linux-kernel - Re: [PATCH v4 1/3] io_uring: use an enumeration for io_uring

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Message-ID: <202008261241.074D8765@keescook>
Date:   Wed, 26 Aug 2020 12:43:07 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jann Horn <jannh@...gle.com>, Jeff Moyer <jmoyer@...hat.com>,
        linux-fsdevel@...r.kernel.org, Sargun Dhillon <sargun@...gun.me>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        linux-kernel@...r.kernel.org, Aleksa Sarai <asarai@...e.de>,
        io-uring@...r.kernel.org
Subject: Re: [PATCH v4 1/3] io_uring: use an enumeration for
 io_uring_register(2) opcodes

On Thu, Aug 13, 2020 at 05:32:52PM +0200, Stefano Garzarella wrote:
> The enumeration allows us to keep track of the last
> io_uring_register(2) opcode available.
> 
> Behaviour and opcodes names don't change.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>  include/uapi/linux/io_uring.h | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index d65fde732518..cdc98afbacc3 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -255,17 +255,22 @@ struct io_uring_params {
>  /*
>   * io_uring_register(2) opcodes and arguments
>   */
> -#define IORING_REGISTER_BUFFERS		0
> -#define IORING_UNREGISTER_BUFFERS	1
> -#define IORING_REGISTER_FILES		2
> -#define IORING_UNREGISTER_FILES		3
> -#define IORING_REGISTER_EVENTFD		4
> -#define IORING_UNREGISTER_EVENTFD	5
> -#define IORING_REGISTER_FILES_UPDATE	6
> -#define IORING_REGISTER_EVENTFD_ASYNC	7
> -#define IORING_REGISTER_PROBE		8
> -#define IORING_REGISTER_PERSONALITY	9
> -#define IORING_UNREGISTER_PERSONALITY	10
> +enum {
> +	IORING_REGISTER_BUFFERS,

Actually, one *tiny* thought. Since this is UAPI, do we want to be extra
careful here and explicitly assign values? We can't change the meaning
of a number (UAPI) but we can add new ones, etc? This would help if an
OP were removed (to stop from triggering a cascade of changed values)...

for example:

enum {
	IORING_REGISTER_BUFFERS = 0,
	IORING_UNREGISTER_BUFFERS = 1,
	...


-- 
Kees Cook