linux-kernel - Re: [PATCH v2] x86/mm: warn on W+x mappings

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Message-ID: <20151012125548.GE2579@codeblueprint.co.uk>
Date:	Mon, 12 Oct 2015 13:55:48 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Stephen Smalley <sds@...ho.nsa.gov>, x86@...nel.org,
	linux-kernel@...r.kernel.org, keescook@...omium.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>, linux-efi@...r.kernel.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH v2] x86/mm: warn on W+x mappings

On Mon, 12 Oct, at 02:49:36PM, Ingo Molnar wrote:
> 
> 
> So why not unmap them after bootup? Is there any reason to call into EFI code 
> while the system is up and running?

That's where the runtime services code lives. So if you want things
like EFI variables (used by the distro installer, among other things)
you need to map the runtime regions.

You can of course disable that by using the "noefi" kernel parameter,
which should unmap everything for you once you've finished booting.

-- 
Matt Fleming, Intel Open Source Technology Center
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