linux-kernel - Re: [PATCH 2/2] x86-64: seccomp: fix 32/64 syscall hole

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Date:	Wed, 6 May 2009 15:08:40 -0700
From:	Markus Gutschke (顧孟勤) 
	<markus@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	linux-mips@...ux-mips.org, sparclinux@...r.kernel.org,
	linuxppc-dev@...abs.org
Subject: Re: [PATCH 2/2] x86-64: seccomp: fix 32/64 syscall hole

On Wed, May 6, 2009 at 14:54, Ingo Molnar <mingo@...e.hu> wrote:
> Which other system calls would you like to use? Futexes might be
> one, for fast synchronization primitives?

There are a large number of system calls that "normal" C/C++ code uses
quite frequently, and that are not security sensitive. A typical
example would be gettimeofday(). But there are other system calls,
where the sandbox would not really need to inspect arguments as the
call does not expose any exploitable interface.

It is currently awkward that in order to use seccomp we have to
intercept all system calls and provide alternative implementations for
them; whereas we really only care about a comparatively small number
of security critical operations that we need to restrict.

Also, any redirected system call ends up incurring at least two
context switches, which is needlessly expensive for the large number
of trivial system calls. We are quite happy that read() and write(),
which are quite important to us, do not incur this penalty.

Markus
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