* H. Peter Anvin [off-list ref] wrote:

On 06/20/2011 12:41 AM, Ingo Molnar wrote:

quoted

* H. Peter Anvin [off-list ref] wrote:

quoted

There are some test drivers which really want /dev/mem to work.

Test drivers and test hardware with zero enumeration can use below 4G 
addresses just fine.

Also, debugging is not an issue and some non-default kernel or boot 
option can enable any sort of device i guess, so my main worry isnt 
really security but that we should stand in the way of the apparent 
practice of *shipping* user-space drivers that use /dev/mem ...

We should either fix /dev/mem to work according to its 
specification or rip it out.  The issue with test drivers is not 
spurious... I ran into this one myself a few weeks ago while trying 
to do a memory test (by limiting the amount of memory available to 
the kernel).  This is something that is typically done on factory 
floors, and it would be nice to be able to get those environments 
over to using Linux.

There is no reason why they couldnt use a .config option or a boot 
option to get their weird stuff going, which weird stuff also happens 
to be useful.

What i'm somewhat against is having this enabled by default for weird 
stuff that also happens to be harmful - and the fact that it never 
worked over 4G physical gives us the perfect opportunity to do just 
that.

Thanks,

	Ingo