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

From: H. Peter Anvin
Date: Wed Feb 13 2013 - 01:35:15 EST

On 02/12/2013 10:27 PM, Matthew Garrett wrote:
On Tue, 2013-02-12 at 22:12 -0800, H. Peter Anvin wrote:

Sounds like you are thinking of CAP_SYS_ADMIN, but I don't really see a
huge difference between MSRs and I/O control registers... just different
address spaces.

Not having CAP_SYS_RAWIO blocks various SCSI commands, for instance.
These might result in the ability to write individual blocks or destroy
the device firmware, but do any of them permit modifying the running

That is just batshit crazy. If you have CAP_SYS_RAWIO you can do iopl() which means you can reprogram your northbridge, at which point you most definitely *can* modify the running kernel.

And some SCSI driver requires this??!


H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

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