linux-kernel - Re: [PATCH 3/3] x86: kernel base offset ASLR

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Message-ID: <CAKyRK=iEXpq9KnG_VJMYW-tpBxU_2TGaO_hZRkNY=J+7SNoQkA@mail.gmail.com>
Date:	Fri, 5 Apr 2013 13:19:39 -0700
From:	Julien Tinnes <jln@...gle.com>
To:	Borislav Petkov <bp@...en8.de>, Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <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>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR

On Fri, Apr 5, 2013 at 7:49 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Thu, Apr 04, 2013 at 01:07:35PM -0700, Kees Cook wrote:
>> This creates CONFIG_RANDOMIZE_BASE, so that the base offset of the kernel
>> can be randomized at boot.
>
> Right,
>
> if I'm reading this whole deal correctly, I have an issue with this
> in the sense that if this thing is enabled by default and people are
> running stripped kernels, an oops which is being reported is worth sh*t
> since all the addresses there are random and one simply can't map them
> back to which functions the callstack frames are pointing to. Which will
> majorly hinder debuggability, IMHO...

I think it'd be perfectly ok for OOPS to print out the kernel base.

Restricting access to these oopses becomes a different problem
(privilege separation). Some existing sandboxes (Chromium, vsftpd,
openssh..) are already defending against it.

Julien
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