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Date: Fri, 12 Aug 2011 13:20:46 +0400
From: Solar Designer <solar@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Subject: Re: base address for shared libs
On Fri, Aug 12, 2011 at 12:20:24PM +0400, Vasiliy Kulikov wrote:
> However, some upstream guys don't agree it should be configurable:
>
> https://lkml.org/lkml/2006/5/19/219
>
> https://lkml.org/lkml/2006/5/22/207:
>
> "Because if it is configurable, someone _will_ configure it wrong, and
> then ask us why it does not work."
This is easily dealt with by limiting the allowable range to "correct"
values. Say, instead of 0 to 19 use 9 to 18 or 10 to 16. Then we'll
need to patch only the allowable range and not any code in Owl.
> Probably it worth trying to bring up the discussion of configurable ASLR
> entropy again - the code to configure it is simple anyway.
Yes, please - with a patch.
> However, I
> expect one nasty answer: "everybody should use x86-64 for good ASLR and
> other things, for x86-32 it is bad anyway, so don't bother to fix things
> broken by design."
You may simply reply that you disagree. Maybe someone else will as well.
> So, to summarize:
>
> For upstream we want to start mmap addresses allocation from 0x1100000,
You meant from 0x110000 (one zero less).
> bottom up.
Huh? I don't think you used the right words here.
> Probably, make entropy configurable.
Yes.
> For Owl we want to make entropy size configurable. Depending on the
> entropy, use ASCII-armor or fallback to the default allocator
> instantly.
Not exactly. Both for upstream and for Owl, when the entropy size
exceeds what we can provide ASCII-armor for, we start at 0x110000
anyway, but we just happen to go to non-armored addresses if we get such
random numbers. For example, if we're configured to use 12 bits and our
binary uses just one library of 3 MB in size, then there's an approx.
75% chance that on a given invocation of the binary we have ASCII armor
for the library anyway. This is just not guaranteed.
Alexander
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