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

[Andrew Morton]

On Wed, 2 Jul 2014 17:51:00 -0700 Kees Cook <kees@xxxxxxxxxxx> 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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