On Mon, Jan 09, 2023 at 10:33:48AM -0500, Gregory Price wrote:
This patch implements simple getter interface for syscall user dispatch configuration info.
To support checkpoint/resume of a syscall user dispatch process, the prctl settings for syscall user dispatch must be fetchable. Presently, these settings are write-only, making it impossible to implement transparent checkpoint (coordination with the software is required).
As Syscall User Dispatch is explicitly not for secure-container development, exposing the configuration state via prctl does not violate the original design intent.
Signed-off-by: Gregory Price gregory.price@memverge.com
.../admin-guide/syscall-user-dispatch.rst | 18 +++++++ include/linux/syscall_user_dispatch.h | 7 +++ include/uapi/linux/prctl.h | 3 ++ kernel/entry/syscall_user_dispatch.c | 14 +++++ kernel/sys.c | 4 ++ .../syscall_user_dispatch/sud_test.c | 54 +++++++++++++++++++ 6 files changed, 100 insertions(+)
diff --git a/Documentation/admin-guide/syscall-user-dispatch.rst b/Documentation/admin-guide/syscall-user-dispatch.rst index 60314953c728..8b2c8b6441b7 100644 --- a/Documentation/admin-guide/syscall-user-dispatch.rst +++ b/Documentation/admin-guide/syscall-user-dispatch.rst @@ -45,6 +45,10 @@ only the syscall dispatcher address and the userspace key. As the ABI of these intercepted syscalls is unknown to Linux, these syscalls are not instrumentable via ptrace or the syscall tracepoints. +A getter interface is supplied for the purpose of userland +checkpoint/restore software being able to suspend and restore the +current state of the system.
Interface
@@ -73,6 +77,20 @@ thread-wide, without the need to invoke the kernel directly. selector can be set to SYSCALL_DISPATCH_FILTER_ALLOW or SYSCALL_DISPATCH_FILTER_BLOCK. Any other value should terminate the program with a SIGSYS.
+A thread can fetch the current Syscall User Dispatch configuration with the following prctl:
- prctl(PR_GET_SYSCALL_USER_DISPATCH, <dispatch_config>))
+<dispatch_config> is a pointer to a ``struct syscall_user_dispatch`` as defined in ``linux/include/linux/syscall_user_dispatch.h``::
syscall_user_dispatch.h isn't a part of uapi, so I am not sure that it is a good idea to use it here.
For criu, it is much more convinient to have a ptrace interface to get this sort of parameters. prctl requires to execute a system call from a context of the target process. It is tricky so we want to minimize a number of such calls.
Thanks, Andrei