linux-kernel - Re: [patch] remove MNT_NOEXEC check for PROT

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Date:	Sun, 24 Sep 2006 19:14:02 +0000 (UTC)
From:	daw@...berkeley.edu (David Wagner)
To:	linux-kernel@...r.kernel.org
Subject: Re: [patch] remove MNT_NOEXEC check for PROT_EXEC mmaps

Stas Sergeev  wrote:
>Ulrich Drepper wrote:
>> The consensus has been to add the same checks to mprotect.  They were
>> not left out intentionally.
>
>But how about the anonymous mmap with PROT_EXEC set?

I'm curious about this, too.  ld-linux.so is a purely unprivileged
program.  It isn't setuid root.  Can you write a variant of ld-linux.so
that reads an executable into memory off of a partition mounted noexec and
then begins executing that code?  (perhaps by using anonymous mmap with
PROT_EXEC or some other mechanism) It sure seems like the answer would
be yes.  If so, I'm having a hard time understanding what guarantees
noexec gives you.  Isn't the noexec flag just a speedbump that raises
the bar a little but doesn't really prevent anything?
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