Messages in this thread | | | Date | Mon, 2 May 2016 19:21:28 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: GUP guarantees wrt to userspace mappings redesign |
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On Mon, May 02, 2016 at 04:15:38PM +0200, Oleg Nesterov wrote: > I am sure I missed the problem, but... > > On 05/02, Kirill A. Shutemov wrote: > > > > Quick look around: > > > > - 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.
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.
-- Kirill A. Shutemov
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