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

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Message-ID: <20151012141754.GA6621@gmail.com>
Date:	Mon, 12 Oct 2015 16:17:54 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
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


* Matt Fleming <matt@...eblueprint.co.uk> wrote:

> 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.

So EFI variables could be queried during bootup and saved on the Linux side.

Calling into firmware after the kernel has booted up is fragile in general - 
beyond W+X the security considerations.

Thanks,

	Ingo
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