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

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Date:	Fri, 26 Jun 2015 17:26:32 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	Brian Gerst <brgerst@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Len Brown <len.brown@...el.com>,
	Dasaratharaman Chandramouli 
	<dasaratharaman.chandramouli@...el.com>
Subject: Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr



On 06/26/2015 03:23 PM, Brian Gerst wrote:
> On Fri, Jun 26, 2015 at 1:52 PM, Prarit Bhargava <prarit@...hat.com> wrote:
>> Customers write system monitoring software for single systems as well as
>> clusters.  In load-balancing software it is useful to know how "busy" a
>> core is.  Unfortunately the only way to get this data is to run as root,
>> or use setcap to allow userspace access for particular programs.  Both of
>> these options are clunky at best.
>>
>> This patch allows read access to the msr dev files which should be okay.
>> No damage can be done by reading the MSR values and it allows non-root
>> users to run system monitoring software.
>>
>> The turbostat code specifically checks for CAP_SYS_RAWIO, which it
>> shouldn't have to and I've removed that code.  Additionally I've modified
>> the turbostat man page to remove documentation about configuring
>> CAP_SYS_RAW_IO.
>>
>> Note: Write access to msr is still restricted with this patch.
> 
> Allowing unrestricted read access to all MSRs is wrong.  Some MSRs
> contain addresses of kernel data structures, which can be used in
> security exploits.
> 
> The proper way to do this is to write a driver to only expose the MSRs
> that the user tools need, and nothing else.

Will do -- At least I got everyone's attention with this :).

P.

> 
> --
> Brian Gerst
> 
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