linux-kernel - Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr

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Date:	Mon, 29 Jun 2015 11:58:53 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Prarit Bhargava <prarit@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	Len Brown <len.brown@...el.com>,
	Dasaratharaman Chandramouli 
	<dasaratharaman.chandramouli@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr

On Sun, 28 Jun, at 12:10:49PM, Henrique de Moraes Holschuh wrote:
> On Sun, 28 Jun 2015, Prarit Bhargava wrote:
> > Is it easier to blacklist MSRs we don't want generally exposed, or only expose
> > the ones that we think are safe?  That's sort of a devil's advocate sort of
> > question ;) and I'm wondering what the shorter list is.
> 
> The only way to make MSR access safe is to allow it only by whitelisting.
> The x86 platform restricts all MSR access to ring 0 for a damn good reason.

Blacklisting also breaks horribly if you run old kernels on new
hardware.

We need to "fail-closed" if someone tries to access an MSR the kernel
doesn't know about.

-- 
Matt Fleming, Intel Open Source Technology Center
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