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Message-ID: <1553530766.2955.51.camel@HansenPartnership.com>
Subject: Re: [PATCH 1/2] io_uring: fix big-endian compat signal mask handling
From:   James Bottomley <James.Bottomley@HansenPartnership.com>
To:     Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Hannes Reinecke <hare@suse.com>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Nikolay Borisov <nborisov@suse.com>,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Mon, 25 Mar 2019 09:19:26 -0700
In-Reply-To: <20190325143521.34928-1-arnd@arndb.de>
References: <20190325143521.34928-1-arnd@arndb.de>
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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@arndb.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