linux-kernel - Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

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Message-ID: <4F3DB9E8.7040406@zytor.com>
Date:	Thu, 16 Feb 2012 18:22:32 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Lutomirski <luto@....edu>
CC:	Indan Zupancic <indan@....nu>, 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, mingo@...hat.com, oleg@...hat.com,
	peterz@...radead.org, rdunlap@...otime.net, mcgrathr@...omium.org,
	tglx@...utronix.de, 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 v8 3/8] seccomp: add system call filtering using BPF

On 02/16/2012 06:16 PM, Andrew Lutomirski wrote:
> 
> Is there really no syscall that cares about endianness?
> 
> Even if it ends up working, forcing syscall arguments to have a
> particular endianness seems like a bad decision, especially if anyone
> ever wants to make a 64-bit BPF implementation.  (Or if any
> architecture adds 128-bit syscall arguments to a future syscall
> namespace or whatever it's called.  x86-64 has 128-bit xmm
> registers...)
> 

Not to mention that the reshuffling code will add totally unnecessary
cost to the normal operation.  Either way, Indan has it backwards ... it
*is* one field, the fact that two operations is needed to access it is a
function of the underlying byte code, and even if the byte code can't
support it, a JIT could merge adjacent operations if 64-bit operations
are possible -- or we could (and arguably should) add 64-bit opcodes in
the future for efficiency.

	-hpa

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

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