linux-kernel - Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace periods

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Message-ID: <20150222184844.GA4262@thin>
Date:	Sun, 22 Feb 2015 10:48:45 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	paulmck@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
	oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace
 periods

On Sun, Feb 22, 2015 at 10:31:26AM -0800, Arjan van de Ven wrote:
> >>To show the boot time, I'm using the timestamp of the "Write protecting" line,
> >>that's pretty much the last thing we print prior to ring 3 execution.
> >
> >That's a little sad; we ought to be write-protecting kernel read-only
> >data as *early* as possible.
> 
> well... if you are compromised before the first ring 3 instruction...
> .... you have a slightly bigger problem than where in the kernel we write protect things.

Definitely not talking about malicious compromise here; malicious code
could just remove the write protection.  However, write-protecting
kernel read-only data also protects against a class of bugs.

- Josh Triplett
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