On Tue, Apr 09, 2024 at 09:34:39AM +0900, Masami Hiramatsu wrote:
SNIP
> > >
> > > > this can be fixed by checking the syscall is called from the trampoline
> > > > and prevent handle_trampoline call if it's not
> > >
> > > Yes, but I still do not think this makes a lot of sense. But I won't argue.
> > >
> > > And what should sys_uretprobe() do if it is not called from the trampoline?
> > > I'd prefer force_sig(SIGILL) to punish the abuser ;) OK, OK, EINVAL.
> >
> > so the similar behaviour with int3 ends up with immediate SIGTRAP
> > and not invoking pending uretprobe consumers, like:
> >
> > - setup uretprobe for foo
> > - foo() {
> > executes int 3 -> sends SIGTRAP
> > }
> >
> > because the int3 handler checks if it got executed from the uretprobe's
> > trampoline.. if not it treats that int3 as regular trap
>
> Yeah, that is consistent behavior. Sounds good to me.
>
> >
> > while for uretprobe syscall we have at the moment following behaviour:
> >
> > - setup uretprobe for foo
> > - foo() {
> > uretprobe_syscall -> executes foo's uretprobe consumers
> > }
> > - at some point we get to the 'ret' instruction that jump into uretprobe
> > trampoline and the uretprobe_syscall won't find pending uretprobe and
> > will send SIGILL
> >
> >
> > so I think we should mimic int3 behaviour and:
> >
> > - setup uretprobe for foo
> > - foo() {
> > uretprobe_syscall -> check if we got executed from uretprobe's
> > trampoline and send SIGILL if that's not the case
>
> OK, this looks good to me.
>
> >
> > I think it's better to have the offending process killed right away,
> > rather than having more undefined behaviour, waiting for final 'ret'
> > instruction that jumps to uretprobe trampoline and causes SIGILL
> >
> > >
> > > I agree very much with Andrii,
> > >
> > > sigreturn() exists only to allow the implementation of signal handlers. It should never be
> > > called directly. Details of the arguments (if any) passed to sigreturn() vary depending on
> > > the architecture.
> > >
> > > this is how sys_uretprobe() should be treated/documented.
> >
> > yes, will include man page patch in new version
>
> And please follow Documentation/process/adding-syscalls.rst in new version,
> then we can avoid repeating the same discussion :-)
yep, will do
thanks,
jirka
