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From: Pavel Begunkov <[email protected]>
To: Andy Lutomirski <[email protected]>
Cc: Arnd Bergmann <[email protected]>, Christoph Hellwig <[email protected]>,
	Al Viro <[email protected]>,
	Andrew Morton <[email protected]>,
	Jens Axboe <[email protected]>, David Howells <[email protected]>,
	linux-arm-kernel <[email protected]>,
	X86 ML <[email protected]>, LKML <[email protected]>,
	"open list:MIPS" <[email protected]>,
	Parisc List <[email protected]>,
	linuxppc-dev <[email protected]>,
	linux-s390 <[email protected]>,
	sparclinux <[email protected]>,
	linux-block <[email protected]>,
	Linux SCSI List <[email protected]>,
	Linux FS Devel <[email protected]>,
	linux-aio <[email protected]>,
	[email protected], linux-arch <[email protected]>,
	Linux-MM <[email protected]>,
	Network Development <[email protected]>,
	[email protected],
	LSM List <[email protected]>
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
Date: Tue, 22 Sep 2020 09:30:09 +0300	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CALCETrUEC81va8-fuUXG1uA5rbKxnKDYsDOXC70_HtKD4LAeAg@mail.gmail.com>

On 22/09/2020 03:58, Andy Lutomirski wrote:
> On Mon, Sep 21, 2020 at 5:24 PM Pavel Begunkov <[email protected]> wrote:
>>>>>>> Ah, so reading /dev/input/event* would suffer from the same issue,
>>>>>>> and that one would in fact be broken by your patch in the hypothetical
>>>>>>> case that someone tried to use io_uring to read /dev/input/event on x32...
>>>>>>>
>>>>>>> For reference, I checked the socket timestamp handling that has a
>>>>>>> number of corner cases with time32/time64 formats in compat mode,
>>>>>>> but none of those appear to be affected by the problem.
>>>>>>>
>>>>>>>> Aside from the potentially nasty use of per-task variables, one thing
>>>>>>>> I don't like about PF_FORCE_COMPAT is that it's one-way.  If we're
>>>>>>>> going to have a generic mechanism for this, shouldn't we allow a full
>>>>>>>> override of the syscall arch instead of just allowing forcing compat
>>>>>>>> so that a compat syscall can do a non-compat operation?
>>>>>>>
>>>>>>> The only reason it's needed here is that the caller is in a kernel
>>>>>>> thread rather than a system call. Are there any possible scenarios
>>>>>>> where one would actually need the opposite?
>>>>>>>
>>>>>>
>>>>>> I can certainly imagine needing to force x32 mode from a kernel thread.
>>>>>>
>>>>>> As for the other direction: what exactly are the desired bitness/arch semantics of io_uring?  Is the operation bitness chosen by the io_uring creation or by the io_uring_enter() bitness?
>>>>>
>>>>> It's rather the second one. Even though AFAIR it wasn't discussed
>>>>> specifically, that how it works now (_partially_).
>>>>
>>>> Double checked -- I'm wrong, that's the former one. Most of it is based
>>>> on a flag that was set an creation.
>>>>
>>>
>>> Could we get away with making io_uring_enter() return -EINVAL (or
>>> maybe -ENOTTY?) if you try to do it with bitness that doesn't match
>>> the io_uring?  And disable SQPOLL in compat mode?
>>
>> Something like below. If PF_FORCE_COMPAT or any other solution
>> doesn't lend by the time, I'll take a look whether other io_uring's
>> syscalls need similar checks, etc.
>>
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 0458f02d4ca8..aab20785fa9a 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -8671,6 +8671,10 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
>>         if (ctx->flags & IORING_SETUP_R_DISABLED)
>>                 goto out;
>>
>> +       ret = -EINVAl;
>> +       if (ctx->compat != in_compat_syscall())
>> +               goto out;
>> +
> 
> This seems entirely reasonable to me.  Sharing an io_uring ring
> between programs with different ABIs seems a bit nutty.
> 
>>         /*
>>          * For SQ polling, the thread will do all submissions and completions.
>>          * Just return the requested submit count, and wake the thread if
>> @@ -9006,6 +9010,10 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
>>         if (ret)
>>                 goto err;
>>
>> +       ret = -EINVAL;
>> +       if (ctx->compat)
>> +               goto err;
>> +
> 
> I may be looking at a different kernel than you, but aren't you
> preventing creating an io_uring regardless of whether SQPOLL is
> requested?

I diffed a not-saved file on a sleepy head, thanks for noticing.
As you said, there should be an SQPOLL check.

...
if (ctx->compat && (p->flags & IORING_SETUP_SQPOLL))
	goto err;

-- 
Pavel Begunkov

  reply	other threads:[~2020-09-22  6:32 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 12:45 let import_iovec deal with compat_iovecs as well Christoph Hellwig
2020-09-18 12:45 ` [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag Christoph Hellwig
2020-09-18 13:40   ` Al Viro
2020-09-18 13:44     ` Christoph Hellwig
2020-09-18 13:58       ` Al Viro
2020-09-18 15:16         ` Christoph Hellwig
2020-09-19 16:21           ` Andy Lutomirski
2020-09-19 21:16             ` Arnd Bergmann
2020-09-19 21:52               ` Finn Thain
2020-09-19 22:22               ` Andy Lutomirski
2020-09-21 16:10                 ` Pavel Begunkov
2020-09-21 16:13                   ` Pavel Begunkov
2020-09-21 23:51                     ` Andy Lutomirski
2020-09-22  0:22                       ` Pavel Begunkov
2020-09-22  0:58                         ` Andy Lutomirski
2020-09-22  6:30                           ` Pavel Begunkov [this message]
2020-09-22  7:23                             ` Arnd Bergmann
2020-09-22  7:57                               ` Pavel Begunkov
2020-09-22  9:01                                 ` Arnd Bergmann
2020-09-22 16:20                                   ` Andy Lutomirski
2020-09-23  8:01                                   ` Pavel Begunkov
2020-09-23 13:22                                     ` Al Viro
2020-09-19 22:09           ` Al Viro
2020-09-19 22:23             ` Andy Lutomirski
2020-09-19 22:41               ` Al Viro
2020-09-19 22:53                 ` Andy Lutomirski
2020-09-19 23:24                   ` Al Viro
2020-09-20  0:14                     ` Andy Lutomirski
2020-09-20  2:57                       ` Al Viro
2020-09-20 16:59                         ` Andy Lutomirski
2020-09-20 18:12                           ` Al Viro
2020-09-20 13:55             ` Arnd Bergmann
2020-09-20 15:02               ` Al Viro
2020-09-19 14:53         ` David Laight
2020-09-18 13:59       ` Arnd Bergmann
2020-09-20 15:15   ` Matthew Wilcox
2020-09-20 15:55     ` William Kucharski
2020-09-21 16:20       ` Pavel Begunkov
2020-09-20 16:00     ` Arnd Bergmann
2020-09-20 18:07     ` Al Viro
2020-09-20 18:41       ` Al Viro
2020-09-20 19:01       ` Matthew Wilcox
2020-09-20 19:10         ` Al Viro
2020-09-20 19:22           ` Matthew Wilcox
2020-09-20 19:28             ` Andy Lutomirski
2020-09-20 20:49               ` Arnd Bergmann
2020-09-20 21:13                 ` David Laight
2020-09-21 16:31                   ` Pavel Begunkov
2020-09-20 21:42             ` Al Viro
2020-09-21 16:26             ` Pavel Begunkov
2020-09-20 19:14       ` Andy Lutomirski
2020-09-21  4:28         ` Christoph Hellwig
2020-09-18 12:45 ` [PATCH 2/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-18 13:37   ` Johannes Thumshirn
2020-09-18 12:45 ` [PATCH 3/9] fs: explicitly check for CHECK_IOVEC_ONLY in rw_copy_check_uvector Christoph Hellwig
2020-09-18 12:56   ` Matthew Wilcox
2020-09-18 13:39   ` Johannes Thumshirn
2020-09-18 12:45 ` [PATCH 4/9] fs: handle the compat case in import_iovec Christoph Hellwig
2020-09-18 12:45 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-18 12:45 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-18 12:45 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-18 12:45 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-18 13:48   ` Arnd Bergmann
2020-09-18 12:45 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
2020-09-19 14:24 ` let import_iovec deal with compat_iovecs as well David Laight
2020-09-21  4:41   ` 'Christoph Hellwig'
2020-09-21 11:11     ` David Laight

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