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

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Message-ID: <4c77d293-8eb9-01aa-27f8-7f320082e182@kernel.dk>
Date:   Mon, 25 Mar 2019 10:23:33 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>
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 3/25/19 10:19 AM, James Bottomley wrote:
> 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.

That requires the types to be valid for !CONFIG_COMPAT, as well as the
sigmask helper.

-- 
Jens Axboe