From: Pavel Begunkov <[email protected]>
To: Andy Lutomirski <[email protected]>, Arnd Bergmann <[email protected]>
Cc: Andy Lutomirski <[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: Mon, 21 Sep 2020 19:13:18 +0300 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 21/09/2020 19:10, Pavel Begunkov wrote:
> On 20/09/2020 01:22, Andy Lutomirski wrote:
>>
>>> On Sep 19, 2020, at 2:16 PM, Arnd Bergmann <[email protected]> wrote:
>>>
>>> On Sat, Sep 19, 2020 at 6:21 PM Andy Lutomirski <[email protected]> wrote:
>>>>> On Fri, Sep 18, 2020 at 8:16 AM Christoph Hellwig <[email protected]> wrote:
>>>>> On Fri, Sep 18, 2020 at 02:58:22PM +0100, Al Viro wrote:
>>>>>> Said that, why not provide a variant that would take an explicit
>>>>>> "is it compat" argument and use it there? And have the normal
>>>>>> one pass in_compat_syscall() to that...
>>>>>
>>>>> That would help to not introduce a regression with this series yes.
>>>>> But it wouldn't fix existing bugs when io_uring is used to access
>>>>> read or write methods that use in_compat_syscall(). One example that
>>>>> I recently ran into is drivers/scsi/sg.c.
>>>
>>> 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.
--
Pavel Begunkov
next prev parent reply other threads:[~2020-09-21 16:15 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 [this message]
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
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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