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Date: Tue, 6 Mar 2018 13:41:22 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Arnd Bergmann <arnd@...db.de>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, 
	Daniel Micay <danielmicay@...il.com>, Ingo Molnar <mingo@...nel.org>, 
	Kees Cook <keescook@...omium.org>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Alexander Popov <alex.popov@...ux.com>, 
	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>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, 
	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>, 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>, 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()

On Tue, Mar 6, 2018 at 1:36 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> You mean have gcc fill in the variables that it thinks is used
> uninitialized with zeros?

No.

It should do it unconditionally.

Because "gcc thinks is used uninitialized" is simply not good enough.

The warning would remain for the case where you don't enable this
hardening feature, so it wouldn't go away.

The warning also wouldn't be *improved*. The warning is simply a
completely a separate thing, and as your example shows is *entirely*
independent of the "make all locals be initialized to zero".

                  Linus

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