Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION

From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"Reshetova, Elena" <elena.reshetova@intel.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	"H. Peter Anvin" <h.peter.anvin@intel.com>,
	Will Deacon <will.deacon@arm.com>,
	David Windsor <dwindsor@gmail.com>,
	Hans Liljestrand <ishkamiel@gmail.com>,
	David Howells <dhowells@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>
Subject: Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION
Date: Thu, 9 Feb 2017 11:27:03 +0100	[thread overview]
Message-ID: <20170209102703.GB6500@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGXu5j+vSECyQgF2a5UWe1-FOMNFyZTLkM0o30Z7KOm=-EKuGQ@mail.gmail.com>

On Wed, Feb 08, 2017 at 01:20:26PM -0800, Kees Cook wrote:

> Ooooh, that is intense. And the trampolines (EX_REG_HANDLERs) are all
> just there to catch whatever register gcc decides to stuff the value
> into? *cover face* Sure, okay. :)

Right, they shouldn't be big functions, but barring whole program LTO
there's just no knowing which are unused.

> I wonder how many existing WARN callsites could be repurposed to use this?

At the very least all WARN/BUG instances with trivial @format argument
that are inlined I think. For example, things like:

static inline some_function()
{
	/* ... */
	WARN(cond, "blah blah blah\n");
	/* ... */
}

where the format has no arguments. Here we can out-of-line the printk()
stuff, which, as is the purpose here, shrinks the size of the inline.