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Date:	Wed, 22 Feb 2012 17:07:05 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Lutomirski <luto@....edu>
CC:	Indan Zupancic <indan@....nu>, Will Drewry <wad@...omium.org>,
	Ben Hutchings <bhutchings@...arflare.com>,
	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 v10 05/11] seccomp: add system call filtering using BPF

On 02/22/2012 03:51 PM, Andrew Lutomirski wrote:
> On Wed, Feb 22, 2012 at 3:46 PM, Indan Zupancic <indan@....nu> wrote:
>> On Wed, February 22, 2012 20:47, Will Drewry wrote:
>>> On Wed, Feb 22, 2012 at 8:23 AM, Ben Hutchings
>>>> I would have thought the way to make sure the architecture is always
>>>> checked is to pack it together with the syscall number.
>>
>> I missed that suggestion, putting the syscall number and arch in one
>> data field would indeed make it harder to not check the arch.
> 
> Is there enough room?  On x86-64 at least, rax could conceivably be
> extended to 64 bits some day.  Bit 30 is already spoken for by x32.
> 

No it couldn't, because we mask off the high 32 bits and thus it could
(theoretically) break user space.

	-hpa


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

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