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Date: Fri, 5 Apr 2013 16:18:49 -0700
From: Kees Cook <keescook@...omium.org>
To: Borislav Petkov <bp@...en8.de>, Julien Tinnes <jln@...gle.com>, 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>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR

On Fri, Apr 5, 2013 at 1:43 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Fri, Apr 05, 2013 at 01:19:39PM -0700, Julien Tinnes wrote:
>> I think it'd be perfectly ok for OOPS to print out the kernel base.
>
> Yeah, ok, this still would need some massaging of the oops output per
> script, but it shouldn't be a big problem.
>
> Also, you probably need to make clear in the oops itself that the
> addresses have been randomized. Or, is the mere presence of kernel base
> going to imply that?

There is already a hook in the patch that prints the offset:

+dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
+{
+       pr_emerg("Kernel Offset: 0x%lx\n",
+                (unsigned long)&_text - __START_KERNEL);
...
+       atomic_notifier_chain_register(&panic_notifier_list,
+                                       &kernel_offset_notifier);

But of course, this can get improved.

-Kees

--
Kees Cook
Chrome OS Security

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