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

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Message-ID: <505CE638.1030405@linux.intel.com>
Date:	Fri, 21 Sep 2012 15:12:08 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

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.

	-hpa
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