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Date: Tue, 6 Mar 2018 13:29:37 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: 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>,
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"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Thomas Garnier <thgarnie@...gle.com>,
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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>, 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 1:21 PM, Arnd Bergmann <arnd@...db.de> wrote:
>
> Right, there are two separate problems: the missing warnings
> and the actual uninitialized use. Allocating the stack slots would
> address both but only at an enormous cost. Assigning a value
> would still have a cost, as it would prevent certain other optimizations,
> and it wouldn't help find the missing initializations,
> but the cost would obviously be much lower.
What possible optimization would it prevent?
I cannot think of a single interesting optimization that would be
invalidated by a trivial initialization of 0 to a scalar.
Yes, it can obviously generate some extra code for the "pass pointer
to uninitialized scalar around to be initialized", where it can now
make that stack slot be initialized to zero - so it can generate extra
code. But disabling an optimization?
What did you have in mind?
Linus
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