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

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Date:	Tue, 3 May 2016 12:16:39 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	"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>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
	Greg Thelen <gthelen@...gle.com>,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 3/4] x86, boot: Implement ASLR for kernel memory
 sections (x86_64)

I don't see much difference. I will update the commits on next
iteration with the following:

Kernbench shows almost no difference (-+ less than 1%):

Before:

Average Optimal load -j 12 Run (std deviation):
Elapsed Time 102.63 (1.2695)
User Time 1034.89 (1.18115)
System Time 87.056 (0.456416)
Percent CPU 1092.9 (13.892)
Context Switches 199805 (3455.33)
Sleeps 97907.8 (900.636)

After:

Average Optimal load -j 12 Run (std deviation):
Elapsed Time 102.489 (1.10636)
User Time 1034.86 (1.36053)
System Time 87.764 (0.49345)
Percent CPU 1095 (12.7715)
Context Switches 199036 (4298.1)
Sleeps 97681.6 (1031.11)

Hackbench shows 0% difference on average (hackbench 90 repeated 10 times)

attemp,before,after
1,0.076,0.069
2,0.072,0.069
3,0.066,0.066
4,0.066,0.068
5,0.066,0.067
6,0.066,0.069
7,0.067,0.066
8,0.063,0.067
9,0.067,0.065
10,0.068,0.071
average,0.0677,0.0677

Thanks,
Thomas

On Mon, May 2, 2016 at 3:00 PM, Dave Hansen <dave.hansen@...ux.intel.com> wrote:
> 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.