Re: [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension

[Gregory Price]

On Thu, Jan 26, 2023 at 10:53:49AM -0800, Andrei Vagin wrote:
> On Thu, Jan 26, 2023 at 10:30 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > On 01/26, Andrei Vagin wrote:
> > >
> > > On Thu, Jan 26, 2023 at 7:07 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > > >
> > > > IIUC, PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH is needed to run the injected
> > > > code, and this also needs to change the state of the traced process. If
> > > > the tracer (CRIU) dies while the tracee runs this code, I guess the tracee
> > > > will have other problems?
> > >
> > > Our injected code can reheal itself if something goes wrong. The hack
> > > here is that we inject
> > > the code with a signal frame and it calls rt_segreturn to resume the process.
> >
> > What will happen if CRIU dies and clears ->ptrace right before
> > syscall_user_dispatch() checks PT_SUSPEND_SYSCALL_USER_DISPATCH ?
> >
> > How the tracee will react to SIGSYS with unexpected .si_syscall ?
> 
> I got it. PTRACE_O_SUSPEND_SUD doesn't help us here, because we rely
> on sigreturn
> that is called after ptrace_detach. Thanks.
> 
> >
> > > I don't expect that
> > > the syscall user dispatch
> > > is used by many applications,
> >
> > Agreed, so the case when CRIU will need to do the additional
> > PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG twice to disable and then re-enable
> > syscall_user_dispatch is unlikely.
> >
> > > so I don't strongly insist on
> > > PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH.
> >
> > I too won't argue too much. but so far I do not feel there is enough
> > justification for this feature ...
> 
> Agree
> 
> >
> > Oleg.
> >

Seems that's consensus, I will drop it.