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Date: Mon, 5 Mar 2018 21:25:35 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Laura Abbott <labbott@...hat.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Popov <alex.popov@...ux.com>,
	kernel-hardening@...ts.openwall.com,
	Kees Cook <keescook@...omium.org>, 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>,
	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>,
	"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@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v9 2/7] x86/entry: Add STACKLEAK erasing the kernel
 stack at the end of syscalls

On Mon, Mar 05, 2018 at 11:43:19AM -0800, Laura Abbott wrote:
> On 03/05/2018 08:41 AM, Dave Hansen wrote:
> > On 03/03/2018 12:00 PM, Alexander Popov wrote:
> > >   Documentation/x86/x86_64/mm.txt  |   2 +
> > >   arch/Kconfig                     |  27 ++++++++++
> > >   arch/x86/Kconfig                 |   1 +
> > >   arch/x86/entry/entry_32.S        |  88 +++++++++++++++++++++++++++++++
> > >   arch/x86/entry/entry_64.S        | 108 +++++++++++++++++++++++++++++++++++++++
> > >   arch/x86/entry/entry_64_compat.S |  11 ++++
> > 
> > This is a *lot* of assembly.  I wonder if you tried at all to get more
> > of this into C or whether you just inherited the assembly from the
> > original code?
> > 
> 
> This came up previously http://www.openwall.com/lists/kernel-hardening/2017/10/23/5
> there were concerns about trusting C to do the right thing as well as
> speed.

And therefore the answer to this obvious question should've been part of
the Changelog :-)

Dave is last in a long line of people asking this same question.

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