Re: io_uring vs in_compat_syscall()

[Jens Axboe <axboe@kernel.dk>]

On 7/20/20 10:58 AM, Andy Lutomirski wrote:
> 
>> On Jul 20, 2020, at 9:37 AM, Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On 7/20/20 12:10 AM, Christoph Hellwig wrote:
>>> Hi Jens,
>>>
>>> I just found a (so far theoretical) issue with the io_uring submission
>>> offloading to workqueues or threads.  We have lots of places using
>>> in_compat_syscall() to check if a syscall needs compat treatmenet.
>>> While the biggest users is iocttl(), we also have a fair amount of
>>> places using in_compat_task() in read and write methods, and these
>>> will not do the wrong thing when used with io_uring under certain
>>> conditions.  I'm not sure how to best fix this, except for making sure
>>> in_compat_syscall() returns true one way or another for these cases.
>>
>> We can probably propagate this information in the io_kiocb via a flag,
>> and have the io-wq worker set TS_COMPAT if that's the case.
>>
> 
> Is TS_COMPAT actually a cross-arch concept for which this is safe?
> Having a real arch helper for “set the current syscall arch for the
> current kernel thread” seems more sensible to me. 

Sure, I'd consider that implementation detail for the actual patch(es)
for this issue.

-- 
Jens Axboe