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From: Andy Lutomirski <[email protected]>
To: Al Viro <[email protected]>
Cc: Matthew Wilcox <[email protected]>,
	Christoph Hellwig <[email protected]>,
	Andrew Morton <[email protected]>,
	Jens Axboe <[email protected]>, Arnd Bergmann <[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: Sun, 20 Sep 2020 12:14:49 -0700	[thread overview]
Message-ID: <CALCETrWHW4wHG+Z-mxsY-kvjSi+S6gRUQ+LHd9syPcm5bhi3cw@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>

On Sun, Sep 20, 2020 at 11:07 AM Al Viro <[email protected]> wrote:
>
> On Sun, Sep 20, 2020 at 04:15:10PM +0100, Matthew Wilcox wrote:
> > On Fri, Sep 18, 2020 at 02:45:25PM +0200, Christoph Hellwig wrote:
> > > Add a flag to force processing a syscall as a compat syscall.  This is
> > > required so that in_compat_syscall() works for I/O submitted by io_uring
> > > helper threads on behalf of compat syscalls.
> >
> > Al doesn't like this much, but my suggestion is to introduce two new
> > opcodes -- IORING_OP_READV32 and IORING_OP_WRITEV32.  The compat code
> > can translate IORING_OP_READV to IORING_OP_READV32 and then the core
> > code can know what that user pointer is pointing to.
>
> Let's separate two issues:
>         1) compat syscalls want 32bit iovecs.  Nothing to do with the
> drivers, dealt with just fine.
>         2) a few drivers are really fucked in head.  They use different
> *DATA* layouts for reads/writes, depending upon the calling process.
> IOW, if you fork/exec a 32bit binary and your stdin is one of those,
> reads from stdin in parent and child will yield different data layouts.
> On the same struct file.
>         That's what Christoph worries about (/dev/sg he'd mentioned is
> one of those).
>
>         IMO we should simply have that dozen or so of pathological files
> marked with FMODE_SHITTY_ABI; it's not about how they'd been opened -
> it describes the userland ABI provided by those.  And it's cast in stone.
>

I wonder if this is really quite cast in stone.  We could also have
FMODE_SHITTY_COMPAT and set that when a file like this is *opened* in
compat mode.  Then that particular struct file would be read and
written using the compat data format.  The change would be
user-visible, but the user that would see it would be very strange
indeed.

I don't have a strong opinion as to whether that is better or worse
than denying io_uring access to these things, but at least it moves
the special case out of io_uring.

--Andy

  parent reply	other threads:[~2020-09-20 19:15 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
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 [this message]
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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