linux-kernel - Re: [kernel-hardening] Re: [PATCH] x86: make IDT read-only

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Date:	Wed, 10 Apr 2013 11:41:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Alex Shi <alex.shi@...el.com>,
	Borislav Petkov <borislav.petkov@....com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	Dan Rosenberg <drosenberg@...curity.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>,
	Eric Northup <digitaleric@...gle.com>
Subject: Re: [kernel-hardening] Re: [PATCH] x86: make IDT read-only


* Kees Cook <keescook@...omium.org> wrote:

> > That's the area in which we just map 1:1 to memory.  Anything allocated with 
> > e.g. kmalloc() ends up with those addresses.
> 
> Ah-ha! Yes, I see now when comparing the debug/kernel_page_tables reports. It's 
> just the High Kernel Mapping that we care about. Addresses outside that range 
> are less of a leak. Excellent, then GDT may not be a problem. Whew.

It's still an infoleak to worry about: any function pointers nearby matter, and 
the x86 GDT is obviously full of useful and highly privilege-relevant function 
pointers ...

I have no objections against read-only mapping the GDT as well.

Thanks,

	Ingo
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