linux-kernel - Re: [PATCH v13 3/3] trace,x86: Add irq vector tracepoints

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Date:	Tue, 04 Jun 2013 11:15:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Seiji Aguchi <seiji.aguchi@....com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, mingo@...e.hu, bp@...en8.de,
	linux-edac@...r.kernel.org, tony.luck@...el.com,
	dle-develop@...ts.sourceforge.net, tomoki.sekiyama@....com
Subject: Re: [PATCH v13 3/3] trace,x86: Add irq vector tracepoints

On 06/03/2013 04:53 PM, Steven Rostedt wrote:
> 
> This way we wont be opening up any easy root holes where if a process
> finds a way to modify some arbitrary kernel memory, we can prevent it
> from modifying the current_idt_descr_ptr and have a nice way to exploit
> the IDT. Sure, one can argue that if they can modify arbitrary kernel
> memory, we may already be lost, but lets not make it easier for them
> than need be.
> 

I don't like current_idt_descr_ptr if we can avoid it.  It is a direct
proxy for reading and writing the original IDT, in other words, it
really hasn't really addressed the issue.

What I'm thinking we really should have is a function that returns the
IDT that we currently should be using, based on the current state.  If
that state is, say, tracing on/off and NMI on/off, then that can be
indicated by bits in a state vector.

The point is that the IDT address itself should not be mutable state if
it can be at all avoided.

	-hpa

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