linux/arch/sh/configs
David Hildenbrand bbcd53c960 drivers/char: remove /dev/kmem for good
Patch series "drivers/char: remove /dev/kmem for good".

Exploring /dev/kmem and /dev/mem in the context of memory hot(un)plug and
memory ballooning, I started questioning the existence of /dev/kmem.

Comparing it with the /proc/kcore implementation, it does not seem to be
able to deal with things like

a) Pages unmapped from the direct mapping (e.g., to be used by secretmem)
  -> kern_addr_valid(). virt_addr_valid() is not sufficient.

b) Special cases like gart aperture memory that is not to be touched
  -> mem_pfn_is_ram()

Unless I am missing something, it's at least broken in some cases and might
fault/crash the machine.

Looks like its existence has been questioned before in 2005 and 2010 [1],
after ~11 additional years, it might make sense to revive the discussion.

CONFIG_DEVKMEM is only enabled in a single defconfig (on purpose or by
mistake?).  All distributions disable it: in Ubuntu it has been disabled
for more than 10 years, in Debian since 2.6.31, in Fedora at least
starting with FC3, in RHEL starting with RHEL4, in SUSE starting from
15sp2, and OpenSUSE has it disabled as well.

1) /dev/kmem was popular for rootkits [2] before it got disabled
   basically everywhere. Ubuntu documents [3] "There is no modern user of
   /dev/kmem any more beyond attackers using it to load kernel rootkits.".
   RHEL documents in a BZ [5] "it served no practical purpose other than to
   serve as a potential security problem or to enable binary module drivers
   to access structures/functions they shouldn't be touching"

2) /proc/kcore is a decent interface to have a controlled way to read
   kernel memory for debugging puposes. (will need some extensions to
   deal with memory offlining/unplug, memory ballooning, and poisoned
   pages, though)

3) It might be useful for corner case debugging [1]. KDB/KGDB might be a
   better fit, especially, to write random memory; harder to shoot
   yourself into the foot.

4) "Kernel Memory Editor" [4] hasn't seen any updates since 2000 and seems
   to be incompatible with 64bit [1]. For educational purposes,
   /proc/kcore might be used to monitor value updates -- or older
   kernels can be used.

5) It's broken on arm64, and therefore, completely disabled there.

Looks like it's essentially unused and has been replaced by better
suited interfaces for individual tasks (/proc/kcore, KDB/KGDB). Let's
just remove it.

[1] https://lwn.net/Articles/147901/
[2] https://www.linuxjournal.com/article/10505
[3] https://wiki.ubuntu.com/Security/Features#A.2Fdev.2Fkmem_disabled
[4] https://sourceforge.net/projects/kme/
[5] https://bugzilla.redhat.com/show_bug.cgi?id=154796

Link: https://lkml.kernel.org/r/20210324102351.6932-1-david@redhat.com
Link: https://lkml.kernel.org/r/20210324102351.6932-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Alexander A. Klimov" <grandmaster@al2klimov.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Chris Zankel <chris@zankel.net>
Cc: Corentin Labbe <clabbe@baylibre.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Gregory Clement <gregory.clement@bootlin.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hillf Danton <hdanton@sina.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: James Troup <james.troup@canonical.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kairui Song <kasong@redhat.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: openrisc@lists.librecores.org
Cc: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: "Pavel Machek (CIP)" <pavel@denx.de>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Pierre Morel <pmorel@linux.ibm.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Rich Felker <dalias@libc.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: sparclinux@vger.kernel.org
Cc: Stafford Horne <shorne@gmail.com>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Theodore Dubois <tblodt@icloud.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: William Cohen <wcohen@redhat.com>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-07 00:26:34 -07:00
..
ap325rxa_defconfig arch/sh/configs: remove obsolete CONFIG_SOC_CAMERA* 2020-08-14 22:05:12 -04:00
apsh4a3a_defconfig sh: configs: Remove useless UEVENT_HELPER_PATH 2019-06-10 15:49:20 +09:00
apsh4ad0a_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
dreamcast_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
ecovec24-romimage_defconfig sh: configs: Remove useless UEVENT_HELPER_PATH 2019-06-10 15:49:20 +09:00
ecovec24_defconfig arch/sh/configs: remove obsolete CONFIG_SOC_CAMERA* 2020-08-14 22:05:12 -04:00
edosk7705_defconfig drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
edosk7760_defconfig module: remove EXPORT_UNUSED_SYMBOL* 2021-02-08 12:28:07 +01:00
espt_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
hp6xx_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
j2_defconfig sh: add earlycon support to j2_defconfig 2016-10-18 18:54:56 -04:00
kfr2r09-romimage_defconfig sh: configs: Remove useless UEVENT_HELPER_PATH 2019-06-10 15:49:20 +09:00
kfr2r09_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
landisk_defconfig sh: remove CONFIG_IDE from most defconfig 2021-01-06 19:55:25 -05:00
lboxre2_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
magicpanelr2_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
microdev_defconfig sh: remove CONFIG_IDE from most defconfig 2021-01-06 19:55:25 -05:00
migor_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
polaris_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
r7780mp_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
r7785rp_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
rsk7201_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
rsk7203_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
rsk7264_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
rsk7269_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
rts7751r2d1_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
rts7751r2dplus_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
sdk7780_defconfig Modules updates for v5.12 2021-02-23 10:15:33 -08:00
sdk7786_defconfig Remove oprofile and dcookies support 2021-02-21 10:40:34 -08:00
se7206_defconfig drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
se7343_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
se7619_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
se7705_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
se7712_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
se7721_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
se7722_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
se7724_defconfig arch/sh/configs: remove obsolete CONFIG_SOC_CAMERA* 2020-08-14 22:05:12 -04:00
se7750_defconfig sh: remove CONFIG_IDE from most defconfig 2021-01-06 19:55:25 -05:00
se7751_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
se7780_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
secureedge5410_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
sh03_defconfig Remove oprofile and dcookies support 2021-02-21 10:40:34 -08:00
sh2007_defconfig drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
sh7710voipgw_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
sh7724_generic_defconfig drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
sh7757lcr_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
sh7763rdp_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
sh7770_generic_defconfig drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
sh7785lcr_32bit_defconfig drivers/char: remove /dev/kmem for good 2021-05-07 00:26:34 -07:00
sh7785lcr_defconfig sh: configs: Remove useless UEVENT_HELPER_PATH 2019-06-10 15:49:20 +09:00
shmin_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
shx3_defconfig arch: sh: Remove CONFIG_OPROFILE support 2021-01-29 10:05:51 +05:30
titan_defconfig all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
ul2_defconfig sh: configs: Cleanup old Kconfig IO scheduler options 2020-06-01 14:48:48 -04:00
urquell_defconfig sh: configs: Remove useless UEVENT_HELPER_PATH 2019-06-10 15:49:20 +09:00