linux-kernel - Re: [RFC PATCH 4/7] kconfig: support new special property shell=

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Date:   Sun, 11 Feb 2018 13:05:12 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Ulf Magnusson <ulfalizer@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        "Luis R . Rodriguez" <mcgrof@...e.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Pavel Machek <pavel@....cz>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH 4/7] kconfig: support new special property shell=

On Sun, Feb 11, 2018 at 10:34 AM, Ulf Magnusson <ulfalizer@...il.com> wrote:
> On Sun, Feb 11, 2018 at 6:56 PM, Kees Cook <keescook@...omium.org> wrote:
>> Old? That's not the case. The check for -fno-stack-protector will
>> likely be needed forever, as some distro compilers enable
>> stack-protector by default. So when someone wants to explicitly build
>> without stack-protector (or if the compiler's stack-protector is
>> detected as broken), we must force it off for the kernel build.
>
> What I meant is whether it makes sense to test if the
> -fno-stack-protector option is supported. Can we reasonably assume
> that passing -fno-stack-protector to the compiler won't cause an
> error?

That isn't something I've tested; but I can check if it's useful.

> Is it possible to build GCC with no "no stack protector" support? Do
> we need to support any compilers that would choke on the
> -fno-stack-protector flag itself?
>
> If we can reasonably assume that passing -fno-stack-protector is safe,
> then CC_HAS_STACKPROTECTOR_NONE isn't needed.

Well, there are two situations:

- does the user want to build _without_ stack protector? (which is
something some people want to do, no matter what I think of it)

- did _AUTO discover that stack protector output is broken?

In both cases, we need to pass -fno-stack-protector in case the distro
compiler was built with stack protector enabled by default.

-Kees

-- 
Kees Cook
Pixel Security