01-22 22:18:30 +00:00
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dcdbas
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2021-08-31 10:36:34 +00:00
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vduse
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2023-12-21 12:48:15 +00:00
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isapnp
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2024-01-22 22:18:30 +00:00
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Everything else
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===============
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.. toctree::
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:maxdepth: 1
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ELF
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netlink/index
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sysfs-platform_profile
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2024-01-02 08:50:01 +00:00
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vduse
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futex2
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perf_ring_buffer
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2017-04-02 21:18:32 +00:00
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2017-04-02 20:58:01 +00:00
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.. only:: subproject and html
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Indices
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=======
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* :ref:`genindex`
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