linux-kernel - Re: [PATCH 21/30] stack-protector: test compiler capability in Kconfig and drop AUTO mode

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Message-ID: <CAGXu5jLt4xoxXTw83-npD4WmumPzSC9WnbOkkDoR=VYa5R4rYw@mail.gmail.com>
Date:   Fri, 13 Apr 2018 09:41:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild <linux-kbuild@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Emese Revfy <re.emese@...il.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 21/30] stack-protector: test compiler capability in
 Kconfig and drop AUTO mode

On Thu, Apr 12, 2018 at 10:06 PM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> +stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
> +stackp-flags-$(CONFIG_CC_STACKPROTECTOR)          := -fstack-protector
> +stackp-flags-$(CONFIG_CC_STACKPROTECTOR_STRONG)   := -fstack-protector-strong
> +
> +KBUILD_CFLAGS += $(stackp-flags-y)

So, technically, this works just fine. I wonder if it has an overly
confusing result, in that the compiler under normal situations will
see:

gcc ... -fno-stack-protector -fstack-protector -fstack-protector-strong ...

How about something like this instead:

ifdef CONFIG_CC_STACKPROTECTOR_STRONG
KBUILD_CFLAGS += -fstack-protector-strong
else
ifdef CONFIG_CC_STACKPROTECTOR
KBUILD_CFLAGS += -fstack-protector
else
KBUILD_CFLAGS += -fno-stack-protector
endif
endif

-Kees

-- 
Kees Cook
Pixel Security