linux-kernel - Re: [PATCH, v2] x86: use the right protections for split-up pagetables

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Message-ID: <20090220080246.GA28669@elte.hu>
Date:	Fri, 20 Feb 2009 09:02:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Huang Ying <ying.huang@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH, v2] x86: use the right protections for split-up
	pagetables


* Ingo Molnar <mingo@...e.hu> wrote:

> [ Huang Ying also experienced problems in this area when writing
>   the EFI code, but the real bug in split_large_page() was not
>   realized back then. ]

> -	 * On Intel the NX bit of all levels must be cleared to make a
> -	 * page executable. See section 4.13.2 of Intel 64 and IA-32
> -	 * Architectures Software Developer's Manual).

Hm, in hindsight, we should have noticed this bug sooner - when 
the NX comment above was added. There's never any good reason to 
play protection games with higher-level pagetable entries. We 
dont do it to user-space pagetables either - we just populate 
them to _PAGE_TABLE and that's it.

	Ingo
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