Commit bfe3911a authored by Chris Wilson's avatar Chris Wilson Committed by Daniel Vetter
Browse files

kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE 

Userspace has discovered the functionality offered by SYS_kcmp and has
started to depend upon it. In particular, Mesa uses SYS_kcmp for
os_same_file_description() in order to identify when two fd (e.g. device
or dmabuf) point to the same struct file. Since they depend on it for
core functionality, lift SYS_kcmp out of the non-default
CONFIG_CHECKPOINT_RESTORE into the selectable syscall category.

Rasmus Villemoes also pointed out that systemd uses SYS_kcmp to
deduplicate the per-service file descriptor store.

Note that some distributions such as Ubuntu are already enabling
CHECKPOINT_RESTORE in their configs and so, by extension, SYS_kcmp.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/3046


Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: stable@vger.kernel.org
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> # DRM depends on kcmp
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> # systemd uses kcmp
Reviewed-by: default avatarCyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205220012.1983-1-chris@chris-wilson.co.uk
parent f40ddce8

drivers/gpu/drm/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -15,6 +15,9 @@ menuconfig DRM 
	select I2C_ALGOBIT

	select DMA_SHARED_BUFFER

	select SYNC_FILE

# gallium uses SYS_kcmp for os_same_file_description() to de-duplicate

# device and dmabuf fd. Let's make sure that is available for our userspace.

	select KCMP

	help

	  Kernel-level support for the Direct Rendering Infrastructure (DRI)

	  introduced in XFree86 4.0. If you say Y here, you need to select

fs/eventpoll.c

+2 −2
Original line number Diff line number Diff line
@@ -979,7 +979,7 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) 
	return epir;

}



#ifdef CONFIG_CHECKPOINT_RESTORE

#ifdef CONFIG_KCMP

static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)

{

	struct rb_node *rbp;
@@ -1021,7 +1021,7 @@ struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, 


	return file_raw;

}

#endif /* CONFIG_CHECKPOINT_RESTORE */

#endif /* CONFIG_KCMP */



/**

 * Adds a new entry to the tail of the list in a lockless way, i.e.

include/linux/eventpoll.h

+1 −1
Original line number Diff line number Diff line
@@ -18,7 +18,7 @@ struct file; 


#ifdef CONFIG_EPOLL



#ifdef CONFIG_CHECKPOINT_RESTORE

#ifdef CONFIG_KCMP

struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long toff);

#endif

init/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -1193,6 +1193,7 @@ endif # NAMESPACES 
config CHECKPOINT_RESTORE

	bool "Checkpoint/restore support"

	select PROC_CHILDREN

	select KCMP

	default n

	help

	  Enables additional kernel features in a sake of checkpoint/restore.
@@ -1736,6 +1737,16 @@ config ARCH_HAS_MEMBARRIER_CALLBACKS 
config ARCH_HAS_MEMBARRIER_SYNC_CORE

	bool



config KCMP

	bool "Enable kcmp() system call" if EXPERT

	help

	  Enable the kernel resource comparison system call. It provides

	  user-space with the ability to compare two processes to see if they

	  share a common resource, such as a file descriptor or even virtual

	  memory space.



	  If unsure, say N.



config RSEQ

	bool "Enable rseq() system call" if EXPERT

	default y

kernel/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -51,7 +51,7 @@ obj-y += livepatch/ 
obj-y += dma/

obj-y += entry/



obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o

obj-$(CONFIG_KCMP) += kcmp.o

obj-$(CONFIG_FREEZER) += freezer.o

obj-$(CONFIG_PROFILING) += profile.o

obj-$(CONFIG_STACKTRACE) += stacktrace.o