diff mbox series

[v3] kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE

Message ID 20210205220012.1983-1-chris@chris-wilson.co.uk
State Accepted
Commit bfe3911a91047557eb0e620f95a370aee6a248c7
Headers show
Series [v3] kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE | expand

Commit Message

Chris Wilson Feb. 5, 2021, 10 p.m. UTC
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

---
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(-)

Comments

Kees Cook Feb. 8, 2021, 10:12 p.m. UTC | #1
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@chris-wilson.co.uk>

Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> 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
> 
> ---
> 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
>
Emil Velikov Feb. 12, 2021, 12:57 p.m. UTC | #2
On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@chris-wilson.co.uk> 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)

As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
While you mention the CONFIG issue, there is also a portability aspect
(mesa runs on more than just linux) and as well as sandbox filtering
of the extra syscall.

Last time I looked, the latter was still an issue and mesa was using
SYS_kcmp to compare device node fds.
A far shorter and more portable solution is possible, so let me
prepare a Mesa patch.

-Emil
Simon Ser Feb. 12, 2021, 1:14 p.m. UTC | #3
On Friday, February 12th, 2021 at 1:57 PM, Emil Velikov <emil.l.velikov@gmail.com> wrote:

> On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@chris-wilson.co.uk> 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)
>
> As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
> While you mention the CONFIG issue, there is also a portability aspect
> (mesa runs on more than just linux) and as well as sandbox filtering
> of the extra syscall.
>
> Last time I looked, the latter was still an issue and mesa was using
> SYS_kcmp to compare device node fds.
> A far shorter and more portable solution is possible, so let me
> prepare a Mesa patch.

Comparing two DMA-BUFs can be done with their inode number, I think.

Comparing two device FDs is more subtle, because of GEM handle
ref'counting. You sometimes really want to check whether two FDs are
backed by the same file *description*. See [1] for details.

[1]: https://gitlab.freedesktop.org/mesa/drm/-/merge_requests/110
Michel Dänzer Feb. 12, 2021, 2:01 p.m. UTC | #4
On 2021-02-12 1:57 p.m., Emil Velikov wrote:
> On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@chris-wilson.co.uk> 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)
> 
> As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
> While you mention the CONFIG issue, there is also a portability aspect
> (mesa runs on more than just linux) and as well as sandbox filtering
> of the extra syscall.
> 
> Last time I looked, the latter was still an issue and mesa was using
> SYS_kcmp to compare device node fds.
> A far shorter and more portable solution is possible, so let me
> prepare a Mesa patch.

Make sure to read my comments on 
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6881 first. :)
Emil Velikov Feb. 12, 2021, 2:07 p.m. UTC | #5
On Fri, 12 Feb 2021 at 13:14, Simon Ser <contact@emersion.fr> wrote:
>
> On Friday, February 12th, 2021 at 1:57 PM, Emil Velikov <emil.l.velikov@gmail.com> wrote:
>
> > On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@chris-wilson.co.uk> 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)
> >
> > As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
> > While you mention the CONFIG issue, there is also a portability aspect
> > (mesa runs on more than just linux) and as well as sandbox filtering
> > of the extra syscall.
> >
> > Last time I looked, the latter was still an issue and mesa was using
> > SYS_kcmp to compare device node fds.
> > A far shorter and more portable solution is possible, so let me
> > prepare a Mesa patch.
>
> Comparing two DMA-BUFs can be done with their inode number, I think.
>
> Comparing two device FDs is more subtle, because of GEM handle
> ref'counting. You sometimes really want to check whether two FDs are
> backed by the same file *description*. See [1] for details.
>
Thanks for the correction and the reference.
Seems like I've short circuited file description table vs file descriptor.

Emil
Emil Velikov Feb. 12, 2021, 2:09 p.m. UTC | #6
On Fri, 12 Feb 2021 at 14:01, Michel Dänzer <michel@daenzer.net> wrote:
>
> On 2021-02-12 1:57 p.m., Emil Velikov wrote:
> > On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@chris-wilson.co.uk> 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)
> >
> > As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
> > While you mention the CONFIG issue, there is also a portability aspect
> > (mesa runs on more than just linux) and as well as sandbox filtering
> > of the extra syscall.
> >
> > Last time I looked, the latter was still an issue and mesa was using
> > SYS_kcmp to compare device node fds.
> > A far shorter and more portable solution is possible, so let me
> > prepare a Mesa patch.
>
> Make sure to read my comments on
> https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6881 first. :)
>
Much appreciated. I might have been "slightly" off - pardon for the noise o/

-Emil
Thomas Zimmermann Feb. 15, 2021, 8:56 a.m. UTC | #7
Hi

Am 05.02.21 um 23:00 schrieb Chris Wilson:
> 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.

This helps a lot with transactional programming in userspace system 
code. So FWIW

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

> 
> 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
> 
> ---
> 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)
>
Daniel Vetter Feb. 16, 2021, 9:02 a.m. UTC | #8
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@chris-wilson.co.uk>
> 
> Thanks!
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>

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@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
> > 
> > ---
> > 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
diff mbox series

Patch

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)