linux-kernel - Re: mmap to address zero with MAP_FIXED returns ENOPERM for non-root users?

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Message-ID: <4CFB4386.3010806@brouhaha.com>
Date:	Sat, 04 Dec 2010 23:47:18 -0800
From:	Eric Smith <eric@...uhaha.com>
To:	Kyle Moffett <kyle@...fetthome.net>
CC:	linux-kernel@...r.kernel.org
Subject: Re: mmap to address zero with MAP_FIXED returns ENOPERM for non-root
 users?

Kyle Moffett wrote:
 > This is a specific security feature designed to reduce the security
 > impact of a kernel NULL-pointer dereference.

Thanks for the explanation!

 > Since you're performing binary translation of a microcontroller, it
 > may be better to perform some kind of minimal memory-map translation
 > as a part of that.

That's exactly what I'd hoped to avoid, as it does result in a 
non-trivial performance hit.  I suppose I can make it a configuration 
option of my translator.

I'm curious, though.  How likely are exploits where I can trick the 
kernel into calling a function at 0 in my virtual address space, but not 
trick it into calling a function at some non-zero address of my choosing?

Best regards,
Eric

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