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Message-ID: <20180312082226.ciggxv37cgcazs3j@gmail.com>
Date: Mon, 12 Mar 2018 09:22:26 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Arnd Bergmann <arnd@...db.de>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Daniel Micay <danielmicay@...il.com>,
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()
* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Tue, Mar 6, 2018 at 1:41 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > The warning would remain for the case where you don't enable this
> > hardening feature, so it wouldn't go away.
>
> Side note: if in ten years we'd have a minimum gcc version that we
> could just unconditionally say "auto (scalars) initialize to zero",
> then we'd just make that be the *semantics*, and the warning would
> obviously simply not ever be an issue.
Btw., I'd suggest we initialize aggregate types to zero as well, and then work
from there by marking exceptions via attributes.
>From what I've seen over 90% of 'tricky' initialization sequences either don't
matter to performance, or are unnecessarily complicated.
I.e. let's eliminate VLAs and let's also make the object initialization aspect of
the C language reliably and broadly safe by default (via a GCC plugin) with no
exceptions, and allow an opt-in mechanism for more fragile (but faster if coded
correctly) constructs.
Is it possible to implement this "safe automatic variable initialization" language
feature via a GCC plugin robustly, while still keeping code generation sane? (i.e.
no forced allocation of stack slots, etc.) It should be a superset of
CONFIG_GCC_PLUGIN_STRUCTLEAK=y.
Plugin support is present in GCC version 4.5 and higher, correct? So if such a
plugin is possible we could raise the minimum GCC version to support it
unconditionally.
I suspect a fair chunk of all kernel CVEs would go away if we fixed the C language
this way.
Thanks,
Ingo
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