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

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Date:	Thu, 7 May 2009 00:13:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Markus Gutschke (顧孟勤) <markus@...gle.com>
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


* Markus Gutschke (顧孟勤) <markus@...gle.com> wrote:

> 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.

doing a (per arch) bitmap of harmless syscalls and replacing the 
mode1_syscalls[] check with that in kernel/seccomp.c would be a 
pretty reasonable extension. (.config controllable perhaps, for 
old-style-seccomp)

It would probably be faster than the current loop over 
mode1_syscalls[] as well.

	Ingo
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