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From: Oleg Nesterov <oleg@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Jerome Glisse <j.glisse@gmail.com>,
	Hugh Dickins <hughd@google.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
	"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: GUP guarantees wrt to userspace mappings redesign
Date: Mon, 2 May 2016 18:22:11 +0200	[thread overview]
Message-ID: <20160502162211.GA11678@redhat.com> (raw)
In-Reply-To: <20160502162128.GF24419@node.shutemov.name>

On 05/02, Kirill A. Shutemov wrote:
>
> On Mon, May 02, 2016 at 04:15:38PM +0200, Oleg Nesterov wrote:
> > >
> > >  - I don't see any check page_count() around __replace_page() in uprobes,
> > >    so it can easily replace pinned page.
> >
> > Why it should? even if it races with get_user_pages_fast()... this doesn't
> > differ from the case when an application writes to MAP_PRIVATE non-anonymous
> > region, no?
>
> < I know nothing about uprobes or ptrace in general >
>
> I think the difference is that the write is initiated by the process
> itself, but IIUC __replace_page() can be initiated by other process, so
> it's out of control of the application.

Yes. Just like gdb can insert a breakpoint into the read-only executable vma.

> So we have pages pinned by a driver and the driver expects the pinned
> pages to be mapped into userspace, then __replace_page() kicks in and put
> different page there -- driver's expectation is broken.

Yes... but I don't understand the problem space. I mean, I do not know why
this driver should expect this, how it can be broken, etc.

I do not even understand why "initiated by other process" can make any
difference... Unless this driver somehow controls all threads which could
have this page mapped.

Oleg.

  reply	other threads:[~2016-05-02 17:24 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-28 16:20 [BUG] vfio device assignment regression with THP ref counting redesign Alex Williamson
2016-04-28 18:17 ` Kirill A. Shutemov
2016-04-28 18:58   ` Alex Williamson
2016-04-28 23:21     ` Andrea Arcangeli
2016-04-29  0:44       ` Alex Williamson
2016-04-29  0:51       ` Kirill A. Shutemov
2016-04-29  2:45         ` Alex Williamson
2016-04-29  7:06           ` Kirill A. Shutemov
2016-04-29 15:12             ` Alex Williamson
2016-04-29 16:34             ` Andrea Arcangeli
2016-04-29 22:34               ` Alex Williamson
2016-05-02 10:41               ` Kirill A. Shutemov
2016-05-02 11:15                 ` Jerome Glisse
2016-05-02 12:14                   ` GUP guarantees wrt to userspace mappings redesign Kirill A. Shutemov
2016-05-02 13:39                     ` Jerome Glisse
2016-05-02 15:00                       ` GUP guarantees wrt to userspace mappings Kirill A. Shutemov
2016-05-02 15:22                         ` Jerome Glisse
2016-05-02 16:12                           ` Kirill A. Shutemov
2016-05-02 19:14                             ` Andrea Arcangeli
2016-05-02 19:11                           ` Andrea Arcangeli
2016-05-02 19:02                         ` Andrea Arcangeli
2016-05-02 14:15                     ` GUP guarantees wrt to userspace mappings redesign Oleg Nesterov
2016-05-02 16:21                       ` Kirill A. Shutemov
2016-05-02 16:22                         ` Oleg Nesterov [this message]
2016-05-02 18:03                           ` Kirill A. Shutemov
2016-05-02 17:41                             ` Oleg Nesterov
2016-05-02 18:56                     ` Andrea Arcangeli
2016-05-02 15:23                 ` [BUG] vfio device assignment regression with THP ref counting redesign Andrea Arcangeli
2016-05-02 16:00                   ` Kirill A. Shutemov
2016-05-02 18:03                     ` Andrea Arcangeli
2016-05-05  1:19                       ` Alex Williamson
2016-05-05 14:39                         ` Andrea Arcangeli
2016-05-05 15:09                           ` Andrea Arcangeli
2016-05-05 15:11                           ` Kirill A. Shutemov
2016-05-05 15:24                             ` Andrea Arcangeli
2016-05-06  7:29                               ` Kirill A. Shutemov

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