linux-kernel - Re: [PATCHv3] kcov: reject open when kernel not instrumented

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Date:	Fri, 17 Jun 2016 16:48:16 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Kees Cook <keescook@...omium.org>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morse <james.morse@....com>,
	Michal Marek <mmarek@...e.com>
Subject: Re: [PATCHv3] kcov: reject open when kernel not instrumented

On Fri, Jun 17, 2016 at 08:42:28AM -0700, Kees Cook wrote:
> On Fri, Jun 17, 2016 at 2:39 AM, Mark Rutland <mark.rutland@....com> wrote:
> > If the toolchain does not support -fsanitize-coverage=trace-pc, we blat
> > this option from CFLAGS_KCOV, and build the kernel without
> > instrumentation, even if CONFIG_KCOV was selected. However, we still
> > build the rest of the kcov infrastructure, and expose a kcov file under
> > debugfs. This can be confusing, as the kernel will appear to support
> > kcov, yet will never manage to sample any trace PC values. While we do
> > note this fact at build time, this may be missed, and a user may not
> > have access to build logs.
> 
> Do you want to refuse to build if the compiler doesn't support the
> flag?

I would also be happy with that, so it's up to Alexander and Dmitry.

> I finally figured out how to do this, I think, for
> -fstack-protector:
> 
> http://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/commit/?h=kbuild/stackprotector&id=600c1bd5f8647a8470dc2fc5a8697e3eafb5fd52
> 
> If you wanted, the CONFIG_KCOV test could live under the same
> prepare-compiler-check target.

Alexander, Dmitry, thoughts?

Thanks,
Mark.