linux-kernel - Re: [PATCH v2 3/4] x86, boot: Implement ASLR for kernel memory sections (x86

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Date:	Mon, 2 May 2016 15:00:51 -0700
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Thomas Garnier <thgarnie@...gle.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Kees Cook <keescook@...omium.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Jonathan Corbet <corbet@....net>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Toshi Kani <toshi.kani@....com>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Alexander Popov <alpopov@...ecurity.com>,
	Joerg Roedel <jroedel@...e.de>, Dave Young <dyoung@...hat.com>,
	Baoquan He <bhe@...hat.com>, Mark Salter <msalter@...hat.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, gthelen@...gle.com,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 3/4] x86, boot: Implement ASLR for kernel memory
 sections (x86_64)

On 05/02/2016 02:41 PM, Thomas Garnier wrote:
> -#define __PAGE_OFFSET           _AC(0xffff880000000000, UL)
> +#define __PAGE_OFFSET_BASE      _AC(0xffff880000000000, UL)
> +#ifdef CONFIG_RANDOMIZE_MEMORY
> +#define __PAGE_OFFSET           page_offset_base
> +#else
> +#define __PAGE_OFFSET           __PAGE_OFFSET_BASE
> +#endif /* CONFIG_RANDOMIZE_MEMORY */

Do you have any data about the performance impact of this change?  It's
not necessary to have it to merge something like this, I'm just curious
how bad it is.