linux-kernel - Re: mmotm 2014-07-02-15-07 uploaded (stack protector)

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Message-Id: <20140702175635.79d54c44.akpm@linux-foundation.org>
Date:	Wed, 2 Jul 2014 17:56:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kees Cook <kees@...flux.net>
Cc:	Andi Kleen <ak@...ux.intel.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	linux-kernel@...r.kernel.org, linux-next@...r.kernel.org,
	sfr@...b.auug.org.au, mhocko@...e.cz
Subject: Re: mmotm 2014-07-02-15-07 uploaded (stack protector)

On Wed, 2 Jul 2014 17:51:00 -0700 Kees Cook <kees@...flux.net> wrote:

> > It's hard to tell what the original author wanted, perhaps they wanted
> > it to error out. It looks intentional. Clearly they didn't think of randconfig
> > though.
> 
> The problem is that if you make kbuild hard-fail when selecting this missing
> compiler option, you can never switch it back because "make menuconfig" will
> refuse to build since the compiler option would be missing. Being silent
> about the missing option (and/or falling back to other options) means that
> you could get two different kernel features selection with the same CONFIG_*
> set, depending on the kernel, which is extremely bad ("I selected
> stack-protector-strong but it built without it?!").
> 
> So, the middle ground was to warn about it during the kbuild logic so
> you could find the source of the problem, but ultimately fail the build
> when the compiler doesn't support it so there weren't any silent failure
> modes.

--- a/Makefile~a
+++ a/Makefile
@@ -630,6 +630,9 @@ KBUILD_CFLAGS += $(call cc-option,-Wfram
 endif
 
 # Handle stack protector mode.
+#
+# This space reserved for Kees
+#
 ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
   stackp-flag := -fstack-protector
   ifeq ($(call cc-option, $(stackp-flag)),)
_

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