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Date: Thu, 25 Jan 2018 18:13:55 +0300
From: Alexander Popov <>
To: Kees Cook <>
Cc:, PaX Team <>,
 Brad Spengler <>, Ingo Molnar <>,
 Andy Lutomirski <>, Tycho Andersen <>,
 Laura Abbott <>, Mark Rutland <>,
 Ard Biesheuvel <>, Borislav Petkov <>,
 Thomas Gleixner <>, "H . Peter Anvin" <>,
 Peter Zijlstra <>, "Dmitry V . Levin"
 <>, X86 ML <>
Subject: Re: [PATCH RFC v7 0/6] Introduce the STACKLEAK feature and a test for

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 <> 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%)

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,

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