linux-kernel - Re: [PATCH] mmap: add sysctl for controlling ~VM

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Date:	Tue, 16 Aug 2011 12:46:17 -0700
From:	Roland McGrath <mcgrathr@...gle.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Nitin Gupta <ngupta@...are.org>,
	Hugh Dickins <hughd@...gle.com>,
	Shaohua Li <shaohua.li@...el.com>, linux-mm@...ck.org
Subject: Re: [PATCH] mmap: add sysctl for controlling ~VM_MAYEXEC taint

On Tue, Aug 16, 2011 at 12:40 PM, Mel Gorman <mel@....ul.ie> wrote:
> They might result in the same system call but one of them creates
> the file under /dev/shm which should not have the same permissions
> problem. The library really appears to want to create a shared
> executable object, using shm_open does not appear that unreasonable
> to me.

People do use shm_open.  Some systems mount /dev/shm with noexec.
That's why we're here in the first place.

> Which then needs to be copied in each distro wanting to do the same
> thing and is not backwards compatible where as using shm_open is.

Each distro wanting to set noexec on its /dev/shm mounts has to set the
sysctl (or its default in their kernel builds), yes.  Otherwise they are
not compatible with the expectation of using PROT_EXEC on files opened with
shm_open.


Thanks,
Roland
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