linux-kernel - Re: [PATCH v10 05/11] seccomp: add system call filtering using BPF

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Message-ID: <1329920626.3258.174.camel@deadeye>
Date:	Wed, 22 Feb 2012 14:23:46 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Indan Zupancic <indan@....nu>
CC:	Will Drewry <wad@...omium.org>, <linux-kernel@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<kernel-hardening@...ts.openwall.com>, <netdev@...r.kernel.org>,
	<x86@...nel.org>, <arnd@...db.de>, <davem@...emloft.net>,
	<hpa@...or.com>, <mingo@...hat.com>, <oleg@...hat.com>,
	<peterz@...radead.org>, <rdunlap@...otime.net>,
	<mcgrathr@...omium.org>, <tglx@...utronix.de>, <luto@....edu>,
	<eparis@...hat.com>, <serge.hallyn@...onical.com>,
	<djm@...drot.org>, <scarybeasts@...il.com>, <pmoore@...hat.com>,
	<akpm@...ux-foundation.org>, <corbet@....net>,
	<eric.dumazet@...il.com>, <markus@...omium.org>,
	<keescook@...omium.org>
Subject: Re: [PATCH v10 05/11] seccomp: add system call filtering using BPF

On Wed, 2012-02-22 at 09:19 +0100, Indan Zupancic wrote:
[...]
> Alternative approach: Tell the arch at filter install time and only run the
> filters with the same arch as the current system call. If no filters are run,
> deny the systemcall.
>
> Advantages:
> 
> - Filters don't have to check the arch every syscall entry.
> 
> - Secure by default. Filters don't have to do anything arch specific to
>   be secure, no surprises possible.
> 
> - If a new arch comes into existence, there is no chance of old filters
>   becoming buggy and insecure. This is especially true for archs that
>   had only one mode, but added another one later on: Old filters had no
>   need to check the mode at all.
[...]

What about when there are multiple layers of restrictions?  So long as
any one layer covers the new architecture, there is no default-deny even
though the other layers might not cover it.

I would have thought the way to make sure the architecture is always
checked is to pack it together with the syscall number.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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