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@xxxxxxxxxxxx> > --- > .../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
