linux-kernel - Re: [PATCH 1/2] io_uring: fix big-endian compat signal mask handling

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Date:   Mon, 25 Mar 2019 09:19:26 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Hannes Reinecke <hare@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Nikolay Borisov <nborisov@...e.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] io_uring: fix big-endian compat signal mask handling

On Mon, 2019-03-25 at 15:34 +0100, Arnd Bergmann wrote:
> On big-endian architectures, the signal masks are differnet
> between 32-bit and 64-bit tasks, so we have to use a different
> function for reading them from user space.
> 
> io_cqring_wait() initially got this wrong, and always interprets
> this as a native structure. This is ok on x86 and most arm64,
> but not on s390, ppc64be, mips64be, sparc64 and parisc.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  fs/io_uring.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 6aaa30580a2b..8f48d29abf76 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1968,7 +1968,15 @@ static int io_cqring_wait(struct io_ring_ctx
> *ctx, int min_events,
>  		return 0;
>  
>  	if (sig) {
> -		ret = set_user_sigmask(sig, &ksigmask, &sigsaved,
> sigsz);
> +#ifdef CONFIG_COMPAT
> +		if (in_compat_syscall())
> +			ret = set_compat_user_sigmask((const
> compat_sigset_t __user *)sig,
> +						      &ksigmask,
> &sigsaved, sigsz);
> +		else
> +#endif

This looks a bit suboptimal: shouldn't in_compat_syscall() be hard
coded to return 0 if CONFIG_COMPAT isn't defined?  That way the
compiler can do the correct optimization and we don't have to litter
#ifdefs and worry about undefined variables and other things.

James