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

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Message-ID: <516348F6.1080902@zytor.com>
Date:	Mon, 08 Apr 2013 15:47:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kees Cook <keescook@...omium.org>
CC:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>, 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,
	virtualization@...ts.linux-foundation.org,
	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 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?

	-hpa


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