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

From: H. Peter Anvin
Date: Wed Feb 13 2013 - 01:13:47 EST

On 02/12/2013 09:39 PM, Matthew Garrett wrote:
On Tue, 2013-02-12 at 16:48 -0800, H. Peter Anvin wrote:

OK... what none of this gets into:

Why should CAP_RAWIO be allowed on a secure boot system, when there are
2^n known ways of compromise a system with CAP_RAWIO?

CAP_SYS_RAWIO seems to have ended up being a catchall of "Maybe someone
who isn't entirely root should be able to do this", and not everything
it covers is equivalent to being able to compromise the running kernel.
I wouldn't argue with the idea that maybe we should just reappraise most
of the current uses of CAP_SYS_RAWIO, but removing capability checks
from places that currently have them seems like an invitation for
userspace breakage.

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.


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

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