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Date: Sun, 22 Oct 2017 15:11:57 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alexander Popov <alex.popov@...ux.com>
Cc: kernel-hardening@...ts.openwall.com, keescook@...omium.org,
	pageexec@...email.hu, spender@...ecurity.net,
	Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>,
	tycho@...ker.com, Laura Abbott <labbott@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH RFC v5 0/5] Introduce the STACKLEAK feature and a test
 for it

On Sun, Oct 22, 2017 at 03:22:48AM +0300, Alexander Popov wrote:
 
> These numbers were obtained for the 4th version of the patch series.
> 
> Size of vmlinux (x86_64_defconfig):
>  file size:
>   - STACKLEAK disabled: 35014784 bytes
>   - STACKLEAK enabled: 35044952 bytes (+0.086%)
>  .text section size (calculated by size utility):
>   - STACKLEAK disabled: 10752983
>   - STACKLEAK enabled: 11062221 (+2.876%)

Why no runtime costs? This should not be hard to measure.

> Further work
> =============
> 
>  - Rewrite erase_kstack() in C (if Ingo Molnar insists).

Aside from legacy, is there any sane reason that stuff is in ASM? That
is, I too will insist it being in C unless you can provide good
arguments on why it needs be asm. All it does is memzero() right? And I
would think architectures already have fairly optimized implementations
of that around.

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