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Message-ID: <CAGXu5j+fWeinnBr3JLkLt-M4N8uSXzP9MiRF20h37_WABQ1Rrw@mail.gmail.com>
Date: Mon, 8 Apr 2013 16:05:54 -0700
From: Kees Cook <keescook@...omium.org>
To: "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc: Ingo Molnar <mingo@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.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>,
Borislav Petkov <borislav.petkov@....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] x86: make IDT read-only
On Mon, Apr 8, 2013 at 3:56 PM, Maciej W. Rozycki <macro@...ux-mips.org> wrote:
> On Mon, 8 Apr 2013, Kees Cook wrote:
>
>> This makes the IDT unconditionally read-only. This primarily removes
>> the IDT from being a target for arbitrary memory write attacks. It has
>> an added benefit of also not leaking (via the "sidt" instruction) the
>> kernel base offset, if it has been relocated.
> [...]
>> --- a/arch/x86/kernel/cpu/intel.c
>> +++ b/arch/x86/kernel/cpu/intel.c
>> @@ -215,7 +201,6 @@ 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;
>> }
>
> FWIW the change looks reasonable to me, however given that that it makes
> the arrangement unconditional and there is no longer a workaround to
> enable I think it would make sense to remove the conditional block quoted
> above altogether, along with the f00f_workaround_enabled variable itself
> (alternatively "Intel Pentium with F0 0F bug" alone could be printed
> instead and the name of the variable adjusted to make sense with the new
> meaning -- up to you to decide).
Actually, I take it back. The other portion of the workaround is still
active (in mm/fault.c), and this chunk announces it, so I'm going to
leave it as-is.
-Kees
--
Kees Cook
Chrome OS Security
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