Re: [PATCH v2] kexec: add sysctl to disable kexec

From: Vivek Goyal <vgoyal@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Matthew Garrett <matthew.garrett@nebula.com>,
	Rik van Riel <riel@redhat.com>, Kees Cook <keescook@chromium.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	kexec@lists.infradead.org, LKML <linux-kernel@vger.kernel.org>,
	Eric Biederman <ebiederm@xmission.com>,
	Rob Landley <rob@landley.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>, Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v2] kexec: add sysctl to disable kexec
Date: Tue, 10 Dec 2013 13:33:53 -0500	[thread overview]
Message-ID: <20131210183352.GD13909@redhat.com> (raw)
In-Reply-To: <f4fbae55-7d7b-400d-b50f-258002371368@email.android.com>

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

> 
> Vivek Goyal <vgoyal@redhat.com> wrote:
> >On Mon, Dec 09, 2013 at 05:06:10PM -0800, Kees Cook wrote:
> >> On Mon, Dec 9, 2013 at 4:34 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> >> > On 12/09/2013 04:16 PM, Kees Cook wrote:
> >> >> For general-purpose (i.e. distro) kernel builds it makes sense to
> >build with
> >> >> CONFIG_KEXEC to allow end users to choose what kind of things they
> >want to do
> >> >> with kexec. However, in the face of trying to lock down a system
> >with such
> >> >> a kernel, there needs to be a way to disable kexec (much like
> >module loading
> >> >> can be disabled). Without this, it is too easy for the root user
> >to modify
> >> >> kernel memory even when CONFIG_STRICT_DEVMEM and modules_disabled
> >are set.
> >> >>
> >> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >> >> Acked-by: Rik van Riel <riel@redhat.com>
> >> >
> >> > So the logic is to load a crashkernel and then lock down the
> >machine
> >> > before services, networking etc. are enabled?
> >> 
> >> Right, or to just turn it off at boot time if kexec will not be used
> >at all.
> >
> >kdump kernel is loaded with the help of kdump service. Different
> >distro's
> >might have different dependencies for that serivce. But recently in
> >fedora
> >we wait network to come up before starting that service. (So that nfs
> >targets can be mounted and checked for valid dump destinations).
> >
> >IOW, crash kernel is loaded quite late in the game (quite a few
> >services
> >have run and possibly networking is up too). To me, practically one
> >will
> >disable kdump also if you change state of this knob early.
> >
> >Thanks
> >Vivek
> 
> -- 
> Sent from my mobile phone.  Please pardon brevity and lack of formatting.

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