Re: anonymous mmap() and random heap allocation

[Mikael Pettersson]

Xianghua Xiao writes:
 > It seems mmap() can not do random allocation for malloc()/heap on
 > Linux, anyone used pax's 'mmap randonness' option for that? what's the
 > price for that?
 > 
 > I want to port openbsd's malloc() to linux to avoid heap
 > crashes(overrun/underrun), openbsd's malloc() can do random allocation
 > for security reasons, meanwhile it helps to avoid some
 > overrun/underrun crashes with no extra cost, the latter is what I'm
 > looking for.

You can implement this in user-space with existing kernel features.
1: place guard pages around mmap():ed data
2: parse /proc/self/maps and mmap(MAP_FIXED)
3: use a "safe" compiler or a dynamic binary instrumenter
4: use x86 segments (ugh!)
5: use a safe programming language
...
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