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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