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

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Message-ID: <CAGXu5j+zz1PyqRM4_Mz_UokD3Y6i6Vj7v_G8W-Ggd1XO_i0MsA@mail.gmail.com>
Date:	Mon, 8 Apr 2013 15:55:10 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"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>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Dan Rosenberg <drosenberg@...curity.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>,
	Eric Northup <digitaleric@...gle.com>
Subject: Re: [PATCH] x86: make IDT read-only

On Mon, Apr 8, 2013 at 3:47 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 04/08/2013 03:43 PM, Kees Cook wrote:
>> This makes the IDT unconditionally read-only. This primarily removes
>> the IDT from being a target for arbitrary memory write attacks. It has
>> an added benefit of also not leaking (via the "sidt" instruction) the
>> kernel base offset, if it has been relocated.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> Cc: Eric Northup <digitaleric@...gle.com>
>
> This isn't quite what this patch does, though, right?  There is still a
> writable IDT mapping at all times, which is different from a true
> readonly IDT, no?

Ah, I guess that's true. I suppose I should say it makes the memory
seen at the "sidt" location read-only. Can we make them both
read-only?

-Kees

--
Kees Cook
Chrome OS Security
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