From: Kees Cook <kees@outflux•net>
To: Andi Kleen <ak@linux•intel.com>
Cc: Randy Dunlap <rdunlap@infradead•org>,
akpm@linux-foundation•org, linux-kernel@vger•kernel.org,
linux-next@vger•kernel.org, sfr@canb•auug.org.au, mhocko@suse•cz
Subject: Re: mmotm 2014-07-02-15-07 uploaded (stack protector)
Date: Wed, 2 Jul 2014 18:13:05 -0700 [thread overview]
Message-ID: <20140703011305.GK5412@outflux.net> (raw)
In-Reply-To: <20140703010019.GS19781@tassilo.jf.intel.com>
On Wed, Jul 02, 2014 at 06:00:19PM -0700, Andi Kleen wrote:
> > 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?!").
>
> The assumption that every flag in a .config has been consciouscly
> selected by a human is a quite dubious one ...
Sure; it was actually via automated config updates that I uncovered this
limitation of kbuild in the first place.
> LTO just turns itself off if the toolchain doesn't support it.
For this situation, it is more surprising to have this option fall back,
since it is a security feature selection. The build must fail in some way if
compiler doesn't match CONFIG.
> > 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.
>
> Longer term it would be of course best to move all the cc-options
> probing into Kconfig. I bet that would speed up builds too.
Absolutely. I presently lack the deep knowledge to figure this out. :)
-Kees
--
Kees Cook @outflux.net
next prev parent reply other threads:[~2014-07-03 1:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-02 22:08 mmotm 2014-07-02-15-07 uploaded akpm
2014-07-02 23:21 ` mmotm 2014-07-02-15-07 uploaded (stack protector) Randy Dunlap
2014-07-03 0:22 ` Andi Kleen
2014-07-03 0:37 ` Randy Dunlap
2014-07-03 0:51 ` Kees Cook
2014-07-03 0:56 ` Andrew Morton
2014-07-03 1:10 ` [PATCH] kbuild: explain stack-protector-strong CONFIG logic Kees Cook
2014-07-03 1:00 ` mmotm 2014-07-02-15-07 uploaded (stack protector) Andi Kleen
2014-07-03 1:13 ` Kees Cook [this message]
2014-07-03 0:57 ` Kees Cook
2014-07-03 1:42 ` Randy Dunlap
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