linux-kernel - Re: [PATCH 1/2] LSM: Do not apply mmap_min_addr check to PROT

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Message-Id: <20111024162842.CE1942C09C@topped-with-meat.com>
Date:	Mon, 24 Oct 2011 09:28:42 -0700 (PDT)
From:	Roland McGrath <roland@...k.frob.com>
To:	Eric Paris <eparis@...isplace.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morris <jmorris@...ei.org>,
	Stephen Smalley <sds@...ho.nsa.gov>, selinux@...ho.nsa.gov,
	John Johansen <john.johansen@...onical.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] LSM: Do not apply mmap_min_addr check to PROT_NONE
 mappings

> I feel like, and it's just a very vague feeling, that the PROT bits
> didn't matter to the kernel.  It would still happily execute stuff on
> page 0 even without PROT_EXEC at some point in the past.  I'm probably
> totally off base, and I could test it, but I sort of feel like I
> remember something like that....

Saying that PROT_EXEC might not be enforced is quite a different thing than
saying "PROT bits don't matter".  It's certainly the case that in some past
kernel versions, some hardware (older x86 chips), some configurations (x86
non-PAE), and some modes (READ_IMPLIES_EXEC personality stuff), what you
can read, you can execute.  I sincerely doubt it's ever been the case that
anything mapped as PROT_NONE could be accessed in any manner.


Thanks,
Roland
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