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Message-ID: <CA+55aFwgmTaaA8QqMGm+VzRNbpKxDXbq2MtKyayyq8f+=PqWqA@mail.gmail.com>
Date: Tue, 6 Mar 2018 10:56:58 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Daniel Micay <danielmicay@...il.com>
Cc: 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>,
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()
On Tue, Mar 6, 2018 at 7:16 AM, Daniel Micay <danielmicay@...il.com> wrote:
>
> Zeroing locals isn't very expensive because the compiler has a chance
> to optimize it out when it can figure out it isn't needed and they're
> almost always used.
I thought I saw Kees with some stats, and it wasn't even noticeable.
But maybe I mis-remember.
I definitely like the "zero local variables", and would actually
prefer something even stronger than GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
(although I can't actually read gcc plugins, so I'm just going by
name).
It's not necessarily just struct, it can very much be arrays and
regular automatic variables too.
And yes, we might want to have some override switch for individual
variables ("I really know what I'm doing and I promise I fill it
myself, but the compiler doesn't understand me, look here:").
Linus
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