linux-kernel - Unnecessary overhead with stack protector.

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Message-ID: <20091015183540.GA8098@redhat.com>
Date:	Thu, 15 Oct 2009 14:35:41 -0400
From:	Dave Jones <davej@...hat.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	esandeen@...hat.com, cebbert@...hat.com
Subject: Unnecessary overhead with stack protector.

113c5413cf9051cc50b88befdc42e3402bb92115 introduced a change that
made CC_STACKPROTECTOR_ALL not-selectable if someone enables CC_STACKPROTECTOR.

We've noticed in Fedora that this has introduced noticable overhead on
some functions, including those which don't even have any on-stack variables.

According to the gcc manpage, -fstack-protector will protect functions with
as little as 8 bytes of stack usage. So we're introducing a huge amount
of overhead, to close a small amount of vulnerability (the >0 && <8 case).

The overhead as it stands right now means this whole option is unusable for
a distro kernel without reverting the above commit.

	Dave

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