linux-kernel - Re: Unnecessary overhead with stack protector.

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Message-ID: <20091015190720.GA19467@elte.hu>
Date:	Thu, 15 Oct 2009 21:07:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, esandeen@...hat.com,
	cebbert@...hat.com, Arjan van de Ven <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Unnecessary overhead with stack protector.


(Cc:-ed Arjan too.)

* Dave Jones <davej@...hat.com> wrote:

> 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.

Exactly what workload showed overhead, and how much?

	Ingo
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