On Mon, Feb 08, 2021 at 02:12:00PM -0800, Kees Cook wrote: > On Fri, Feb 05, 2021 at 10:00:12PM +0000, Chris Wilson wrote: > > 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@xxxxxxxxxxxxxxxxxx> > > Thanks! > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Thanks for reviews&patch, I stuffed it into a topic branch and plan to send it to Linus later this week. Cheers, Daniel > > -Kees > > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > > Cc: Will Drewry <wad@xxxxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Dave Airlie <airlied@xxxxxxxxx> > > Cc: Daniel Vetter <daniel@xxxxxxxx> > > Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx> > > Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> > > Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx> # DRM depends on kcmp > > Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> # systemd uses kcmp > > > > --- > > v2: > > - Default n. > > - Borrrow help message from man kcmp. > > - Export get_epoll_tfile_raw_ptr() for CONFIG_KCMP > > v3: > > - Select KCMP for CONFIG_DRM > > --- > > drivers/gpu/drm/Kconfig | 3 +++ > > fs/eventpoll.c | 4 ++-- > > include/linux/eventpoll.h | 2 +- > > init/Kconfig | 11 +++++++++++ > > kernel/Makefile | 2 +- > > tools/testing/selftests/seccomp/seccomp_bpf.c | 2 +- > > 6 files changed, 19 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig > > index 0973f408d75f..af6c6d214d91 100644 > > --- a/drivers/gpu/drm/Kconfig > > +++ b/drivers/gpu/drm/Kconfig > > @@ -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 > > diff --git a/fs/eventpoll.c b/fs/eventpoll.c > > index a829af074eb5..3196474cbe24 100644 > > --- a/fs/eventpoll.c > > +++ b/fs/eventpoll.c > > @@ -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. > > diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h > > index 0350393465d4..593322c946e6 100644 > > --- a/include/linux/eventpoll.h > > +++ b/include/linux/eventpoll.h > > @@ -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 > > > > diff --git a/init/Kconfig b/init/Kconfig > > index b77c60f8b963..9cc7436b2f73 100644 > > --- a/init/Kconfig > > +++ b/init/Kconfig > > @@ -1194,6 +1194,7 @@ 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. > > @@ -1737,6 +1738,16 @@ 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 > > diff --git a/kernel/Makefile b/kernel/Makefile > > index aa7368c7eabf..320f1f3941b7 100644 > > --- a/kernel/Makefile > > +++ b/kernel/Makefile > > @@ -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 > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c > > index 26c72f2b61b1..1b6c7d33c4ff 100644 > > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c > > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c > > @@ -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) > > -- > > 2.20.1 > > > > -- > Kees Cook -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
