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From: Pavel Begunkov <asml.silence@gmail.com>
To: David Laight <David.Laight@ACULAB.COM>,
	'Arnd Bergmann' <arnd@arndb.de>,
	Andy Lutomirski <luto@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, David Howells <dhowells@redhat.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
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	"open list:MIPS" <linux-mips@vger.kernel.org>,
	Parisc List <linux-parisc@vger.kernel.org>,
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	linux-arch <linux-arch@vger.kernel.org>,
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	LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
Date: Mon, 21 Sep 2020 19:31:49 +0300
Message-ID: <7fc71d22-e213-b050-75fe-b45adc6bf0d8@gmail.com> (raw)
In-Reply-To: <8363d874e503470f8caa201e85e9fbd4@AcuMS.aculab.com>

On 21/09/2020 00:13, David Laight wrote:
> From: Arnd Bergmann
>> Sent: 20 September 2020 21:49
>>
>> On Sun, Sep 20, 2020 at 9:28 PM Andy Lutomirski <luto@kernel.org> wrote:
>>> On Sun, Sep 20, 2020 at 12:23 PM Matthew Wilcox <willy@infradead.org> wrote:
>>>>
>>>> On Sun, Sep 20, 2020 at 08:10:31PM +0100, Al Viro wrote:
>>>>> IMO it's much saner to mark those and refuse to touch them from io_uring...
>>>>
>>>> Simpler solution is to remove io_uring from the 32-bit syscall list.
>>>> If you're a 32-bit process, you don't get to use io_uring.  Would
>>>> any real users actually care about that?
>>>
>>> We could go one step farther and declare that we're done adding *any*
>>> new compat syscalls :)
>>
>> Would you also stop adding system calls to native 32-bit systems then?
>>
>> On memory constrained systems (less than 2GB a.t.m.), there is still a
>> strong demand for running 32-bit user space, but all of the recent Arm
>> cores (after Cortex-A55) dropped the ability to run 32-bit kernels, so
>> that compat mode may eventually become the primary way to run
>> Linux on cheap embedded systems.
>>
>> I don't think there is any chance we can realistically take away io_uring
>> from the 32-bit ABI any more now.
> 
> Can't it just run requests from 32bit apps in a kernel thread that has
> the 'in_compat_syscall' flag set?
> Not that i recall seeing the code where it saves the 'compat' nature
> of any requests.
> 
> It is already completely f*cked if you try to pass the command ring
> to a child process - it uses the wrong 'mm'.

And how so? io_uring uses mm of a submitter. The exception is SQPOLL
mode, but it requires CAP_SYS_ADMIN or CAP_SYS_NICE anyway.

> I suspect there are some really horrid security holes in that area.
> 
> 	David.
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

-- 
Pavel Begunkov

  reply index

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 [this message]
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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