linux-kernel - Re: [PATCH v6 0/7] Kernel base address randomization

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Message-ID: <fcdac020-6b9a-4d36-b424-290597669cb0@email.android.com>
Date:	Tue, 01 Oct 2013 22:11:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org,
	kernel-hardening@...ts.openwall.com, adurbin@...gle.com,
	Eric Northup <digitaleric@...gle.com>, jln@...gle.com,
	wad@...gle.com, Mathias Krause <minipli@...glemail.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 0/7] Kernel base address randomization

I think that the randomization offset would be necessary in order to identify pointers.

Ingo Molnar <mingo@...nel.org> wrote:
>
>* Kees Cook <keescook@...omium.org> wrote:
>
>> Here is the latest version of the kASLR series. It has much improved 
>> e820 walking code, and expands the window available on 64-bit.
>> 
>> This is rolled out on Chrome OS devices, and working well.
>
>There's one kernel debuggability detail that should be discussed I
>think: 
>should symbolic printouts (in oops messages but also in /proc/kallsyms)
>
>and instrumentation interfaces that expose kernel addresses attempt to 
>de-randomize the addresses, stack contents and register values that lie
>
>within the random range?
>
>- it would be easier to use those addresses and look them up in a
>vmlinux
>   or in a System.map as well.
>
> - it would be somewhat safer to post an oops publicly if it did not
>   contain the random offset in an easily identifiable way.
>
>- oops patterns from distribution kernels that enable randomization
>would 
>   match up better.
>
> - this would make it safer to expose /proc/kallsyms to user-space
>   profiling, while keeping the random offset a kernel-internal secret.
>
> - RIP information in profiling streams would thus not contain the
>   kernel random offset either.
>
>The other approach would be what your series does, to keep all the raw,
>
>randomized output and to assume that users who are allowed to access to
>
>logs or profiling can learn the random offset.
>
>I tend to lean towards the 'raw' approach that you picked, but an
>argument 
>can be made for both approaches - and in any case I haven't seen this 
>discussed to conclusion with cons/pros listed and a consensus/decision 
>reached.
>
>Thanks,
>
>	Ingo

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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