Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: io_uring vs in_compat_syscall()
To:     Christoph Hellwig <hch@lst.de>
Cc:     linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org, io-uring@vger.kernel.org
References: <20200720061046.GA10678@lst.de>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <ceb21006-26d0-b216-84a9-5da0b89b5fbf@kernel.dk>
Date:   Mon, 20 Jul 2020 10:36:40 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20200720061046.GA10678@lst.de>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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