mmap_min_addr info

[swair shah]

quoting the debian wiki for mmap_min_add. "Allowing processes to map low
values increases the security implications of a class of defects known as
"kernel NULL pointer dereference" defects... The downside to preventing
applications from mmap'ing low virtual memory addresses is that certain
applications depend on this functionality. dosemu, qemu and wine are three
such applications that exist in Debian"

I don't understand the use of the mmap_min_add. What's the point of
preventing applications from mapping to low memory values. Also why would
applications mentioned here would need to map to low memory addresses? A
little descriptive explanation would be very helpful!
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