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 17:38:13 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Kees Cook <keescook@...omium.org>,
	Greg KH <gregkh@...uxfoundation.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 10:32 -0700, James Bottomley wrote:
> On Sun, 2013-09-08 at 17:27 +0000, Matthew Garrett wrote:
> > > It's an argument that CAP_SYS_BOOT is too powerful yes, but if you
> > > recall, I said I keep that one.  In the rather lame analogy, what I do
> > > by giving away CAP_SYS_MODULE and enforcing module signing while keeping
> > > CAP_SYS_BOOT is allow people into my conservatory to play with the
> > > plants but not into my house to steal the silver ... saying CAP_SYS_BOOT
> > > is too powerful doesn't affect that use case because I haven't given
> > > away CAP_SYS_BOOT.
> > 
> > Ok, sorry, I had your meaning inverted. Yes, permitting the loading of
> > signed modules while preventing the use of kexec is a completely
> > reasonable configuration - so reasonable that it's what this patch
> > causes the kernel to do automatically. 
> 
> Well, no, it doesn't because with this patch, *I* can't use kexec ...
> you've just locked me out of my own house.

Hm. Ok, that's a more compelling argument than Greg's. Let me think
about whether there's a convenient way of supporting this.

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