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Date: Tue, 6 Mar 2018 00:02:49 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
Kernel Hardening <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>,
Richard Sandiford <richard.sandiford@....com>,
Thomas Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Dmitry V . Levin"
<ldv@...linux.org>, Emese Revfy <re.emese@...il.com>,
Jonathan Corbet <corbet@....net>, Andrey Ryabinin <aryabinin@...tuozzo.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Thomas Garnier <thgarnie@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexei Starovoitov <ast@...nel.org>, Josef Bacik <jbacik@...com>,
Masami Hiramatsu <mhiramat@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
Al Viro <viro@...iv.linux.org.uk>, "David S . Miller" <davem@...emloft.net>,
Ding Tianhong <dingtianhong@...wei.com>, David Woodhouse
<dwmw@...zon.co.uk>, Josh Poimboeuf <jpoimboe@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Dominik Brodowski <linux@...inikbrodowski.net>,
Juergen Gross <jgross@...e.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Mathias Krause <minipli@...glemail.com>,
Vikas Shivappa <vikas.shivappa@...ux.intel.com>, Kyle Huey
<me@...ehuey.com>, Dmitry Safonov <dsafonov@...tuozzo.com>,
Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>,
X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v9 4/7] x86/entry: Erase kernel stack in
syscall_trace_enter()
Hello Linus,
Thanks for your reply (despite some strong words).
On 05.03.2018 23:15, Linus Torvalds wrote:
> This is the first I see of any of this, it was apparently not actually
> posted to lkml or anything like that.
I described that below.
> Honestly, what I see just makes me go "this is security-masturbation".
Let me quote the cover letter of this patch series.
STACKLEAK (initially developed by PaX Team):
- reduces the information that can be revealed through kernel stack leak bugs;
- blocks some uninitialized stack variable attacks (e.g. CVE-2017-17712,
CVE-2010-2963);
- introduces some runtime checks for kernel stack overflow detection. It blocks
the Stack Clash attack against the kernel.
So it seems to be a useful feature.
> It doesn't actually seem to help *find* bugs at all. As such, it's
> another "paper over and forget" thing that just adds fairly high
> overhead when it's enabled.
The cover letter also contains the information about the performance impact.
It's 0.6% on the compiling the kernel (with Ubuntu config) and approx 4% on a
very intensive hackbench test.
> I'm NAK'ing it sight-unseen (see above) just because I'm tired of
> these kinds of pointless things that don't actually strive to improve
> on the kernel, just add more and more overhead for nebulous "things
> may happen", and that just make the code uglier.
>
> Why wasn't it even posted to lkml?
That's my mistake. I started to learn that feature 9 month ago, just before
Qualys published the Stack Clash attack (which is blocked by STACKLEAK). I sent
first WIP versions to a short list of people (and had a lot of feedback to work
with). But later unfortunately I didn't adjust the list of recipients.
That was not done intentionally.
> And why isn't the focus of security people on tools to _analyse_ and
> find problems?
You know, I like KASAN and kernel fuzzing as well:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=82f2341c94d270421f383641b7cd670e474db56b
Best regards,
Alexander
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