linux-kernel - Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

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Message-ID: <4D56B0E6.5040600@free.fr>
Date:	Sat, 12 Feb 2011 17:10:14 +0100
From:	matthieu castet <castet.matthieu@...e.fr>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Matthias Hopf <mhopf@...e.de>, rjw@...k.pl,
	Andrew Morton <akpm@...ux-foundation.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

H. Peter Anvin a écrit :
> On 02/07/2011 11:59 AM, castet.matthieu@...e.fr wrote:
>> For .39 I hope we could remove most of the RWX rights after init (This means
>> make low memory trampoline NX or !RW).
>> This should be possible on :
>> - 32 bit if wakeup use trampoline_32 [1] that doesn't enable paging in low
>> memory (can be NX)
>> - trampoline_64 need fix to support NX on data section. It tries to read data
>> section before enabling NX. A possible fix is to use its own page table [2]. And
>> the kernel one can be NX.
> 
> No, you're really barking down the wrong path on this.  The trampoline
> code is tiny; I don't think it is really worth trying to NX-ify it.  The
Even if the trampoline is tiny, a hole is a hole.

The trampoline code job is to jump from low memory (realmode) to somewhere in kernel text.
Why should we enable paging or use kernel page table for doing that ?

> additional complexity caused by not being able to execute in this space
> will really damage some other incoming code, so it isn't an option as
> far as I'm concerned.
> 
What do you plan to add that won't be compatible with that ?


Matthieu

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