kernel-hardening - Re: [PATCH 0/3] gcc-plugins: Introduce stackinit plugin

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Date: Tue, 29 Jan 2019 03:12:24 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>,
 Laura Abbott <labbott@...hat.com>, xen-devel@...ts.xenproject.org,
 dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
 linux-usb@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org, dev@...nvswitch.org, linux-kbuild@...r.kernel.org,
 linux-security-module@...r.kernel.org, kernel-hardening@...ts.openwall.com,
 Greg KH <gregkh@...uxfoundation.org>, Jann Horn <jannh@...gle.com>,
 William Kucharski <william.kucharski@...cle.com>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Edwin Zimmerman <edwin@...mainstreet.net>,
 Matthew Wilcox <willy@...radead.org>,
 Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [PATCH 0/3] gcc-plugins: Introduce stackinit plugin

On 23.01.2019 14:03, Kees Cook wrote:
> This adds a new plugin "stackinit" that attempts to perform unconditional
> initialization of all stack variables

Hello Kees! Hello everyone!

I was curious about the performance impact of the initialization of all stack
variables. So I did a very brief test with this plugin on top of 4.20.5.

hackbench on Intel Core i7-4770 showed ~0.7% slowdown.
hackbench on Kirin 620 (ARM Cortex-A53 Octa-core 1.2GHz) showed ~1.3% slowdown.

This test involves the kernel scheduler and allocator. I can't say whether they
use stack aggressively. Maybe performance tests of other subsystems (e.g.
network subsystem) can show different numbers. Did you try?

I've heard a hypothesis that the initialization of all stack variables would
pollute CPU caches, which is critical for some types of computations. Maybe some
micro-benchmarks can disprove/confirm that?

Thanks!
Best regards,
Alexander

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