linux-kernel - Re: [PATCH v2] kexec: add sysctl to disable kexec

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Message-ID: <20131210191409.GE13909@redhat.com>
Date:	Tue, 10 Dec 2013 14:14:09 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	Rob Landley <rob@...dley.net>,
	Eric Biederman <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	kexec@...ts.infradead.org
Subject: Re: [PATCH v2] kexec: add sysctl to disable kexec

On Tue, Dec 10, 2013 at 10:54:00AM -0800, H. Peter Anvin wrote:
> On 12/10/2013 10:33 AM, Vivek Goyal wrote:
> > On Tue, Dec 10, 2013 at 08:32:38AM -0800, H. Peter Anvin wrote:
> >> Of course it isn't.
> > 
> > I am not sure what are you trying to say. This is too brief.
> > 
> > Thanks
> > Vivek
> > 
> 
> Of course it is not sufficient.  Once you can get arbitrary code into
> kernel space (CPL 0) you can do anything, and "disabling jump back" is
> just a speed bump.

Agreed that disabling jump back is only a speed bump.

Kees, so how would be use this knob?

- If I put it in some init script, then root will permission to modify
  and remove it.

- Can one specify sysctl parameters on command line? If yes, then one
  can disable this using kernel command line and in that case kdump will
  be disabled too.

Thanks
Vivek
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