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Date: Tue, 9 Apr 2013 17:29:22 -0700
From: Kees Cook <keescook@...omium.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, "x86@...nel.org" <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" <xen-devel@...ts.xensource.com>,
"virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>,
"kernel-hardening@...ts.openwall.com" <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 Tue, Apr 9, 2013 at 5:14 PM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.
I have no objection to removing it, but with CONFIG_F00F_BUG, the trap
handler does still do some checking, and I figured this message was
there to notify people about it.
-Kees
--
Kees Cook
Chrome OS Security
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