linux-kernel - [PATCH v4 0/5] sysctl: encode the min/max values directly in the table entry

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Message-Id: <cover.1726910671.git.wen.yang@linux.dev>
Date: Sat, 21 Sep 2024 17:28:59 +0800
From: Wen Yang <wen.yang@...ux.dev>
To: "Eric W . Biederman" <ebiederm@...ssion.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Joel Granados <j.granados@...sung.com>
Cc: Christian Brauner <brauner@...nel.org>,
	Thomas Weißschuh <thomas@...ch.de>,
	linux-kernel@...r.kernel.org,
	Wen Yang <wen.yang@...ux.dev>
Subject: [PATCH v4 0/5] sysctl: encode the min/max values directly in the table entry

Many modules use these additional static/global variables (such as
two_five_five, n_65535, ue_int_max, etc.) in the boundary checking of
sysctl, and they are read-only and never changed.

Eric points out: "by turning .extra1 and .extra2 into longs instead of
keeping them as pointers and needing constants to be pointed at somewhere
.. The only people I can see who find a significant benefit by
consolidating all of the constants into one place are people who know how
to stomp kernel memory."

This patch series achieves direct encoding values in table entries and still
maintains compatibility with existing extra1/extra2 pointers.
Afterwards, we can remove these unnecessary static variables progressively and
also gradually kill the shared const array.

v3: https://lore.kernel.org/all/cover.1726365007.git.wen.yang@linux.dev/
v2: https://lore.kernel.org/all/tencent_143077FB953D8B549153BB07F54C5AA4870A@qq.com/
v1: https://lore.kernel.org/all/tencent_95D22FF919A42A99DA3C886B322CBD983905@qq.com/

Wen Yang (5):
  sysctl: add helper functions to extract table->extra1/extra2
  sysctl: support encoding values directly in the table entry
  sysctl: add kunit test code to check the min/max encoding of sysctl
    table entries
  sysctl: delete mmap_rnd_bits_{min/max} and
    mmap_rnd_compat_bits_{min/max} to save 16 bytes
  sysctl: delete six_hundred_forty_kb to save 4 bytes

 fs/proc/proc_sysctl.c  |  29 +-
 include/linux/mm.h     |   4 -
 include/linux/sysctl.h |  64 ++++-
 kernel/sysctl-test.c   | 581 +++++++++++++++++++++++++++++++++++++++++
 kernel/sysctl.c        |  45 ++--
 mm/mmap.c              |   4 -
 6 files changed, 677 insertions(+), 50 deletions(-)

-- 
2.25.1