Home
Reading
Searching
Subscribe
Sponsors
Statistics
Posting
Contact
Spam
Lists
Links
About
Hosting
Filtering
Features Download
Marketing
Archives
FAQ
Blog
 
Gmane
From: H. Peter Anvin <hpa <at> zytor.com>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR
Newsgroups: gmane.linux.kernel.hardened.devel
Date: Thursday 4th April 2013 20:58:06 UTC (over 4 years ago)
It seems to me that you are assuming that the attacker is targeting a
specific system, but a bot might as well target 256 different systems and
see what sticks...

Kees Cook  wrote:

>On Thu, Apr 4, 2013 at 1:12 PM, H. Peter Anvin  wrote:
>> On 04/04/2013 01:07 PM, Kees Cook wrote:
>>> However, the benefits of
>>> this feature in certain environments exceed the perceived
>weaknesses[2].
>>
>> Could you clarify?
>
>I would summarize the discussion of KASLR weaknesses into to two
>general observations:
>1- it depends on address location secrecy and leaks are common/easy.
>2- it has low entropy so attack success rates may be high.
>
>For "1", as Julien mentions, remote attacks and attacks from a
>significantly contained process (via seccomp-bpf) minimizes the leak
>exposure. For local attacks, cache timing attacks and other things
>also exist, but the ASLR can be improved to defend against that too.
>So, KASLR is useful on systems that are virtualization hosts,
>providing remote services, or running locally confined processes.
>
>For "2", I think that the comparison to userspace ASLR entropy isn't
>as direct. For userspace, most systems don't tend to have any kind of
>watchdog on segfaulting processes, so a remote attacker could just
>keep trying an attack until they got lucky, in which case low entropy
>is a serious problem. In the case of KASLR, a single attack failure
>means the system goes down, which makes mounting an attack much more
>difficult. I think 8 bits is fine to start with, and I think start
>with a base offset ASLR is a good first step. We can improve things in
>the future.
>
>-Kees
>
>--
>Kees Cook
>Chrome OS Security

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
 
CD: 3ms