linux-kernel - Re: [PATCH v8 5/9] seccomp: split mode set routines

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Message-ID: <20140627192753.GA30752@redhat.com>
Date:	Fri, 27 Jun 2014 21:27:53 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	David Drysdale <drysdale@...gle.com>,
	Linux API <linux-api@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-mips@...ux-mips.org,
	linux-arch <linux-arch@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v8 5/9] seccomp: split mode set routines

On 06/27, Kees Cook wrote:
>
> It looks like SMP ARM issues dsb for rmb, which seems a bit expensive.
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204g/CIHJFGFE.htm
>
> ...
>
> I really want to avoid adding anything to the secure_computing()
> execution path. :(

I must have missed something but I do not understand your concerns.

__secure_computing() is not trivial, and we are going to execute the
filters. Do you really think rmb() can add the noticeable difference?

Not to mention that we can only get here if we take the slow syscall
enter path due to TIF_SECCOMP...

Oleg.

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