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

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Message-ID: <515F4B60.60302@zytor.com>
Date:	Fri, 05 Apr 2013 15:08:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Julien Tinnes <jln@...gle.com>
CC:	Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.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 04/05/2013 03:06 PM, Julien Tinnes wrote:
> 
> Speaking of IDT, and to capture some off-thread discussion here, we
> should remember that the "SGDT" and "SIDT" instructions aren't
> privileged on x86, so user-land can leak these out without any way for
> the kernel to intercept that.
> 
> Adding their own random offsets to these two tables would be very
> useful. This could be done in a later patchset of course.
> 

Yes, if the GDT or IDT position is at all correlated to the kernel
position this is pointless.

	-hpa


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