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Date: Wed, 1 Feb 2017 21:13:55 -0800
From: Andy Lutomirski <luto@...nel.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Garnier <thgarnie@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, 
	Andrey Ryabinin <aryabinin@...tuozzo.com>, Alexander Potapenko <glider@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Kees Cook <keescook@...omium.org>, 
	Andy Lutomirski <luto@...nel.org>, Arjan van de Ven <arjan@...ux.intel.com>, 
	Paul Gortmaker <paul.gortmaker@...driver.com>, Borislav Petkov <bp@...e.de>, 
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	Jiri Kosina <jikos@...nel.org>, Matt Fleming <matt@...eblueprint.co.uk>, 
	Ard Biesheuvel <ard.biesheuvel@...aro.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, 
	Juergen Gross <jgross@...e.com>, Rusty Russell <rusty@...tcorp.com.au>, 
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	Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, 
	X86 ML <x86@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, kasan-dev <kasan-dev@...glegroups.com>, 
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	kvm list <kvm@...r.kernel.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2 3/3] x86: Make the GDT remapping read-only on 64 bit

On Wed, Feb 1, 2017 at 1:15 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Thomas Garnier <thgarnie@...gle.com> wrote:
>
>> This patch makes the GDT remapped pages read-only to prevent corruption.
>> This change is done only on 64 bit.
>


>>
>> -     table_base = gdt->address;
>> +     table_base = (unsigned long)get_current_direct_gdt();
>
> Instead of spreading these type casts far and wide please introduce another
> accessor the returns 'unsigned long':
>
>         get_cpu_gdt_rw_vaddr()
>

That whole function is an abomination.  How about replacing 'unsigned
long table_base' with 'struct desc_struct *table'?  If you're feeling
really adventurous, *delete* that function and replace all of its
users with something sane.

--Andy

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