linux-kernel - Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention

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Date:	Fri, 21 Sep 2012 17:41:34 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linda Wang <lwang@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention

"H. Peter Anvin" <hpa@...ux.intel.com> writes:

> On 09/21/2012 03:07 PM, Eric W. Biederman wrote:
>> 
>> Have you tested kexec in this environment?
>> 
>> This is the kind of cpu feature that when we enable it, frequently we
>> have to do something on the kexec path.
>> 
>> At a quick skim it looks like the kexec path is using kernel page table
>> entries and clearing all bits from cr4 except X86_CR4_PAE so I don't
>> actually expect this change will require anything on the kexec path.
>> 
>
> I have not, no, but as you quite correctly point out that shouldn't
> affect things.
>
> We should also change the kernel to start clean with CR4 -- the purpose
> of CR4 is to indicate which CPU features the OS is opting into.
>
> I think we do on x86-64 but not on x86-32 at the moment.
>
> This is an unrelated problem, though, and can be addressed later.

Agreed.  I just was just curious where things stood.

Eric

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