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Message-ID: <515DE24D.3080507@zytor.com>
Date: Thu, 04 Apr 2013 13:27:57 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Julien Tinnes <jln@...gle.com>
CC: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
x86@...nel.org, Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
Matthew Garrett <mjg@...hat.com>,
Matt Fleming <matt.fleming@...el.com>,
Eric Northup <digitaleric@...gle.com>,
Dan Rosenberg <drosenberg@...curity.com>,
Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR
On 04/04/2013 01:23 PM, Julien Tinnes wrote:
> On Thu, Apr 4, 2013 at 1:19 PM, Julien Tinnes <jln@...gle.com> wrote:
>> On Thu, Apr 4, 2013 at 1:12 PM, H. Peter Anvin <hpa@...or.com> 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 think privilege reduction in general, and sandboxing in particular,
>> can make KASLR even more useful. A lot of the information leaks can be
>> mitigated in the same way as attack surface and vulnerabilities can be
>> mitigated.
>
> Case in point:
> - leaks of 64 bits kernel values to userland in compatibility
> sub-mode. Sandboxing by using seccomp-bpf can restrict a process to
> the 64-bit mode API.
> - restricting access to the syslog() system call
>
That doesn't really speak to the value proposition. My concern is that
we're going to spend a lot of time chasing/plugging infoleaks instead of
tackling bigger problems.
8 bits of entropy is not a lot.
-hpa
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