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

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Message-ID: <4F4547C6.8050001@zytor.com>
Date:	Wed, 22 Feb 2012 11:53:42 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Will Drewry <wad@...omium.org>
CC:	Indan Zupancic <indan@....nu>, 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,
	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 02/22/2012 11:47 AM, Will Drewry wrote:
>>
>> I highly disagree with every filter having to check the mode: Filters that
>> don't check the arch on e.g. x86 are buggy, so they have to check it, even
>> if it's a 32-bit or 64-bit only system, the filters can't know that and
>> needs to check the arch at every syscall entry. All other info in the data
>> depends on the arch, because of this there isn't much code to share between
>> the two archs, so you can as well have one filter for each arch.
>>
>> 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.
> 
> This was roughly how I first implemented compat and non-compat
> support.  It causes some implicit behavior across inheritance that is
> not nice though.
> 

This is trivially doable at the BPF level, right?  Just make this the
first instruction in the program (either deny or jump to a separate
program branch)... and then there is still "one program" without any
weird inheritance issues?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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