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Message-ID: <CAGXu5j+hoCKBkaknNFQvHYFNuj-FweCPuL2vngCYpb8rcR-qtw@mail.gmail.com>
Date: Sun, 11 Feb 2018 13:35:58 -0800
From: Kees Cook <keescook@...omium.org>
To: Alexander Popov <alex.popov@...ux.com>
Cc: kernel-hardening@...ts.openwall.com, PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>, Ingo Molnar <mingo@...nel.org>,
Andy Lutomirski <luto@...nel.org>, Tycho Andersen <tycho@...ho.ws>, 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>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Dmitry V . Levin" <ldv@...linux.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH RFC v7 0/6] Introduce the STACKLEAK feature and a test for it
On Thu, Jan 25, 2018 at 7:13 AM, Alexander Popov <alex.popov@...ux.com> wrote:
> On 20.01.2018 13:13, Alexander Popov wrote:
>> On 19.01.2018 00:13, Kees Cook wrote:
>>> On Thu, Jan 18, 2018 at 5:09 AM, Alexander Popov <alex.popov@...ux.com> wrote:
>>>> So I don't think that (1) without (2) is actually a good feature. I would
>>>> propose to refrain from separating the stack erasing and the lowest_stack tracking.
>>>
>>> How about an option to clear the _entire_ stack, then, when the plugin
>>> isn't available? That gives us a range of options and provides an easy
>>> way to compare the performance of the tracking. i.e. can compare off,
>>> full, and smart.
>>
>> Yes, I should try it. I'll return with the results of the performance tests.
>> We'll discuss them; if full stack erasing is not too slow, I'll introduce it in
>> the 8'th version of the patch series.
>
> I've made a brief performance test on x86_64 (similar to the test described in
> the cover letter). I guess there might be workloads with higher performance penalty.
>
> Hardware: Intel Core i7-4770, 16 GB RAM
> Test: hackbench -s 4096 -l 2000 -g 15 -f 25 -P
>
> Average time on v4.14.15: 9.194s
> Average time on v4.14.15-stackleak-with-plugin: 9.490 (+3.22%)
> Average time on v4.14.15-stackleak-full-erasing: 12.149 (+32.14%)
Yeeeowch. Okay, I'm convinced. :)
> Honestly, I think, it is not worth having this full stack erasing as a separate
> feature. Moreover, it brings some #ifdef conditionals to the erase_kstack()
> code, which don't look nice.
>
> May I ask for your opinion?
>
> Best regards,
> Alexander
-Kees
--
Kees Cook
Pixel Security
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