Re: [PATCH] 2.6.16.16 Parameter-controlled mmap/stack randomization

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

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Oh, some of my stuff is 4096 hard-coded instead of PAGE_SIZE.  I fixed
this in mmap() randomization here, but there's iffiness coming up for
the stack.

The stack is page aligned and randomized in the VMA; then randomized to
16 byte intervals.  This is fine, PAGE_SIZE is 4096, our intervals are
16, 256 positions, we randomize 2^(stack_random_bits - 8) VMA and 2^8
inside; unless we have less than 8 bits, then we randomize
2^stack_random_bits and align to PAGE_SIZE / (2^stack_random_bits).

Easy enough.  Now what if PAGE_SIZE isn't 4096?

That's an easy problem too.  This can easily be calculated straight
forward with the number ... 8.  In fact that's how I did it.  2^8 is
4096 / 16.  Thus, the solution is log_base_2(PAGE_SIZE/16) instead of 8!

Now.  How do I find the base 2 log of a number in the kernel?

John Richard Moser wrote:
> Any comments on this one?
> 
> I'm trying to control the stack and heap randomization via command-line
> parameters.  I wrote this in a 2.6.15 Ubuntu Dapper kernel and then
> patched it into a 2.6.16.16 tree and cleaned it up.  It does a few
> simple things:
> 

[SNIP]

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