Re: Patch 4/6 randomize the stack pointer

[John Richard Moser <nigelenki@comcast.net>]

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Linus Torvalds wrote:
> 

[...]

> 
> Your suggestion of 256MB of randomization for the stack SIMPLY IS NOT 
> ACCEPTABLE for a lot of uses. People on 32-bit archtiectures have issues 
> with usable virtual memory areas etc.
> 

I feel the need to point something out here.

[TEXT][BRK][MMAP---------------][STACK]

Here's a normal layout.

[TEXT][BRK][MMAP-------][STACK][MMAP--]

Is this one any worse?  Just bias non-executable mappings above the
stack when, say, half of VMA is used up.  Prevent executable mappings
from being created up there because PaX' PAGEEXEC and Exec Shield's
emulation will be affected by a high-mapping (PaX falls back to
kernel-assisted MMU walking, which can be very high overhead; ES just
makes everything below the area executable).

So, you can do it without losing VMA, in theory.


[...]

> 

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