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![David Hildenbrand](/assets/img/avatar_default.png)
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 Looks like it's essentially unused and has been replaced by better suited interfaces for individual tasks (/proc/kcore, KDB/KGDB).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>
106 lines
2.9 KiB
Text
106 lines
2.9 KiB
Text
CONFIG_NO_HZ_IDLE=y
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CONFIG_HIGH_RES_TIMERS=y
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CONFIG_LOG_BUF_SHIFT=16
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CONFIG_CC_OPTIMIZE_FOR_SIZE=y
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CONFIG_EXPERT=y
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# CONFIG_UID16 is not set
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# CONFIG_BASE_FULL is not set
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# CONFIG_FUTEX is not set
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# CONFIG_EPOLL is not set
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# CONFIG_SIGNALFD is not set
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# CONFIG_EVENTFD is not set
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# CONFIG_AIO is not set
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# CONFIG_VM_EVENT_COUNTERS is not set
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# CONFIG_SLUB_DEBUG is not set
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# CONFIG_BLOCK is not set
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# CONFIG_MMU is not set
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CONFIG_ARCH_MPS2=y
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CONFIG_SET_MEM_PARAM=y
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CONFIG_DRAM_BASE=0x21000000
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CONFIG_DRAM_SIZE=0x1000000
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CONFIG_PREEMPT_VOLUNTARY=y
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# CONFIG_ATAGS is not set
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CONFIG_ZBOOT_ROM_TEXT=0x0
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CONFIG_ZBOOT_ROM_BSS=0x0
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CONFIG_BINFMT_FLAT=y
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CONFIG_BINFMT_SHARED_FLAT=y
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# CONFIG_COREDUMP is not set
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# CONFIG_SUSPEND is not set
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CONFIG_NET=y
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CONFIG_PACKET=y
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CONFIG_UNIX=y
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CONFIG_INET=y
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CONFIG_IP_PNP=y
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CONFIG_IP_PNP_DHCP=y
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# CONFIG_INET_XFRM_MODE_TRANSPORT is not set
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# CONFIG_INET_XFRM_MODE_TUNNEL is not set
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# CONFIG_INET_XFRM_MODE_BEET is not set
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# CONFIG_INET_DIAG is not set
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# CONFIG_IPV6 is not set
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# CONFIG_WIRELESS is not set
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CONFIG_DEVTMPFS=y
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CONFIG_DEVTMPFS_MOUNT=y
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# CONFIG_FW_LOADER is not set
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CONFIG_NETDEVICES=y
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# CONFIG_NET_CORE is not set
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# CONFIG_NET_VENDOR_ARC is not set
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# CONFIG_NET_CADENCE is not set
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# CONFIG_NET_VENDOR_BROADCOM is not set
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# CONFIG_NET_VENDOR_CIRRUS is not set
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# CONFIG_NET_VENDOR_EZCHIP is not set
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# CONFIG_NET_VENDOR_FARADAY is not set
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# CONFIG_NET_VENDOR_HISILICON is not set
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# CONFIG_NET_VENDOR_INTEL is not set
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# CONFIG_NET_VENDOR_MARVELL is not set
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# CONFIG_NET_VENDOR_MICREL is not set
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# CONFIG_NET_VENDOR_NATSEMI is not set
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# CONFIG_NET_VENDOR_QUALCOMM is not set
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# CONFIG_NET_VENDOR_RENESAS is not set
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# CONFIG_NET_VENDOR_ROCKER is not set
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# CONFIG_NET_VENDOR_SAMSUNG is not set
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# CONFIG_NET_VENDOR_SEEQ is not set
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CONFIG_SMSC911X=y
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# CONFIG_NET_VENDOR_STMICRO is not set
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# CONFIG_NET_VENDOR_VIA is not set
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# CONFIG_NET_VENDOR_WIZNET is not set
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# CONFIG_WLAN is not set
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# CONFIG_INPUT is not set
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# CONFIG_SERIO is not set
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# CONFIG_VT is not set
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# CONFIG_LEGACY_PTYS is not set
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CONFIG_SERIAL_NONSTANDARD=y
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CONFIG_SERIAL_MPS2_UART_CONSOLE=y
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CONFIG_SERIAL_MPS2_UART=y
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# CONFIG_HW_RANDOM is not set
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# CONFIG_HWMON is not set
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CONFIG_WATCHDOG=y
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CONFIG_ARM_SP805_WATCHDOG=y
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CONFIG_MFD_SYSCON=y
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# CONFIG_USB_SUPPORT is not set
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CONFIG_NEW_LEDS=y
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CONFIG_LEDS_CLASS=y
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CONFIG_LEDS_SYSCON=y
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CONFIG_LEDS_TRIGGERS=y
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CONFIG_LEDS_TRIGGER_TIMER=y
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CONFIG_LEDS_TRIGGER_ONESHOT=y
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CONFIG_LEDS_TRIGGER_HEARTBEAT=y
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CONFIG_LEDS_TRIGGER_BACKLIGHT=y
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CONFIG_LEDS_TRIGGER_CPU=y
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CONFIG_LEDS_TRIGGER_DEFAULT_ON=y
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CONFIG_ARM_TIMER_SP804=y
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# CONFIG_DNOTIFY is not set
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# CONFIG_INOTIFY_USER is not set
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# CONFIG_MISC_FILESYSTEMS is not set
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CONFIG_NFS_FS=y
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CONFIG_NFS_V4=y
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CONFIG_NFS_V4_1=y
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CONFIG_NFS_V4_2=y
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CONFIG_ROOT_NFS=y
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CONFIG_NLS=y
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CONFIG_PRINTK_TIME=y
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CONFIG_DEBUG_INFO=y
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# CONFIG_ENABLE_MUST_CHECK is not set
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CONFIG_DEBUG_FS=y
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# CONFIG_SCHED_DEBUG is not set
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# CONFIG_DEBUG_BUGVERBOSE is not set
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CONFIG_MEMTEST=y
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