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

From: Peter Zijlstra
Date: Thu Feb 09 2017 - 05:27:37 EST

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.