Re: [PATCH 5/5] io_uring: add IORING_OP_WAITID support

["Arnd Bergmann" <arnd@arndb.de>]

On Fri, Jul 14, 2023, at 17:47, Christian Brauner wrote:
> On Tue, Jul 11, 2023 at 04:18:13PM -0600, Jens Axboe wrote:
>> On 7/11/23 3:22 PM, Jens Axboe wrote:
>> > On 7/11/23 3:11?PM, Arnd Bergmann wrote:

>> >> Does this require argument conversion for compat tasks?
>> >>
>> >> Even without the rusage argument, I think the siginfo
>> >> remains incompatible with 32-bit tasks, unfortunately.
>> > 
>> > Hmm yes good point, if compat_siginfo and siginfo are different, then it
>> > does need handling for that. Would be a trivial addition, I'll make that
>> > change. Thanks Arnd!
>> 
>> Should be fixed in the current version:
>> 
>> https://git.kernel.dk/cgit/linux/commit/?h=io_uring-waitid&id=08f3dc9b7cedbd20c0f215f25c9a7814c6c601cc
>
> In kernel/signal.c in pidfd_send_signal() we have
> copy_siginfo_from_user_any() it seems that a similar version
> copy_siginfo_to_user_any() might be something to consider. We do have
> copy_siginfo_to_user32() and copy_siginfo_to_user(). But I may lack
> context why this wouldn't work here.

We could add a copy_siginfo_to_user_any(), but I think open-coding
it is easier here, since the in_compat_syscall() check does not
work inside of the io_uring kernel thread, it has to be
"if (req->ctx->compat)" in order to match the wordsize of the task
that started the request.

Using copy_siginfo_to_user32() and copy_siginfo_to_user() is
probably a good idea though, it's often faster and less
error-prone than writing each member separately.

      Arnd