linux-kernel - Re: [PATCH 6/7] mm: kill vma flag VM

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Message-ID: <20120405205304.GL8718@moon>
Date:	Fri, 6 Apr 2012 00:53:04 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	"oprofile-list@...ts.sf.net" <oprofile-list@...ts.sf.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE

On Thu, Apr 05, 2012 at 01:29:04PM -0700, Matt Helsley wrote:
...
> > > Doesn't that break the semantics of the kernel ABI?
> > 
> > Which one? exe_file can be changed iif there is no MAP_EXECUTABLE left.
> > Still, once assigned (via this prctl) the mm_struct::exe_file can't be changed
> > again, until program exit.
> 
> The prctl() interface itself is fine as it stands now.
> 
> As far as I can tell Konstantin is proposing that we remove the unusual
> counter that tracks the number of mappings of the exe_file and require
> userspace use the prctl() to drop the last reference. That's what I think
> will break the ABI because after that change you *must* change userspace
> code to use the prctl(). It's an ABI change because the same sequence of
> system calls with the same input bits produces different behavior.

Hi Matt, I see what you mean (I misread your email at first, sorry).
Sure it's impossible to patch already existing programs (and btw, this
prctl code actually won't help a program to drop symlink completely
and live without it then, because old one will gone but new one
will be assigned) so personally I can't answer here on Konstantin's
behalf, but I guess the main question is -- which programs use this
'drop-all-MAP_EXECUTABLE' feature?

	Cyrill
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