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

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Message-ID: <20150628151049.GB20989@khazad-dum.debian.net>
Date:	Sun, 28 Jun 2015 12:10:49 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	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 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.

Also, such a whitelist would most likely need to be vendor and model-aware,
and to differentiate "allow reads" from "allow writes"...

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
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