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Re: kern/45830: reading :dev/mem panics an i386 domU

The following reply was made to PR kern/45830; it has been noted by GNATS.

From: Wolfgang Solfrank <>
Subject: Re: kern/45830: reading :dev/mem panics an i386 domU
Date: Fri, 13 Jan 2012 14:09:33 +0100

 (Forwarding my reply to your question on tech-kern to place it
 into the PR:)
 No, this is not a bug, especially not, if this is run by root.
 /dev/mem is by definition the possibility to access the physical
 address space of the machine.  That is, apart from allowing access
 to the physical memory, it also allows access to memory mapped I/O
 etc.  Reading sequentially through this may or may not stumble upon
 one of these addresses before getting some error result (depending
 on the machine in question and the access rights).
 Access to /dev/mem requires specially crafted tools that know what
 they are doing.
 Regarding the mentioning of root in my first sentence, what I meant
 was that in (most of) our ports, there is code in the kernel that
 (depending on the secmodel in place) allows non-root users access
 only to real memory and returns an error otherwise (which happens to
 be wrong anyway, as it returns KAUTH_RESULT_* values as errno values,
 as I just found out when looking into this).
  From a security POV, access to /dev/mem should be restricted to
 root anyway (ok, based on the secmodel in place.  However, the
 current restriction of non-root access to memory only doesn't make
 too much sense; maybe a relict from some early frame buffer access?)
 --                                Wolfgang 

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