linux-kernel - Re: [PATCH v2] x86: use fixed read-only IDT

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Date:	Tue, 09 Apr 2013 17:14:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kees Cook <keescook@...omium.org>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Alex Shi <alex.shi@...el.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	xen-devel@...ts.xensource.com,
	virtualization@...ts.linux-foundation.org,
	kernel-hardening@...ts.openwall.com,
	Dan Rosenberg <drosenberg@...curity.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>,
	Eric Northup <digitaleric@...gle.com>
Subject: Re: [PATCH v2] x86: use fixed read-only IDT

On 04/09/2013 09:39 AM, Kees Cook wrote:
> -
>  static void __cpuinit intel_smp_check(struct cpuinfo_x86 *c)
>  {
>  	/* calling is from identify_secondary_cpu() ? */
> @@ -206,8 +192,7 @@ static void __cpuinit intel_workarounds(struct cpuinfo_x86 *c)
>  	/*
>  	 * All current models of Pentium and Pentium with MMX technology CPUs
>  	 * have the F0 0F bug, which lets nonprivileged users lock up the
> -	 * system.
> -	 * Note that the workaround only should be initialized once...
> +	 * system. Announce that the fault handler will be checking for it.
>  	 */
>  	c->f00f_bug = 0;
>  	if (!paravirt_enabled() && c->x86 == 5) {
> @@ -215,7 +200,6 @@ static void __cpuinit intel_workarounds(struct cpuinfo_x86 *c)
>  
>  		c->f00f_bug = 1;
>  		if (!f00f_workaround_enabled) {
> -			trap_init_f00f_bug();
>  			printk(KERN_NOTICE "Intel Pentium with F0 0F bug - workaround enabled.\n");
>  			f00f_workaround_enabled = 1;
>  		}

Why do we care about this message anymore?  It provides no relevant user
information, the flag itself is already in /proc/cpuinfo, and the
message is likely to be wrong since all it does is look for an Intel CPU
with family == 5.

	-hpa


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