linux-kernel - Re: [RFC][PATCH] Cross Memory Attach

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Message-ID: <4CCFF1BA.1010206@redhat.com>
Date:	Tue, 02 Nov 2010 07:10:50 -0400
From:	Avi Kivity <avi@...hat.com>
To:	Christopher Yeoh <cyeoh@....ibm.com>
CC:	Bryan Donlan <bdonlan@...il.com>, linux-kernel@...r.kernel.org,
	Linux Memory Management List <linux-mm@...ck.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH] Cross Memory Attach

  On 11/01/2010 11:37 PM, Christopher Yeoh wrote:
> >
> >  You could have each process open /proc/self/mem and pass the fd using
> >  SCM_RIGHTS.
> >
> >  That eliminates a race; with copy_to_process(), by the time the pid
> >  is looked up it might designate a different process.
>
> Just to revive an old thread (I've been on holidays), but this doesn't
> work either. the ptrace check is done by mem_read (eg on each read) so
> even if you do pass the fd using SCM_RIGHTS, reads on the fd still
> fail.
>
> So unless there's good reason to believe that the ptrace permission
> check is no longer needed, the /proc/pid/mem interface doesn't seem to
> be an option for what we want to do.
>

Perhaps move the check to open().  I can understand the desire to avoid 
letting random processes peek each other's memory, but once a process 
has opened its own /proc/self/mem and explicitly passed it to another, 
we should allow it.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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