Re: [PATCH RFC v2 2/3] io_uring: add IOURING_REGISTER_RESTRICTIONS opcode

From: Stefano Garzarella <sgarzare@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Kees Cook <keescook@chromium.org>, Aleksa Sarai <asarai@suse.de>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Sargun Dhillon <sargun@sargun.me>, Jann Horn <jannh@google.com>,
	io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Jeff Moyer <jmoyer@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC v2 2/3] io_uring: add IOURING_REGISTER_RESTRICTIONS opcode
Date: Tue, 21 Jul 2020 12:40:09 +0200	[thread overview]
Message-ID: <20200721104009.lg626hmls5y6ihdr@steredhat> (raw)
In-Reply-To: <0fbb0393-c14f-3576-26b1-8bb22d2e0615@kernel.dk>

On Thu, Jul 16, 2020 at 03:26:51PM -0600, Jens Axboe wrote:
> On 7/16/20 6:48 AM, Stefano Garzarella wrote:
> > diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> > index efc50bd0af34..0774d5382c65 100644
> > --- a/include/uapi/linux/io_uring.h
> > +++ b/include/uapi/linux/io_uring.h
> > @@ -265,6 +265,7 @@ enum {
> >  	IORING_REGISTER_PROBE,
> >  	IORING_REGISTER_PERSONALITY,
> >  	IORING_UNREGISTER_PERSONALITY,
> > +	IORING_REGISTER_RESTRICTIONS,
> >  
> >  	/* this goes last */
> >  	IORING_REGISTER_LAST
> > @@ -293,4 +294,30 @@ struct io_uring_probe {
> >  	struct io_uring_probe_op ops[0];
> >  };
> >  
> > +struct io_uring_restriction {
> > +	__u16 opcode;
> > +	union {
> > +		__u8 register_op; /* IORING_RESTRICTION_REGISTER_OP */
> > +		__u8 sqe_op;      /* IORING_RESTRICTION_SQE_OP */
> > +	};
> > +	__u8 resv;
> > +	__u32 resv2[3];
> > +};
> > +
> > +/*
> > + * io_uring_restriction->opcode values
> > + */
> > +enum {
> > +	/* Allow an io_uring_register(2) opcode */
> > +	IORING_RESTRICTION_REGISTER_OP,
> > +
> > +	/* Allow an sqe opcode */
> > +	IORING_RESTRICTION_SQE_OP,
> > +
> > +	/* Only allow fixed files */
> > +	IORING_RESTRICTION_FIXED_FILES_ONLY,
> > +
> > +	IORING_RESTRICTION_LAST
> > +};
> > +
> 
> Not sure I totally love this API. Maybe it'd be cleaner to have separate
> ops for this, instead of muxing it like this. One for registering op
> code restrictions, and one for disallowing other parts (like fixed
> files, etc).
> 
> I think that would look a lot cleaner than the above.
> 

Talking with Stefan, an alternative, maybe more near to your suggestion,
would be to remove the 'struct io_uring_restriction' and add the
following register ops:

    /* Allow an sqe opcode */
    IORING_REGISTER_RESTRICTION_SQE_OP

    /* Allow an io_uring_register(2) opcode */
    IORING_REGISTER_RESTRICTION_REG_OP

    /* Register IORING_RESTRICTION_*  */
    IORING_REGISTER_RESTRICTION_OP

    enum {
        /* Only allow fixed files */
        IORING_RESTRICTION_FIXED_FILES_ONLY,

        IORING_RESTRICTION_LAST
    }

We can also enable restriction only when the rings started, to avoid to
register IORING_REGISTER_ENABLE_RINGS opcode. Once rings are started,
the restrictions cannot be changed or disabled.

If you agree, I'll send a v3 following this.

Thanks,
Stefano