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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: Chris 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: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205220012.1983-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2021-02-05 22:00:12 +00:00 committed by Daniel Vetter
parent f40ddce885
commit bfe3911a91
6 changed files with 19 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/gpu/drm/Kconfig
View File

@ -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

4
fs/eventpoll.c
View File

@ -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.

2
include/linux/eventpoll.h
View File

@ -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

11
init/Kconfig
View File

@ -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

2
kernel/Makefile
View File

@ -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

2
tools/testing/selftests/seccomp/seccomp_bpf.c
View File

@ -315,7 +315,7 @@ TEST(kcmp)
ret = __filecmp(getpid(), getpid(), 1, 1);
EXPECT_EQ(ret, 0);
if (ret != 0 && errno == ENOSYS)
SKIP(return, "Kernel does not support kcmp() (missing CONFIG_CHECKPOINT_RESTORE?)");
SKIP(return, "Kernel does not support kcmp() (missing CONFIG_KCMP?)");
}
TEST(mode_strict_support)