linux-kernel - Re: [PATCH V3 08/11] kexec: Disable at runtime if the kernel enforces module loading restrictions

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Date:	Sun, 8 Sep 2013 16:59:40 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH V3 08/11] kexec: Disable at runtime if the kernel
 enforces module loading restrictions

On Sun, 2013-09-08 at 09:39 -0700, Greg KH wrote:

> But I want, for other reasons (i.e. safety in layers), signed kernel
> modules.  I also might actually want some debugfs files in some random
> driver (like this series removes).

You want a configuration that makes no sense. There's no reason that the
kernel should make that easy.

> Heck, look at Red Hat.  They have been shipping signed kernel modules
> for _years_ and yet they do not disable kexec.  Have they been "doing it
> wrong" all of this time?   Perhaps people want signed modules just for
> support reasons, not "security" reasons.

Then they do what Red Hat does and don't set CONFIG_SIG_ENFORCE.

> Don't take away those options.

Where's the option to let me let unprivileged users set random MSRs?
Where's the option to let root disable STRICT_DEVMEM at runtime? We
don't offer these options because *they make no sense*. Locking your
door while leaving your window open may make you feel better, but it
doesn't improve the security of your house.

-- 
Matthew Garrett <matthew.garrett@...ula.com>