Re: [PATCH] x86: Lock down MSR writing in secure boot

From: H. Peter Anvin
Date: Fri Feb 08 2013 - 20:22:55 EST

On 02/08/2013 03:26 PM, Matthew Garrett wrote:
> On Sat, 2013-02-09 at 00:06 +0100, Borislav Petkov wrote:
>> On Fri, Feb 08, 2013 at 02:30:52PM -0800, H. Peter Anvin wrote:
>>> Also, keep in mind that there is a very simple way to deny MSR access
>>> completely, which is to not include the driver in your kernel (and not
>>> allow module loading, but if you can load modules you can just load a
>>> module to muck with whatever MSR you want.)
>> I was contemplating that too. What is the use case of having
>> msr.ko in a secure boot environment? Isn't that an all-no-tools,
>> you-can't-do-sh*t-except-what-you're-explicitly-allowed-to environment which
>> simply doesn't need to write MSRs in the first place?
> Well, sure, distributions could build every kernel twice. That seems a
> little excessive, though.

You don't have to build the kernel twice to exclude a loadable module.


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