Re: [PATCHv2 1/3] uprobe: Add uretprobe syscall to speed up return probe

[Oleg Nesterov <oleg@redhat.com>]

On 04/08, Jiri Olsa wrote:
>
> On Fri, Apr 05, 2024 at 01:02:30PM +0200, Oleg Nesterov wrote:
> >
> > 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.

... or the task has uprobe at this address

> if not it treats that int3 as regular trap

Yes this mimics the "default" behaviour without uprobes/uretprobes

> 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

Agreed,

> 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

Agreed. In fact I think it should be also killed if copy_to/from_user()
fails by the same reason.

Oleg.