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Date: Mon, 16 Apr 2018 11:29:13 -0700
From: Kees Cook <keescook@...omium.org>
To: Alexander Popov <alex.popov@...ux.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Ingo Molnar <mingo@...nel.org>, Laura Abbott <labbott@...hat.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, PaX Team <pageexec@...email.hu>, 
	Brad Spengler <spender@...ecurity.net>, Andy Lutomirski <luto@...nel.org>, 
	Tycho Andersen <tycho@...ho.ws>, 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>, Florian Weimer <fweimer@...hat.com>, 
	Boris Lukashev <blukashev@...pervictus.com>, X86 ML <x86@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 2/6] x86/entry: Add STACKLEAK erasing the kernel stack
 at the end of syscalls

On Fri, Apr 6, 2018 at 7:22 AM, Alexander Popov <alex.popov@...ux.com> wrote:
> This commit introduces the architecture-specific code filling the used
> part of the kernel stack with a poison value before returning to the
> userspace. Full STACKLEAK feature also contains the gcc plugin which
> comes in a separate commit.

Thanks for sending this again! And thanks for the updated reasoning
for why this remains a valuable addition:

https://lkml.kernel.org/r/1523024546-6150-1-git-send-email-alex.popov@linux.com

I, too, remain convinced this is a good protection to have, even as we
slowly remove VLAs and try to improve the compiler's initialization of
stack variables.

Dave, Ingo, Linus: how does this look? With the assembly rewritten
into C, the entry changes are very small:

>  arch/x86/entry/entry_32.S        |  7 ++++++
>  arch/x86/entry/entry_64.S        |  3 +++
>  arch/x86/entry/entry_64_compat.S |  5 ++++
>  arch/x86/entry/erase.c           | 54 ++++++++++++++++++++++++++++++++++++++++

I'd really like to get people's Ack/Review. :)

Laura, can this C version work for arm64 as well?

Thanks,

-Kees

-- 
Kees Cook
Pixel Security

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