linux-kernel - Re: io_uring vs in_compat

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Message-ID: <ceb21006-26d0-b216-84a9-5da0b89b5fbf@kernel.dk>
Date:   Mon, 20 Jul 2020 10:36:40 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: io_uring vs in_compat_syscall()

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.

-- 
Jens Axboe