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

From: Matthew Garrett
Date: Wed Feb 13 2013 - 01:42:09 EST

On Tue, 2013-02-12 at 22:33 -0800, H. Peter Anvin wrote:

> 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.

Well right, that's the point of this patchset - it adds some extra
permission checks to some of the existing CAP_SYS_RAWIO checks.
CAP_SYS_RAWIO hasn't meant "I can perform arbitrary pio and mmio" for
years - it means "I can do things that might maybe break something
somehow". So sure, removing CAP_SYS_RAWIO would give us basically all
the security we want in a secure boot environment, but it would also
block things that we *want* to work.
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